1. Engineering Standards Update201 P Avenue East, P.O. Box 1997, Kalispell, MT 59903 Phone (406) 758-7720 — Fax (406) 758-7831
www.kalispell.com
REPORT TO: Mayor and City Council
FROM: James C. Hansz, P.E., Director of Public Works
SUBJECT: Update of Engineering Standards
MEETING DATE: Work Session, September 28, 2009
Periodically, the City updates its Standards for Design and Construction to ensure the standards
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and methods used in construction, and to ensure the standards reflect the best practices necessary to
support a vibrant and growing community. Several changes have occurred since the last update, most
notably the City is now regulated by permit from MDEQ for the discharge of municipal storm water
under the State permitting program commonly referred to as MS4. This new permit has many elements
and we have worked several years toward their full implementation. One critical element has been the
development and implementation of very specific standards for storm water related construction. The
inclusion of these storm water standards into the City's engineering standards comprises the bulk of
changes within the document. Several other smaller changes have also been incorporated. As done in the
past, all these proposed changes have been circulated throughout the local engineering community and
their comments have been addressed and where appropriate incorporated into the present document.
Susie Turner and Paul Burnham will provide an overview of the changes and will answer your
questions. Once City Council's questions have been answered, the next step is bring the standards
forward for adopting by resolution at a formal meeting of the City Council.
James C. Hansz, P.E.
Director of Public Works / City Engineer
Attachment: Staff Information
2011"Avenue East, P.O. Box 1997, Kalispel4 MT 59903 —Phone (406) 758-7720 — Fax (406) 758-7831, www.kalispell.com
Memo
To: City Council Members
Re: City of Kalispell's Standards for Design and Construction 2009 Update
Date: September 22, 2009
The City of Kalispell Public Works Department has updated the current Standards for Design
and Construction, which became effective July 2005. The draft 2009 Standards for Design and
Construction was open for Public Comment from February 2, 2009 until March 2, 2009.
Announcements were sent out through fax to over 70 engineers, contractor, and developers. In
addition, Public Service Announcements were placed in the newspaper and on the radio. Public
Works staff reviewed the comments received and made changes to the 2009 draft document
based on some of those comments. A copy of the comments and City responses are included in
the packet.
As was stated in the initial January 30, 2009 memo to Council, the intent of the update is to
incorporate changes in the standards since the last update. Edits were made to each section and a
new section, Stormwater Design Manual, was added to the Standards. The Stormwater Design
Manual Section incorporates updated stormwater design methods, new water quality design
methods (which are required by the State and EPA), and the 2008 Stormwater Facility Plan
Update.
Pages 2 and 3 outline the list of the major edits and additions made to the current July 2005
Standards for the following chapters:
1. General Provision
2. Design Standards
3. Stormwater Design Manual
4. Standard Drawings
Included in this packet for Council to review is a copy of the Standards for Design and
Construction 2009, Public comments and City response, and the January Memo. City staff would
like the opportunity to review the updates and address any question from Council at the
workshop.
The following list outlines the major edits to the July 2005 Standards, minor edits are not
included in the list.
General Provisions:
• GP-11 Pollution Controls: Changes to paragraph one, added Construction Stormwater
Management Permit and details.
• GP-12 Pavement Restoration: Spelled out new paving requirements to adhere to 2006
Addendum to the Montana Public Works Standard Specifications, Fifth Edition, March
2003.
Design Standards:
• DS-01 Design and Development Requirements: In the 61h paragraph changed utility
easement from 5' wide to 10' wide.
• DS-02 Water Systems: Minor engineering items were changed in Water Service Lines,
Valve Box, Minimum Pipe Size, Mechanical Joints Restraints, and Warning Tape.
• DS-3 Sanitary Sewer Systems: For Sewage Lift Station specified an emergency power
requirement and added noise limits. Required an all weather 12-foot minimum width access
road to the lift stations.
• DS-4 Storm Drainage Systems: Moved entire section to Chapter 3 Stormwater Design
Manual.
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• DS-5 Roadways and Walkways: For Cul-de- Sacs changed five foot (5') boulevard to six
foot (6') boulevard.
• Added DS-7 Street Lighting: Specifies in detail lighting standards.
• Added DS-9 Multiple Use Paths: Outlines design standards, path width, and signage
requirements.
Stormwater Design Manual (Added Chapter): The following is a brief section by section
overview of the manual:
• Section 1-Introduction briefly describes the manual's objectives and general requirements.
• Section 2-Basic Requirements introduces seven basic requirements for new development
and redevelopment projects in the City of Kalispell. The applicability of these requirements
depends on the type, size, and location of the project.
o Changed the requirement for drainage report from 10,000 SF to 5,000 SF.
o Added Redevelopment requirements.
o Added Water Quality Treatment requirements.
• Section 3-Drainage Submittal describes the required contents of a Drainage Submittal and
provides a framework for preparing the submittal in order to promote consistency.
• Section 4-Geotechnical Site Characterization outlines the minimum requirements for a
geotechnical site characterization (GSC). A GSC is used in developing recommendations
for stormwater disposal and determining the feasibility of constructing below ground
structures i.e., basements, crawl spaces, infiltration basins.
• Section 5-Hydrologic Analysis and Design provides the tools for estimating peak flow rates
and volumes for sizing conveyance, treatment, and flow control facilities.
• Section 6-Water Quality Treatment Design presents a description of the methodology for
water quality design, and incorporates Water Quality Treatment design standards for
infiltration basins, infiltration swales, wet ponds, biofiltration swales, dry swales,
bioretention facilities, and wetlands.
2
• Section 7-Flow Control outlines the requirements for sizing flow control facilities. It also
sets minimum requirements for flow control facilities including discharge rates,
setbacks, release points, access requirements, draw down time, side slopes, fencing,
landscaping, and maintenance.
o Changed design storm requirement from 10 year 6 hour storm to 10 year 24
hour storm and from 100 year 6 hour storm to 100 year 24 hour storm.
• Section 8-Natural and Constructed Conveyance Systems outlines the requirements for
conveyance systems including all natural or constructed components of a storm drain
system that collects stormwater runoff and conveys it away from structures.
o Added section for the preservation of Natural Drainage Ways (NDW) defined in
the City of Kalispell's 2008 Stormwater Facility Plan Update.
• Section 9-Erosion and Sediment Control Design lists the steps for developing a construction
site Stormwater Management Plan, also known as an Erosion and Sediment Control Plan.
• Section 10-Maintenance, Parcels, and Easements establishes operation and maintenance
responsibilities and procedures for new development and redevelopment projects.
Standard Drawings:
• SD-1 Collector Street: Boulevard width increased from 5 feet to 6 feet.
• SD-2 Local Street: Boulevard width increased from 5 feet to 9 feet.
• SD -13 Manhole and Valve Box Collar: Added standard drawing detailing concrete collar
requirements.
• SD-19 Retrofit Pedestrian Ramp: Added standard drawing detailing retrofits for pedestrian
ramps.
• SD-20 Concrete Curb Inlet Apron: Added standard drawing detailing concrete curb inlet
apron.
• SD-21 and SD-22: Added standard drawing detailing sewer and storm manhole covers.
The responses provided in the matrix below are the City's responses to the verbal and
written comments regarding the 2009 Update Standards for design and construction.
Verbal Comments
Greg Lucasik, P.E., Morrison Maierle Inc 3/10/09
Comment
Response
1
Pg 8 Isolation Valves: the description is
Edited, see standards.
unclear it should state a valve is
required at each leg of the main.
2
Could not locate in the water and sewer
Valves and manhole lies shall not be
sections DS-2 and DS-3 where the
located in the travel way, sidewalks, or
valves should be aligned in the road
curb and gutter. Mains shall not be
way.
located under the sidewalk or curb and
utter.
3
Pg 96, Manning n value for the pipe
PVC =.012, DI =.012 to .015, add note
should be adjusted to: Ductile iron =
n values can be based on
0.15, PVC = .009
manufacturer's recommendations.
Written Comments
Kris Desper, P.E., CTA, 3/9/09
Comment
Response
1
Section 2.1.1 -states that if 5,000 square
Basic requirements outlined in Section
feet of impervious (new or otherwise) is
2 will be triggered with the addition or
constructed, then the basic requirements
replacement of 5,000 sf.
apply (including a stormwater report)
with exceptions as mentioned. Section
DS-04 of Chapter II — Design Standards
states that 10,000 square feet of
impervious is the threshold for a
stormwater report.
2
Section 5 - might want to include the 6
Not needed.
hour precipitation depth for the 2 YR,
10 YR and 100 YR storms. This
information is needed to calculate flows
using the SCS method.
3
Section 6.3.5 - states that bioswale shall
The minimum length requirement for a
be 200 feet long. Maybe it would be
bioswale has been changed to 100 feet.
better to state that the bioswale must be
at least 100 feet long. With the required
contact time of 9 minutes and the large
amount of flow generated by the
snowpack runoff, the size of the
bioswale will be governed by these
parameters.
4
Section 6.3.7 - maybe the addition of the
Noted.
Washington Department of Ecology
website to verify other technologies
approved by the WDOE would be
helpful.
5
Section 7.4.1 - spelling error in sentence
Edit fixed.
"near tip of riser".
6
Also, there is mention of the Stormwater
When referenced in the manual
Quality Management Plan which took
Stormwater Quality Managements Plan
has been underlined to show it is a title.
some time to locate. Since this plan is
connected to the MS4 permit, maybe
some verbiage could be included. I
continued to reference Section 6 of the
Construction Standards before I realized
it was another document.
7
Section 2 — "Water quality treatment is
Basic requirements outlined in Section
required for all development and
2 will be triggered with the addition or
redevelopment projects adding or
replacement of 5,000 sf.
replacing 500 feet of impervious surface
or more." It appears that this is a very
low threshold since the Washington
DOE (which has some of the most
stringent regulations in the U.S.) has a
threshold of 5,000 square feet for
treatment of new impervious surfaces.
It is my understanding that currently
there is a moratorium for the design and
installation of underground detention
structures. As the value of land
increases, underground structures
become more cost effective. Another
advantage is the elimination of unsightly
retention/detention ponds at project sites
and the potential liability associated
with these structures. I have designed
numerous underground vaults and other
detention structures with success
including an underground sand filter
vault. The manhole covers can be bolted
to minimize liability and some cities are
inspecting private underground vaults to
ensure maintenance of the facilities.
Therefore, I would request a review of
this topic and allowance of future
underground structures for stormwater
treatment and detention purposes.
Robert Smith, P.E., A2Z Engineering, 3/2/09
The standards will state underground
detention is not permitted. Under
extreme situations when all other
options have been considered, the
developer can go through the deviation
process outlined in section 2.1.5.
One can assume the City will be held
ultimately responsible for the function
of the facility. In that regard, long term
maintenance and operation of open
stormwater system is more cost
effective for the City.
Comment
Response
1
Section DS-04, Traffic Analysis: I
Agreed, edited in standards.
recommend that preparation of Traffic
Analysis Reports be restricted (under the
same line of reasoning that the
engineering department is using to restrict
those qualified to perform wetlands
analysis or geotechnical analysis) to
professional engineers with a proven
traffic specialty. My suggestion is that
they must be an accredited Professional
Traffic Operations Engineer (PTOE).
This certification guarantees that the
engineer has a minimum of 4 years direct
traffic experience and has taken a national
standard exam. More information can be
found at
http://www.tpcb.org/ptoe/requirements.asp
2
Stormwater Section 1.3: The last sentence
The objective of a Down -Gradient
addresses Down -Gradient Analysis, but is
Analysis is to inventory natural and
very open-ended. The analysis
constructed down -gradient drainage
requirement of following drainage 1/4 mile
features and to identify and evaluate
downstream is too great, and should be
adverse down -gradient impacts that
changed to a percentage of contributed
could result from the proposed project.
flow (such as when the development's
Common adverse impacts of land
contribution becomes less than 10% of the
development include erosion,
flow).
flooding, slope failures, changed
runoff patterns and reduced
groundwater recharge (to springs,
streams, wetlands and wells, etc.).
A Down Gradient Analysis of 1/4
mile down stream analysis meets the
objective goal.
3
Stormwater Section 2.2.2: The GSC is
The GSC under the Basic
needed in far too many situations Linder
requirements outlined in Section 2
this manual. It should only be needed in
will be triggered with the addition or
areas with known issues. The requirement
replacement of 5,000 sf.
inflicts a mandatory $2000 cost upon
every single project that even considers
pouring a new footing. If the issue of wet
basements has provoked this provision, it
should be dealt with utilizing footing
drains, not unnecessarily subsidizing the
two local geotechnical firms.
4
Stormwater Section 2.2.3: The 500 square
Basic requirements outlined in
feet water quality threshold is too low, and
Section 2 will be triggered with the
doesn't coordinate with any other
addition or replacement of 5,000 sf.
numbers. It should be set to match either
The 500 was a typo.
the 5000 square feet storm water threshold
or the 1000 square feet land disturbance
permit threshold. I recommend the 5000
sq ft.
5
Stormwater Table 2-1 and 7-1: The
To better clarify, offsite bypass will
wording of this table creates the
be removed from the statement.
impression that the development is
responsible for reducing off -site by-pass
flow to 50% of it's 2-year rate. If this is
the intent of the requirement, it is
unreasonable.
6
Stormwater Section 2.2.5: The fourth
paragraph may be interpreted (is vague) to
The intent of the paragraph is to
prevent all development since any change
eliminate downstream or adjacent
to a site diverts some form of sheet flow.
property from being impacted from
Except for 100% infiltration facilities, any
new development.
storm water released from the site will
usually be more concentrated (in a new
pipe or swale).
7
Stormwater Section 2.2.5: Culverts
A culvert is a short pipe used to
should be held to the same standard as
convey flow under a roadway or
street drainage facilities, the 10-yr storm.
embankment. Culverts are used to
Mandating the 100-yr for culverts
pass peak flow from defined drainage
confuses the design. Provision can be
ways identified on contour maps.
made by requiring the 100-yr to have a
viable path.
Culverts will be utilized under
roadways to pass the existing
Natural Drainage Ways. Per the
adopted 2008 Facility Plan Update,
the Natural Drainage Ways are
required to pass the 100 year peak
flows to prevent major damage to
transportation systems.
8
Stormwater Section 3.3.2: All areas drain
To better clarify "or is contiguous"
eventually to 100-yr flood zones.
with will be added.
Therefore, the wording of this should be
changed to reflect direct contact with the
100- r flood zone.
9
Stormwater Section 3.4.2: The
Agreed, the section will be revised.
requirement for a Wetland Analysis is a
costly burden to add onto every single
project, when relatively few are actually
going to qualify. Again, maybe some
sensitive areas identified on a city map
would be more reasonable.
10
Stormwater Section 5.3.6: Between the
The ARC III condition will be
NRCS TR20 hydrology, distributed CN
removed from the WQ volume
method, the ARC III conditions, the
calculation.
assumed 1.1" frozen ground snowmelt
runoff, the amount of runoff is being
radically increased compared to previous
requirements. Staff should prepare a
sample cost estimate of a 1 acre project
under the old requirements verses the new
requirements for examination by City
Council, because it will be a major issue.
11
Stormwater Section 6.3.1: It appears that
Changed the requirements for infiltration, see
if an infiltration basin is limited to 2.5
edits in standards.
inches per hour, then has a 48 hour time
A reduction factor of two (2) shall be used
limit and a fairly typical reduction factor
in determining the long-term infiltration
applied of approximately 12, then the
rate below.
maximum depth of infiltration allowed is
10 inches. This is unreasonable because it
An infiltration rate of 0.5 inches/hr to 2.5
automatically requires a ponding area (rain
inches/hr is typical for soil textures that
garden) of tremendous size. Cost becomes
possess sufficient physical and chemical
a major factor when this happens.
properties for adequate treatment. When the
Long-term infiltration rate is greater than
2.5 inches/hr a site specific analysis shall
be performed to determine pollutant
removal to prevent groundwater
contamination.
12
Stormwater Section 7.5: As above,
Same as 11.
because of limits to infiltration rates and
time periods, a 30" tall StormTech
underground chamber (SC-740) will only
get credit for the first 10 inches. This is a
very costly requirement.
t?
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YIUV1UMg Lne equaLlOnS and examples
engineering analysis along standard
is a good tool for engineers to use
methodologies, I think there is too much
when engineering a site project.
explanation of general hydraulics (such as
the gutter flow equations). Regulations
should not try to do the job of general
hydraulic textbooks. A mention of the
method desired would be sufficient. The
engineer's that you are expecting to do
this work should not be learning it from
the regulations. This will help to shorten
the document as well.
Brett Walcheck P.E. 48 North 3/2/09
Comment
Response
1
Chapter 1
Concur with comment: Change to
read...."Unsuitable excavated material
GP-09: I believe the overall intent of
shall not be stockpiled on site without
the standard is understood. I, however,
the express written approval of the
can provide examples of road
Public Works Department."
reconstruction projects where unsuitable
material had to be stockpiled for a short
duration. I would suggest the addition
of a time limit or further language to the
nature of "upon approval from the
Public Works Department".
2 I Chapter 2
DS-03/Sewage Lift Station/2nd
paragraph, pg 11: I am not positive but
this paragraph appears to be addressing
multiple tasks relating to different
subjects. In regard to the influent pipe
being ductile iron, I assume this is
regarding the sanitary flow of the
approach pipe. However I am not sure
why an influent gravity pipe needs to be
ductile iron. If for some reason this is
accurate, shouldn't you then have
further clarification on the pipe material;
for example, it being polyethylene
lined?
3 DS-04: The sidewalks have now been
pushed flush with the ROW. Does this
leave adequate room for the surveyors to
set pins for the bisecting property lines?
In the past that was one of the reasons
0
there was a 1-foot clear zone between
the sidewalks and ROW.
Chapter 3,
Section 1
1.3/1st paragraph, page 21: Please
further clarify how flow can leave the
site in the manner as in pre -developed
conditions after meeting the
requirements stated in the following
sections. Once you collect the water in a
holding facility, it can only exit via
concentrated.
7
The one joint of ductile iron pipe
entrance to the sewage pumping station
wet well maintains a consistent
flowline. Flexible pipe (PVC) tends to
deflect over time as the backfill around
the wet well settles; no matter how well
initially compacted. This deflection
creates a belly in the pipe which could
create maintenance problems in the
future. Severe deflection will cause
rupture of the pipe. The ductile iron
will be specified as Class 50 cement
lined.
The surveyor will have to set a
witness/offset pin to identify where the
actual property bin is located.
The intent of the paragraph is to
eliminate downstream or adjacent
property from being adversely
impacted from new development.
5 1 Section 4
Please note that under Section 1.3, this
manual requires the submittal to be
prepared by a professional engineer,
licensed in Montana. All items defined
in 2.2.2 and 4.1 falls under the
capabilities of a licensed civil engineer.
The City must accept the fact that upon
requiring the certification of the licensed
professional engineer, it also must
accept the multi disciplines granted to a
licensed engineer by the State of
Montana. This section needs to be left
to the discretion of the stamping
engineer to decide whether he or she is
comfortable in generating the entire
GSC or if he or she may need assistance
from a more specialized field.
Agreed, the paragraph now reads: A
CD
professional engineer currently
licensed in the State of Montana is
required to perform the GSC.
6 I Section 5
The proper way to fully understand any
proposed changes is to be able to apply
it in practice. Obviously when this
occurs it will be too late to make any
proper comments on the proposed
standards. The adoption of the SCS
method is a deviation from the standard
practice applied by many of the local
engineers and typical state practices. It
is not to say that it is an unacceptable
method, it is just only one of the
methods available to engineers. I
personally do not believe it is a good
engineering practice to limit the tools
available to engineers, especially when
these tools have years of established
history. An example is the Rational
Method; this method is widely accepted
and typically leans more on the
conservative side of the SCS. I believe
the Montana Department of
Transportation summarizes it best when
it states: Even though it (Rational
Method) comes under criticism for its
simplistic approach, no other drainage
design method has received such
widespread use.
11
Unfortunately, "widespread use" does
not mean a design resulting in
acceptable results for stormwater
quality protection and determining
more accurately urban impacts on
runoff volume.
The Rational Method (commonly
attributed to Mulvany, 1851) was
developed in the 1800's to estimate
peak flow rate (Q) of flood events. The
Rational Method wasn't developed to
determine runoff volume or adequately
deal with modeling runoff during
smaller storm events that drive so much
of the stormwater quality issues. That's
not to say that many haven't warped the
model into other uses. However, with
the advent of computer based
hydrologic modeling software in the
last century and improved models, the
Rational Method is best left to its most
common application - sizing storm
drainage pipe.
The SCS Method is the technically
correct method for calculating the
runoff volumes and therefore is
required for the design.
7
Section 7
The standards will state underground
detention is not permitted. Under
It appears that everything in regard to
extreme situations when all other
infiltration and detention facilities are
options have been considered, the
based off the application of open pond
developer can go through the deviation
facilities. Although I could not find
process outlined in Section 2.1.5 on
direct language stating that underground
page 23.
facilities were not allowed, I also could
not find any language stating they were
One can assume the City will be held
acceptable. However my assumption,
ultimately responsible for the function
based on previous discussions, is that
of the facility. In that regard, long term
the City will not be accepting them. I
maintenance and operation of open
believe there are specific times when an
stormwater system is more cost
underground facility is better suited for
effective for the City.
the project. With the adoption of these
standards many developments are going
to require the need for significant space
to accommodate stormwater
management. Some sites physically do
not have the above ground surface
available; however have ample under-
ground space available. I do not believe
it is fair to the landowners to either have
to purchase additional land or rearrange
their site when there are alternative
methods that could have been
implemented.
8
Doug Peppmeier, P.E., TD&H , 3/3/09
Comment
Response
1
DS-02 Water Systems and
Agreed, the section will be edited.
DS-03 Sanitary Sewer Systems
Both of these sections reference the old
Montana Dept. of Health and
Environmental Sciences WQB standards
instead of the current DEQ Design
Circulars.
10
2
M
5
DS-03 Sanitary Sewer Systems and
Sect. 8.7.1 Structures
I tried to find the cut sheets/details for
the new manhole rings and covers (both
sanitary and storm) but could not find
any information for the East Jordan Iron
Works product no. NCR07-1738A or
the Olympic Foundry part no. 11-3804.
Are these the correct product/part
numbers?
Sect. 2.2.3 Applicability
Under applicability, the manual
references "projects adding or replacing
500 square feet of impervious service or
more." Should this number be 5,000
square feet in order to be consistent with
Section 2.1.1.
Sect. 2.2.3 Design Criteria
Talks about stream and river flow
control standards. It seems like this
should be covered in the flow control
design sections?
Sect. 7.3.1 Discharge Rates
Table 7-1 (Allowable Discharge Rates)
states that for the 2-yr. design event the
allowable post -developed discharge rate
is less than or equal to 50% of the pre -
development rate. This seems like an
impossible requirement to meet due to
the small flows and it doesn't make
sense that you would have to reduce the
existing runoff from a natural site by
half after development. It seems like the
requirement should be to meet the 2-yr.
pre -developed rate.
11
East Jordan Iron Works product no.
NCR07-1738A or the Olympic
Foundry part no. 11-3804, refer to the
Kalispell stamped covers. Contact the
manufacture to get the specifications. A
copy will be included in the standards.
Basic requirements outlined in Section
2 will be triggered with the addition or
replacement of 5,000 sf. The 500 was a
typo.
It is covered in both sections
Research has shown that urban
development appears to impact streams
at very low thresholds (5 — 15%
impervious). Typical standards of rate
control haven't proved successful at
protecting urban streams (Booth, 1997)
or mitigating urbanization greater
impact on frequent events than on rare
(flood) events (Fennessey, 2001).
Hence, we chose to implement a water
quality rate control rule of 50% of
existing 2-year runoff rate based
research recommendations by Booth
and following stormwater standards
developed for Eastern Washington by
the Washington Dept. of Ecology.
6
Sect. 7.4.1 Multiple Orifice Restrictors
Both a 2" and 3" orifice are very small
This section states that the minimum
and are likely to plug more than a larger
orifice diameter is 3 inches. When
diameter. A 3" will remain the
trying to meet the post -developed 2-yr.
minimum and suggest the basin size be
flow requirement using a 3" orifice will
adjusted as needed using skimmer
be very difficult because the orifice
designs Fig. 7.4 & 7.5.
restrictor will most likely let too much
water out even with a small amount of
head. Seems like a 2" min. would be
more appropriate and would still be
large enough to guard against blockage.
7
Detail SD-11 Vehicle Tracking Control
Edited standard.
The type of rock/stone specified in the
current detail is called out as "4-8 inch
stone". We have seen a lot of local
contractors using rounded rock in these
applications which completely defeats
the intent of the tracking pad and an 8"
stone seems a little large. I would
suggest changing the requirement to 2-
3 11 clean pit run, 2-4" quarry
spalls or gravel material. I think the key
is to have an angular material with some
voids ace.
12
Andy Hyde, P.E., Carver Engineering, 3/2/09
Comment
Response
1
The existing design standards for
Due to the high development in the City of
storm drainage systems comprise a
Kalispell a revision of the standard was
total of 17 paragraphs on less than
needed to update the standard and implement
2 pages in the City's Standards for
State permit requirements.
Design and Construction
Handbook. The proposed new
guidelines have expanded at least a
hundredfold and it takes two
separate documents to hold them.
The first document — the
Stormwater Quality Management
Plan — contains 91 pages. The
second booklet — Chapter I11, the
Kalispell Stormwater Design
Manual — contains 134 pages. The
total number of pages in the City's
proposed new storm water plan and
standards are 225. One can read
this material now and understand
what every page says, but the true
meaning and impact of these new
guidelines and standards can't be
really known until a designer has
applied them to many actual
designs and can compare the
finished product of these
regulations with previous versions.
2
The City of Kalispell will have the
Developing consistent methodology and
obligation to implement and
procedures, the review process will be more
administer these regulations and
efficient.
review proposed new designs for
conformance. The sheer volume of
information required by the new
regulations guarantee that designs
will be more complex and that the
City review process will be
lengthy.
13
3 The new regulations were lifted from other
jurisdictions and unfortunately, to our
knowledge, the City staff has no experience
designing projects on their own using these
proposed new regulations even though City
reviewers should be familiar with the nuances
of the regulations and will be required to apply
a considerable amount of critical judgment
during review. Without actual hands-on design
experience, the City staff is as ignorant as the
local design community about actual
implementation of the proposed new
regulations.
There is a solution. The City of Kalispell
operates many existing storm water systems
that, using a term from the City's recently
finished Stormwater Facility Plan update, "do
not correlate with" the proposed new
Sormwater standards. The City of Kalispell
should undertake a demonstration project prior
to implementing these proposed new
guidelines. The good opportunity for all to
develop an understanding of these regulations
from both the designer's and owner's
perspectives is for the Kalispell staff to design
in-house a model retrofit nroiect on one of the
City's existing storm water systems.
The engineering community should be allowed
to participate or at least observe as design,
review and construction of this new system
proceeds so that they too can learn the realities
of the new regulations. Once the finished
project is in operation, the value of the new
standards could be objectively determined by
comparing before and after water quality
samples of water discharged from the system.
It will be interesting to see if the hundredfold
increase in the volume of the regulations results
in a hundredfold increase in water quality.
In any case, the experience will allow
participants to learn the strengths and
weaknesses of the proposed new regulations
and the regulations can be revised (improved)
based upon this project. The true cost of the
requirements can also be compared with water
quality improvements to see if the changes are
worth it. It the City is spending its own money;
the exercise will be much more meaningful to
City officials.
City staff has processional experience in
designing projects and feels confident the
review of projects will be sufficient to meet
the standards implemented.
Since 2006 multiple development sites
throughout the City have incorporate the
Water Quality Design methods outlined in the
2009 Standards update.
14
7
The proposed regulations restrict
Additional BMPs for water quality treatment
new stormwater systems to just a
have been added to the standards.
few alternatives, all of which tend
to concentrate stormwater in
Low Impact Development (LID) is a process
centralized areas and encourage
of developing land to mimic the natural
low impact designs for stormwater
hydrologic regime. It incorporates land
facilities as these LID systems are
planning and design practices and
proven to be both effective and
technologies to achieve this objective. LID
economical.
begins at the design phase of a new
development, incorporating planning
techniques to minimize site clearing and
impervious surfaces. The City strongly
encourages the use of LID measures. LID
helps reduce stormwater impacts by
minimizing developed and impervious areas
on a site and through the incorporation of
runoff storage measures dispersed throughout
a site.
Infiltration and Bioretention are considered
LID Techniques. Other
LID practices, i.e. minimizing impervious
areas, will have to be initiated by the
developer or the developers' engineers.
8
There is an economic dimension of
The stormwater management for the
the new regulations. We have been
referenced project site is based on decisions
working with the Kalispell Public
made by the engineer and the developer.
works staff to include storm water
systems conforming to these new
The project site layout could have used the
proposed regulations in a potential
sites natural hydraulic amenities to develop a
future subdivision containing 200
stormwater management system which could
lots on a total of 35 acres for the
have potentially reduced the required area.
lots. The necessary number of
City Staff also worked with the engineer to
stormwater systems for this
incorporate the stormwater system into the
development is 13 different
open space/park area and therefore reducing
systems on a total of 6 acres. The
the stormwater management areas. To our
new regulations reduce the number
knowledge, neither one of those options were
of lots by 17% of the total available
used by the developer or the developer's
lot area. A total of 34 lots would
engineer.
be lost in the process.
15
201 P Avenue Eas4 P.O. Box 1997, Kalispell, MT 59903 —Phone (406) 758-7720 — Fax (406) 758-7831, www.kalispell.com
1kV rVire
To: City Council Member
Re: City of Kalispell's Standards for Design and Construction 2009 Update
Date: January 30, 2009
The City of Kalispell Public Works Department is in the process of updating the current
Standards for Design and Construction which became effective July 2005. The draft 2009
Standards for Design and Construction will be open for Public Comment until March 2, 2009.
The draft Standards provide updates in the following Chapters:
1. General Provision
2. Design Standards
3. Stormwater Design Manual (new chapter)
4. Construction Standards
5. Standard Drawings
The intent of the update is to incorporate changes in the standards since the last revision. The
new chapter, Stormwater Design Manual, was added to the standards to incorporate updated
stormwater design methods, new water quality design methods which are required by the State,
and the 2008 Stormwater Facility Plan Update. The new water quality design methods meet the
State General Permit for Storm Water Discharge Associated with Small Municipal Separate
Storm Sewer Systems (MS4) permit requirements. A Stormwater Quality Management Plan
was developed in corporation with the 2008 Facility Plan Update to provide stormwater quality
technical information and methodology to meet MS4 permit objectives. Information from this
plan was then used to develop the new water quality design methods. A summary of the MS4
permit requirements and incorporations are included on pages 2 to 5.
Included in this packet is a copy of the draft Standards for Design and Construction 2009 and
the Stormwater Quality Management Plan.
Chapter 3: Stormwater Design Manual Review
In the past three years the City of Kalispell has expanded its boundaries by 3.23 square miles.
With growth comes added responsibility for the City to manage stormwater discharges within its
boundaries. The State General Permit for Storm Water Discharge Associated with Small
Municipal Separate Storm Sewer System (MS4) authorized the City, in 2006, to discharge
stormwater to waters of the State. In receiving authorization, the City is responsible for
implementing MS4 permit conditions and requirements. The MS4 permit required the City to
develop a Stormwater Management Program that addressed six minimum control measures. The
minimum measure Post -Construction Storm Water Management in New Development and
Redevelopment is the measure prompting the development and implementation of the
Stormwater Quality Management Plan and Chapter 3: Stormwater Design Manual.
The minimum measure Post -Construction Storm Water Management in New Development and
Redevelopment has multiple requirements. The following is a brief description of the permit
requirements and correlating City programs that address each condition.
Permit Requirement l:
Develop, implement, and enforce a program to address stormwater runoff from new development
and redevelopment projects that discharge into the permitted small MS4. This program must
ensure that controls are in place that would prevent or minimize water quality impacts. Identify
how the program will be specifically tailored to the local community, minimize water quality
impacts, and maintain pre -developed runoff conditions:
a. City's response: Chapters 1 through 5 in the Stormwater Quality Management Plan
developed goals and policies, characterized waterbodies in the Kalispell study area,
outlined urban development impacts to waterbodies, and characterized Kalispell's
annual precipitation events.
Permit Requirement 2:
Develop and implement strategies that include structural Best Management Practices (BMPs)
appropriate for the community. Identify storage and treatment practices such as: 1) wet ponds
and extended -detention outlet structures, 2) filter practices, and 3) infiltration practices such as
infiltration basins and trenches.
a. City's response: Chapters 6 and 7 in the Stormwater Quality Management Plan
outline flow control standards, water quality volume standards, and guidance for the
selection and design of permanent stormwater quality treatment facilities (i.e.
structural BMPs).
b. City's response: Sections 6 and 7 in Chapter 3: Stormwater Design Manual
integrates the water quality treatment standards and flow control standards from the
Stormwater Quality Management Plan and provide design guidelines for BMPs.
Permit Requirement 3:
Develop and implement strategies that include non-structural Best Management Practices
(BMPs) appropriate for the community. Identify policies and ordinances that provide
requirements and standards that directs growth to identify waterbodies, protect sensitive areas
such as wetland and riparian areas, maintain and/or increase open space, provide buffers along
N
sensitive waterbodies, minimize impervious surface, and minimize disturbance of soil and
vegetation.
a. City's response: Chapter 3 in the Stormwater Quality Management Plan
characterized the waterbodies within the Kalispell study area and establishes an on -
site wetland assessment procedure to be performed on new development and
redevelopment projects.
b. City's response: Section 10 in Chapter 3: Stormwater Design Manual addresses
non-structural BMPs by establishing operation and maintenance responsibilities and
procedures for new development and redevelopment.
Permit Requirement 4:
Use an ordinance or other regulatory mechanism to address post -construction runoff from new
development and redevelopment projects to the extent allowable under State, Tribal or local law.
a. City's response: The standards and policies developed in both Chapter 3:
Stormwater Design Manual and Stormwater Quality Management Plan are the
regulatory mechanisms that address post -construction runoff for new development
and redevelopment.
Permit Requirement 5:
Ensure adequate long-term operation and maintenance of BMPs. identify how the long-term
operation and maintenance (O&M) of the selected BMPs will be ensured. Ensure that future
O&M responsibilities are clearly identified including an agreement between the permittee and
another party such as the post -development landowners or regional authorities.
a. City's response: Section 10 in Chapter 3: Stormwater Design Manual addresses
stormwater management systems operation and maintenance responsibilities and
procedures for new development and redevelopment.
The Stormwater Quality Management Plan was developed to address and minimize water quality
impacts from new development and redevelopment projects. The new policies and standards
developed in the Stormwater Quality Management Plan do not correlate to the current
stormwater standards in the July 2005 City of Kalispell Standards for Design and Construction.
In 2008, City consultants completed the 2008 Stormwater Facility Plan Update.
Recommendations developed from the update also do not correlate to the 2005 standards.
Chapter 3: Stormwater Design Manual incorporates the Stormwater Quality Management Plan,
the 2008 Stormwater Facility Plan Update, and design methods and standards into a single
document. This new manual not only addresses the MS4 permit requirements, but will provide
planners, engineers, developers, and the general public with procedures and assistance for
designing stormwater management systems. The following is a brief section by section overview
of the manual:
Section 1-Introduction briefly describes the manual's objectives and general requirements.
Section 2-Basic Requirements introduces seven basic requirements for new development and
redevelopment projects in the City of Kalispell. The applicability of these requirements depends
on the type, size, and location of the project. The seven basic requirements are:
• Basic Requirement No. 1 — Drainage Submittal
• Basic Requirement No. 2 — Geotechnical Site Characterization
• Basic Requirement No. 3 — Water Quality Treatment
3
• Basic Requirement No. 4 — Flow Control
• Basic Requirement No. 5 — Natural and Constructed Conveyance Systems
• Basic Requirement No. 6 — Erosion and Sediment Control
• Basic Requirement No. 7 — Operation and Maintenance
The trigger for requiring compliance with the basic requirements set in the manual is defined as
the addition or replacement of 5000 square feet or more of impervious area. The applicability
and design criterion for each basic requirement is further described in this section and the
following sections.
Section 3-Drainage Submittal describes the contents of a Drainage Submittal and provides a
framework for preparing the submittal in order to promote consistency.
A Concept Drainage Report package is required at the pre -application stage and before
preliminary plat approval. The purpose of the Concept Drainage Report is to demonstrate that
the proposed drainage facilities can meet the intent of the manual and are feasible with respect
to design, constriction, and maintenance. Its contents are similar to those of the Drainage
Report.
A Drainage Report is required with the project engineers report as defined in the Construction
and Design Standards. The purpose of the Drainage Report is to identify drainage impacts
resulting from land development activities and determine the improvements necessary to control
the increase in stormwater runoff and to treat the pollutants that can adversely impact water
quality. The manual provides a list of drainage elements, figures, calculations, and analysis that
shall be included in the Drainage Report submittal.
Section 4-Geotechnical Site Characterization outlines the minimum requirements for a
geotechnical site characterization (GSC). A GSC is used in developing recommendations for
stormwater disposal and determining the feasibility of constructing below ground structures (i.e.
basements, crawl spaces).
Section 5-Hydrologic Analysis and Design provides the tools for estimating peak flow rates
and volumes for sizing conveyance, treatment, and flow control facilities.
Section 6-Water Quality Treatment Design presents a description of the methodology for
water quality design, and incorporates BMP design standards from the Stormwater Quality
Management Plan.
Section 7-Flow Control outlines the requirements for sizing flow control facilities. It also
sets minimum requirements for flow control facilities including discharge rates, setbacks,
release points, access requirements, draw down time, side slopes, fencing, landscaping and
maintenance.
Section 8-Natural and Constructed Conveyance Systems outlines the requirements for
conveyance systems including all natural or constructed components of a storm drain system
that collects stormwater runoff and conveys it away from structures. Conveyance facilities consist
of curbs and gutters, inlets, storm drains, catch basins, channels, ditches, pipes, and culverts.
M
This section also introduces the preservation of Natural Drainage Ways (NDW) defined in the
City of Kalispell's 2008 Stormwater Facility Plan Update. New developments shall be
designed to protect existing natural drainage features that convey water, store water, or allow
water to infiltrate into the ground in its natural location. Preserving the NDW will help ensure that
stormwater runoff can continue to be conveyed and disposed of at its natural location.
Section 9-Erosion and Sediment Control Design lists the steps for developing a construction
site Stormwater Management Plan, also known as an Erosion and Sediment Control Plan
(ESC). The City of Kalispell's Construction Site Stormwater Management Ordinance 1600 went
into effect May 2, 2007. This section outlines the standards set in the ordinance and suggests
BMPs to be used during construction site activities.
Section 10-Maintenance, Parcels, and Easements establishes operation and maintenance
responsibilities and procedures for new development and redevelopment projects. This section
also describes maintenance access requirements, stormwater facilities and systems locations within
parcels and easements.
5
CITY OF KALISPELL
STANDARDS FOR DESIGN AND CONSTRUCTION
4iJuly 2009
STANDARDS FOR DESIGN AND CONSTRUCTION
CHAPTER I
GENERAL
PROVISIONS
Page Number
GP-01
Standards...........................................................................................................................1
GP-02
Public Right -of -Way Perrnit.............................................................................................1
GP-03
City Fees...........................................................................................................................1
GP-04
Applicable Laws and Indemnification of City.................................................................2
GP-05
Interruption of Service......................................................................................................2
GP-06
Traffic and Pedestrian Control.........................................................................................2
GP-07
Liability Insurance and Bonding......................................................................................3
GP-08
Maintenance Bond for New Infrastructure.......................................................................3
GP-09
Excavation & Disposal of Material From Existing Right -of -Way
& Easement .............. 4
GP-10
Survey Monumentation .........................................................................................4
GP -II
Pollution Controls...................................................................................................4
GP-12
Pavement Restoration....................................................................................................... 5
GP-13
Storm Water Discharge Permit.........................................................................................6
GP-14
Construction Inspection....................................................................................................6
GP-15
Guarantee for Equipment, Materials and Work-nanship..................................................6
GP-16
Stop Work Order...............................................................................................................6
GP-17
Relocation of Utilities......................................................................................................6
STANDARDS FOR DESIGN AND CONSTRUCTION
CHAPTER II
DESIGN STANDARDS
Page Number
DS-01 Design and Development Requirements..........................................................................
7
DS-02 Water Systems..................................................................................................................
8
DS-03 Sanitary Sewer Systems....................................................................................................9
DS-04 Roadways and Walkways...............................................................................................12
TABLE 1 Road Design Standards for Local Subdivision Streets ..............................................
14
DS-05 Driveways.......................................................................................................................15
DS-06 Placement of Utilities.................................................................................................
15
DS-07 Street Lighting ...................................... ...................................................................
15
DS-08 Utility Easements ............................. .......................................................................
17
DS-09 Multiple Use Paths .................. ..............................................................................
17
CHAPTER III
4;
Page Number
STORMWATER DESIGN MANUAL........................................................
..18-146
CHAPTER IV
CONSTRUCTION STANDARDS
Page Number
C 5-01 Project Requirements....................................................................................................
147
CS-02 Construction Standards.................................................................................................147
CS-03 Construction Inspection, Testing, and Quality Control................................................147
CS-04 Record Drawings and Project Acceptance....................................................................
149
CS-05 Two Year Guarantee Inspection....................................................................................
149
CS-06 Boulevard Landscaping.................................................................................................
149
STANDARDS FOR DESIGN AND CONSTRUCTION
CHAPTER V
STANDARD DRAWINGS
Page Number
SD-1
Collector Street...............................................................................................................150
SD-2
Local Street.....................................................................................................................
151
SD-3
Rural Road......................................................................................................................152
SD-4
Alley...............................................................................................................................153
SD-5
Curb and Gutter..............................................................................................................154
SD-6
Driver Over Curb & Gutter...........................................................................................155
SD-7
Straight Curb..................................................................................................................
156
SD-8
Sidewalk........................................................................................................................157
SD-9
Driveway Detail for Curb & Gutter...........................................................................
158
SD-10
Driveway Detail for Straight Curb ......... .............................................................159
SD-11
Vehicle Tracking Control.............................................................................................
160
SD-12
Storm Drain & Sanitary Sewer Service Connections...................................................
161
SD-13
Manhole & Valve Box Collar.......................................................................................162
SD-14
Water Service Line.......................................................................................................
163
SD-15
Typical Utility Trench..................................................................................................
164
SD-16
Street Signs...................................................................................................................
165
SD-17
Street Intersection Gutter.............................................................................................
166
SD-18
Pedestrian Ramp...........................................................................................................
167
SD-19
Retrofit Pedestrian Ramp..............................................................................................
168
SD-20
Concrete Curb Inlet Apron...........................................................................................
169
SD-21
00377163 Manhole Cover............................................................................................
170
SD-22
00377162 Manhole Cover............................................................................................
171
CHAPTER I
GENERAL PROVISIONS
GP-01 Standards.
The latest published edition of the Montana Public Works Standard Specifications are adopted in their
entirety, except as amended by the latest edition of the City of Kalispell Standards for Design and
Construction. With respect to the design and/or construction of public facilities, any conflict(s) or
difference(s) between the Montana Public Works Standard Specifications, the City of Kalispell
Subdivision Regulations, and the City of Kalispell Standards for Design and Construction shall be
resolved in favor of the City of Kalispell Standards for Design and Construction.
New construction will be built under the Standards for Design and Construction in effect at the time of
construction. Any conflicts with the Standards in place at the time the plans were approved can be
resolved on an individual basis.
GP-02 Public Right -of Way Permit. (Excavation Permit)
All construction, excavation or other work on public or private property which will necessitate the use
of the public right-of-way or easement shall require a Public Right -of -Way Permit issued by the Public
Works Department. The work authorized by the Permit icludes, but is not limited to, street
construction and repair, water, sewer, and storm system construction and repair, utility connections
and repair, landscaping, sidewalk, curbing and driveway construction and repair. Also included are any
other uses of the public right-of-way where there is a possibility of creating a hazard. Examples of
hazards are scaffolding, storage of materials or equipment, crane and equipment operations,
demolition, sandblasting and painting operations, temporary construction or demolition dumpster
placement and any other use deemed a haVrements
by the Public Works Department. The Permit will not be
issued until all insurance and bonding req have been met.
In an emergency which requires repairs to be made immediately, the Contractor may excavate and
complete the repairs without first having obtained a Permit. Prior to beginning work at the site during
normal working hours, the Contractor shall notify the Public Works Department at 758-7720. Prior to
beginning work after hours, the Contractor shall notify police dispatch at 758-7780. In either case, the
Contractor shall describe the circumstances and provide the location of the emergency repairs. The
Contractor shall obtain the Permit no later than the next scheduled City work day.
All provisions of the Standards for Design and Construction for the City of Kalispell, Montana, shall
be complied with regardless of the circumstances of the construction.
All steel tracked equipment operating within a public street right-of-way shall be fitted with triple
grouser street pads. The Contractor shall be responsible for damages to City infrastructure within the
public street right-of-way.
GP-03 City Fees.
Water & Sewer Service Connection Fee. A connection fee shall be paid for the connection of each
new water and sewer service to the system. This fee must be paid even if a service line has previously
been stubbed to the property line or other accessible location. Connection fees for water and/or sewer
must be paid before a Building Permit will be issued by the Building Department.
Construction of Water Service. When it is necessary to tap an existing water main for a service
connection, the City will provide the equipment, labor and materials required to tap the main, install
the service line from the main to the service valve, install backfill, and restore the pavement surface.
The City will charge the Owner for equipment, labor and materials required to complete the work. The
Owner will be responsible to construct the service line from the service valve to the point of service.
Construction of Sewer or Storm Service. When it is necessary to tap an existing sewer or storm main
for a service connection, the Contractor will provide the equipment, labor and materials required to tap
the main, install the service line from the main to the point of use and restore the public right of way to
the pre -construction condition.
GP-04 Applicable Laws and Indemnification of City.
The Contractor shall give all notices and comply with all federal, state and local laws, ordinances and
regulations affecting the conduct of the work, and shall indemnify and hold harmless the City against
any claim or liability arising from, or based on, the violation of any such law, ordinance, regulation,
etc., whether by himself or his employees.
GP-05 Interruption of Service.
Any construction that will interrupt the normal operation of city sewer, water or transportation
facilities requires notification of affected City departments and property owners and/or residents. The
Contractor shall notify the Kalispell City Police and Fire Departments at least forty-eight (48) hours
prior to any street closures. All street closures or interruptions of utility services will require the
Contractor to provide a news release speci ing the location of construction and the duration of the
closure. The Contractor shall present the ews release to the news media at least two (2) work days
prior to the beginning of any construction activity. The Contractor shall also notify utility users
affected by the interruption of the type and duration of the interruption at least forty-eight (48) hours
prior to beginning construction.
In the event of an emergency interruption, the Contractor shall notify the Public Works, Police and
Fire Departments as quickly as possible. The Contractor shall immediately dispatch members of his
staff to notify affected individuals by telephone or personal contact.
GP-06 Traffic and Pedestrian Control.
A Traffic and Pedestrian Control Plan shall be submitted and approved by the Public Works
Department for all work within the public right-of-way. The latest edition of the Manual on Uniform
Traffic Control Devices (MUTCD) shall be followed to create the Plan. The location and description
of all Traffic and Pedestrian Control Devices shall be shown on the plan. All signs, except "Stop"
signs, shall comply with the MUTCD for size, type, placement, material and reflectivity. "Stop" signs
shall be 30". The plan must be approved prior to beginning construction. If the required devices are
not in place, the Contractor will not be allowed to begin work on the project. All devices shall be kept
in place and maintained in good visible condition throughout the project. The Public Works
Department reserves the right to reject any device observed to be in substandard condition. Emergency
2
access to the work area shall be maintained at all times.
All barricades and obstructions shall be protected at night by suitable signal lights which shall be kept
illuminated from sunset to sunrise. Barricades shall be of substantial construction and shall be
constructed to increase their visibility at night. Suitable warning signs shall be placed and illuminated
at night to show in advance where construction, barricades or detours exist.
If flagging is required it shall be accomplished by competent and properly equipped flag persons.
Flagging shall be accomplished as described in the Montana Department of Transportation Flagger s
Handbook and the MUTCD.
Traffic control devices shall be removed from visual contact with the traveling public when they are
not being used for the construction activities.
The Contractor shall remove all traffic and pedestrian control devices within 24 hours of the
conclusion of the project construction.
If the Contractor fails to maintain the Traffic and Pedestrian Control Devices in accordance with the
approved plan, the City reserves the right to correct the ciency and all labor, equipment, material
and administrative costs will be billed to the Contractor
GP-07 Liability Insurance and Bonding.
Liability Insurance for Work Within Existing Public Right -of -Way and/or Easement. The Contractor
shall procure and maintain, at the Contractor's expense, during the construction period, Contractor's
Liability Insurance in accordance with the Supplementary Conditions to the General Conditions of the
Montana Public Works Standard Specifications.
All construction work within the public right-of-way or easement (sidewalk and curb construction,
storm drainage and sanitary sewer service line installation, repair, etc.) will require the Property
Owner/Contractor to provide the City with a Performance Bond. The bond shall be equal to the value
of the project and shall remain in force for one year. Contractors furnishing the City with an annual
bond of $5,000 will not be required to furnish additional bonding if the $5,000 bond meets the
requirements of these standards.
Bonds may be in the form of a Surety Bond, a Certificate of Deposit (CD), a Certified Check or an
irrevocable Letter of Credit issued by a bank licensed to do business in the state of Montana.
GP-08 Maintenance Bond for New Infrastructure.
As a condition precedent to the filing of a final plat, the Property Owner, Developer, or Contractor
shall provide the City with a Maintenance Bond of twenty per cent (20%) of the total value of the
public infrastructure constructed within the subdivision, development, or phased development. The
Maintenance Bond shall remain in full force for a two year period after acceptance of the entire City
infrastructure by the City for maintenance. The City expressly reserves the right to draft the
Maintenance Bond for repairs not completed by the Property Owner, Developer, or Contractor within
thirty calendar days of being advised that repairs are required.
The Commencement Date for the Maintenance Bond shall be the date set for the completion of the
required improvements as stated in the Subdivision Improvements Agreement, the date of Substantial
Completion as certified by a Professional Engineer, or the date Final Plat is granted, whichever is
later. If the expiration date of the Maintenance Bond falls after November 16, the expiration date of
the Maintenance Bond shall be June 30 of the following year.
Maintenance bonds may be in the form of a Surety Bond, a Certificate of Deposit (CD), a Certified
Check or an irrevocable Letter of Credit issued by a bank licensed to do business in the state of
Montana.
GP-09 Excavation and Disposal of Material from Existing Public Right -of -Way and Easement.
All material unsuitable for trench backfill, sub -base or base construction, excavated from the
developed public right-of-way or easement shall be removed from the site and disposed of by the
Contractor. The disposal site shall meet regulatory provisions for disposal of the unsuitable excavated
material. Unsuitable excavated material shall not be stockpiled on site without the written approval of
the Public Works Department. Excavated material shall be confined to the work zone as established
during the preconstruction conference or as shown in the contract documents.
All steel tracked equipment operating within a public street right-of-way shall be fitted with triple
grouser street pads. The Contractor shall be responsible for damages to City infrastructure within the
public street right-of-way.
GP-10 Survey Monumentation.
When a street is to be reconstructed, prior to any excavation, a thorough search shall be made for
existing intersection monuments. If found, such monuments shall be perpetuated by standard survey
methods including referencing to at least three (3) accessories such as a chiseled "x" on a storm drain
hood, fire hydrant base bolt, fire hydrant operating nut, drilled hole in curb, or property pin.
Monumentation. Monuments shall be a minimum 5/8" diameter rebar or drivable metal rod, at least
18" long. The monument shall be capped with a brass or aluminum cap identifying the responsible
land surveyor with name and number. The cap shall be recessed at least 1/8" below the final asphalt
surface. Monument risers w/lids of the same type as city water valves (six inches inner diameter) may
be used. The City will provide a riser and lid if given a minimum of three (3) days notice prior to
setting if stocks are available. The monument must fall within City limits.
GP-11 Pollution Controls.
The Contractor shall be responsible to maintain the construction site and all haul routes in accordance
with the requirements of the City of Kalispell's Emission Control Plan (see City Ordinance No. 1139).
The Contractor shall obtain an Air Quality Construction/Demolition Permit prior to beginning
construction. The Contractor shall obtain a Construction Stormwater Management Permit for land
disturbance in the City of Kalispell.
No sediment laden or polluted water shall be discharged off any construction or building site. A City
Construction Stormwater Management Permit for construction sites is required for land -disturbing
4
activities which include, but are not limited to, excavation, planting, tilling, and grading, which
disturbs the natural or improved vegetative ground cover so as to expose soil to the erosive forces of
rain, stormwater runoff or wind. All installations and maintenance of franchise utilities such as
telephone, gas, electric, etc., shall be considered land disturbing activities.
The following land -disturbing activities require a City Stormwater Management Permit:
• Any activity where the total volume of material disturbed, stored, disposed of or used as fill
exceeds five (5) cubic yards; or,
• Any activity where the area disturbed exceeds one thousand (1000) square feet provided it does
not obstruct a watercourse, and is not located in a floodplain.
The Construction Stormwater Management Plan shall adhere to Ordinance 1600 and be submitted
prior to any land -disturbing activity. For detailed information on the City Stormwater Management
Permit refer to Chapter III - STORMWATER DESIGN MANUAL.
GP-12 Pavement Restoration.
The Contractor signing the Public Right -of -Way Permit shall be responsible for pavement
replacement. The Contractor shall restore all surfaces w' i fourteen calendar days after completing
the backfill work.
All new roads or reconstructed roads shall be paved wi a,minimum of 4"of Type B asphalt and shall
be accomplished in accordance with Section 02510 Part 1 through Part 3 of the 2006 Addendum
to the Montana Public Works Standard Specifications, Fifth Edition, March 2003
The pavement restoration shall match the pavement structure thickness as shown on Standard
Drawings SD-1 through SD-4. All excavations within 36" of the edge of the asphalt shall require
removal and replacement from the edge of asphalt to the excavation edge. Asphalt patch areas that fall
within the wheel path of the vehicular travel lane shall be increased in size to the center of the lane or
adjacent lane. In no circumstance will the edge of a patch area be allowed to fall within the wheel
path. Any damage to the existing asphalt surface caused by the Contractor's operations shall be
repaired at the expense of the Contractor, including but not limited to gouges, scrapes, outrigger
marks, backhoe bucket marks, etc. A slurry seal type covering will be considered the minimum repair.
The Contractor shall be responsible for maintaining the area in a smooth and drivable condition until
the permanent pavement is placed. If the ground is frozen, the road cut shall be temporarily repaired
with a minimum thickness of two (2) inches of cold patch material. The temporary repair shall be
maintained by the Contractor for safe winter usage. The permanent restoration shall be made as soon
as the ground is thawed in the spring, or as directed by the Public Works Department. Pavement
repairs shall be in accordance with the Standards for Design and Construction.
If the Contractor fails to restore the pavement within the fourteen day period, or fails to maintain the
trench or area as required, the City reserves the right to complete the restoration or maintenance, and
all labor, equipment, material and administrative costs will be billed to the Contractor.
s
GP-13 Storm Water Discharge Permit.
No sediment laden or polluted water shall be discharged off any construction or building site. The
requirements contained within Chapter III Kalispell Stormwater Design Manual shall be followed for
all land disturbance activities within the City of Kalispell.
GP-14 Construction Inspection.
Maintenance and repair work within public right-of-way or easement shall be inspected and approved
by the Public Works Department. It is the Contractor's responsibility to notify the Public Works
Department of the work requiring inspection at least twenty-four (24) hours in advance so the Public
Works Department may schedule and perform such inspections.
GP-15 Guarantee for Equipment, Materials and Workmanship.
The Contractor shall guarantee all materials and equipment furnished, and construction work
performed for maintenance and repair work on existing public infrastructure for a period of one (1)
year from the date of written acceptance of the work by the City. The guarantee for new City
infrastructure shall be for a period of two (20 years from 'e date of written acceptance of the work by
the City.
GP-16 Stop Work Order.
A written Stop Work Order may be issued by the Public Works Department if the maintenance and
repair work in progress does not meet the Standards for Design and Construction for the City of
Kalispell, or for any other valid reason. Work may resume only after a written Resume Work Order
has been issued by the Public Works Department.
GP-17 Relocation of Utilities
Requests to relocate an existing public utility shall be submitted in writing to the Public Works
Department. A sketch shall be included that illustrates the existing location of the utility and the
preferred relocation site. The request shall describe in detail the circumstances for the request. The
Public Works Department may require the utility relocation to be designed by a licensed engineer. If
the relocation is approved by the Public Works Department the utility shall be relocated by a bonded
and insured utility contractor. Under no circumstances will the City of Kalispell pay for any costs
associated with the relocation of the utility.
6
CHAPTER II
DESIGN STANDARDS
DS-01 Design and Development Requirements.
The purpose of these standards is to establish the minimum requirements for the construction of
municipal facilities and improvements that impact municipal facilities.
Design Requirements. All water, sanitary sewer, storm drainage and roadway systems necessary to
provide service to and within a development shall be constructed at the Developer's expense and shall
be designed by a Professional Engineer licensed in the State of Montana. Plans, specifications and
design reports shall bear the seal of the Engineer in responsible charge of the design.
Water and sanitary sewer system designs shall be reviewed concurrently by the City Engineer and the
Montana Department of Environmental Quality, with approval of both required. Storm drainage and
roadway designs shall be submitted to and approved by the City Engineer. All required approvals
shall be obtained prior to beginning construction. Design calculations and testing results shall be
submitted to the City Engineer as required or requested.
Development Requirements. All subdivisions and developments shall be in compliance with The
Subdivision Regulations of the City of Kalispell, and these Standards for Design and Construction.
It shall be the responsibility of the Developer to construct all roadways and utilities from the existing
facilities to the far property line of the development or such other point within the development that
may be specified by the City Engineer. 11 utilities shall be within a public right-of-way or easement
to permit free and unobstructed acces
It is the Developer's responsibility to obta and provide the City with all easements and right-of-ways
necessary to extend roadways and utilities to the far property line of the development. The Developer
shall obtain written approval from the Kalispell Public Works Department stating they have reviewed
and approved the location of easements for the future extension of roadways and utilities which shall
be submitted with the final plat along with an I F by 17" legible copy of the approved final plat
showing the utility and/or easement locations.
There shall be reserved along the front lot line and side street lot line of each residential and
commercial lot a ten -foot (10') wide utility easement along, contiguous and adjacent to the lot line to
provide an area between the lot line and the easement line for the placement of privately owned
underground utilities.
All new utilities shall be placed underground. Underground private utilities shall be located between
the lot line and the easement line. No underground utilities, except service sweeps from the utility
trench to the street lights, utility boxes, pedestals, vaults, or transformers shall be placed in the
boulevard between the back of curb and sidewalk or within a sidewalk itself. No above ground utility
boxes, pedestals, vaults, or transformers shall be placed within any easement, proposed roadway, or
access way to any City facility.
Site plans, grading plans, and elevations used for infrastructure work shall be based on the North
7
American Vertical Datum 1988. Site plans, projects, designs, and surveys conducted on City property
or paid for with City funding shall be based on and utilize the local City horizontal coordinate system
(KAL 94). Assistance/coordinates can be obtained from the office of the City Surveyor.
DS-02 Water Systems
Water systems shall be designed, constructed, and tested in accordance with the current editions of
Montana Department of Environment Quality - Circular DEQ 1 -Standards for Water Works, The
Montana Public Works Standard Specifications and The Standards for Design and
Construction, Kalispell, Montana.
In addition, the following shall apply to the design of all Water Mains:
All water main extensions will require the Design Engineer to submit a written report to the City
Engineer which addresses the fire and domestic flow requirements. The report shall include flow test
results at the nearest hydrant to the development which shows the static pressure at zero flow from the
hydrant and the available flow from the hydrant at 20 psi residual pressure.
Valves shall not be located in gutter flowlines, sidewalks or street travleways.
The City will perform the required hydrant flow testing and will provide the test data to the Design
Engineer, at no cost, if so requested.
Isolation Valves. Isolation valves shall be installed at each lag, on each tee, and at each crossing of an
intersection. Distance between isolation valves shall not exceed 500 feet.
Fire Flow. Fire flow requirements sh be determined by the Kalispell Fire Department.
Minimum Pipe Sizes. The minimum than ter of all mains shall be eight inches (8"). Fire hydrant runs
less than fifty feet (50') in length may be permitted with six inch (6") diameter pipe.
Pipe Material. Water main piping from six (6) to twelve (12) inches in diameter shall be Class 150
PVC pipe conforming to AWWA C-900 Standards. All water main piping larger than twelve (12)
inches in diameter shall conform to AWWA C-905 Standards.
Water Service Lines. Structures containing two or more residences under separate ownership shall
have separate service lines, service valves and meters for each residence. Structures containing two or
more residences, offices, or businesses that are rental units under common ownership shall have one
service line, valve, and meter for all occupants within a single structure.
Gate Valves. Gate valves shall be Mueller Resilient Wedge Gate Valves, or an approved equal,
conforming to AWWA C-509 Standards.
Butterfly Valves. Butterfly valves shall be Mueller Lineseal Butterfly Valves, or an approved equal,
conforming to AWWA C-504 Standards. All valves over 12 inches in diameter shall be butterfly.
Fire Hydrants. Fire hydrants shall be Red Mueller Super Centurion Fire Hydrants with 5" Storz
adapter with cap conforming to AWWA C-502 Standards. The placement of all fire hydrants shall be
subject to the approval of the Fire Chief. Hydrant spacing shall not exceed; 500 feet along streets in
residential areas, 300 feet in commercial areas and 150 to 200 feet in industrial areas. Fire hydrants
shall be covered until placed in service.
Service Clamps. Service clamps for PVC water mains shall be H-13000 Series Mueller Brass, or an
approved equal, designed for use with AWWA C-900 PVC pipe.
Corporation Valves and Service Valves. Corporation valves and service valves shall be Mueller 300
Series ball valves, or an approved equal.
Service Fittings. Service fittings shall be Mueller Insta-Tite or 110 Series compression fittings, or an
approved equal.
Curb Boxes. Curb boxes shall be Mueller H-10308 or an approved equal, cast iron extension type with
arch pattern base, 1 1/2 inch I.D. upper section, minimum length 6 1/2 feet, equipped with a stationary
rod and a pentagon brass plug.
Service Pipe. Service pipe up to three (3) inches in diameter shall be polyethylene pipe conforming to
AWWA C-901 Standards. Service pipe four (4) inches or larger in diameter shall be Class 150 PVC
pipe, conforming to AWWA C-900 Standards.
Tapping Sleeves. Tapping sleeves shall be Romac SST III or an approved equal.
Ductile Iron Fittings. Ductile iron fittings shall be Class 350 SSB fittings conforming to AWWA
C-153 Standards.
Valve Boxes. Main line valve boxes all be igned for slip or screw type adjustment. Valve boxes
shall not be located in gutter flowlines r sid alks.
Mechanical Joint Restraints. Megalug, Mechanical Joint Restraints, or approved equal may be used at
all mechanical joint fittings. Thrust blocks shall be required at all mechanical joint fittings, whether
restrained joint fittings are used or not.
Warning Tape. Detectable warning tape shall be a minimum of 5 mils thick, three inches wide and
conform to APWA colors. Warning tape shall be buried twelve to 24 inches (12" — 24") below the
final ground surface.
Toner Wire. All mains shall be laid with 14 gauge insulated solid core copper toner wire. Toner wire
shall be insulated and taped to the top of the water main. Splices of toner wire shall be made with heat
shrink tape.
DS-03 Sanitary Sewer Systems.
Sanitary sewer systems shall be designed, constructed and tested in accordance with the current
editions of Montana Department of Environmental Quality - Circular 2 Design Standards for
Wastewater Facilities, Montana Public Works Standard Specifications and The Standards for Design
and Construction, Kalispell, Montana.
9
The following shall apply to the design of all sanitary sewers:
Minimum design contributing wastewater flows shall be: residential, 87 gpd/capita; commercial, 20
gpd/employee; and wet weather infiltration, 155 gallons per day per acre.
The City Engineer may require sulfide generation analysis. If dissolved sulfide is likely to exceed 0.2
mg/L, non -corrosive linings may be required in addition to special lift station design.
Watertight manhole covers shall be required in all locations where flooding may occur.
Valves and manhole covers shall not be located in gutter flowlines, sidewalks, or street travleways.
Gravity Sewers. Design Engineer shall submit a written report for all improvements or additions to
the sanitary sewer system. The report shall assess the ability of the existing collection system to
handle the peak design flow from the project and the impact on the Wastewater Treatment Plant.
Sewage Lift Station. A written report shall be submitted by the Design Engineer for any project that
requires a new sewage lift station or will contribute inflow to an existing sewage lift station. The
report for the new sewage lift station shall contain, but not be limited to, the following:
• A description of the proposed wet well, pumping system and force main.
• The capacity of the recommended pumps and potential for upgrading.
• A map showing the potential lift station service area.
• The average and peak design flows for the, roposed project and for the potential service
area.
• The hydraulic capacity of the force main.
• The reserve capacity of the lift station when t e proposed project is on line at full capacity.
• The pump run and cycle times for the average and peak design flows.
• Strategies for improvements which may be necessary to accommodate future sewer
extensions (i.e. increased storage, pumping or auxiliary power capacity).
• A statement of the pump selection process, including the Engineer's calculations for the total
dynamic head, total discharge head, net positive suction head and other pertinent pump
selection criteria.
• The designed pump operating curve plotted on a manufacturer's pump performance chart
with the designed operating point clearly identified.
The report for a project that will contribute inflow to an existing sewage lift station shall contain, but
not be limited to, the following:
• A description of the existing wet well, pumping system and force main.
• The capacity of the existing pumps and potential for upgrading.
• A map showing the potential lift station service area.
• A list of the existing users and their average design flows.
• The existing peak design flow and reserve capacity.
• The pump run and cycle times for the existing average and peak design flows.
• The hydraulic capacity of the force main.
• A list of the proposed users and their average design flows.
• The proposed average and peak design flows to the lift station.
• The reserve capacity of the lift station with the proposed project on line at full capacity.
10
• The pump run and cycle times for the proposed average and peak design flows.
• Recommendations for improvements, if necessary to enable the lift station to serve the
proposed project.
Unless otherwise approved by the City Engineer, new pumping systems shall be duplex, above ground,
self -priming, suction lift type and the pumps shall be equal to that manufactured by the Gorman Rupp
Company. The use of a proprietary name of a particular Supplier or Manufacturer is intended to
establish the type, function, and quality expected. Submersible 3" pumps or submersible grinder
pumps will be considered based on the required operating volumes and heads of the proposed lift
station.
An emergency natural gas fueled power supply shall be required for all lift stations. Noise emissions
from the power supply shall be limited to not more than 65 dbA at a distance of twenty (20) feet from
the power supply. One joint of ductile iron pipe, Class 50 cement lined, shall be installed on the
influent pipe to the wet well. The spigot end shall extend into the wet well 6" beyond the interior wall
of the wet well.
The lift station shall be served by an all weather 12-foot minimum width access way to provide access
by sewer maintenance vehicles. The access way at the s et shall have a concrete driveway paved
between the curb and the sidewalk.
Upon request from the City Engineer, the Design En ' eer shall submit a list of three lift stations of
the type proposed which have been in operatio ea five years. The City reserves the right to
accept or reject the proposed lift station.
An alarm system shall be provided that is capable of detecting power interruption, high water and high
motor temperature conditions. The alarm signals shall be directed to an on site alarm monitoring and
telephone dialer system. The alarm monitoring and telephone dialer system shall be an Antx, Inc.,
Dialog Elite, B-Channel auto dialer with modem (EMOD001) and pump cycle option (ECYC001). An
hour meter, suction pressure gauge tap and valve, and discharge pressure gauge tap and valve, are
required on each pump. Amperage meters are required on each leg of the electrical wiring. Controls
shall include a pump run alternator. The electrical power supply shall contain lightning protection.
The primary level control system shall be a transducer or air bubbler system. The backup level control
system shall be encapsulated mercury float switches.
All lift station facilities shall include a 6 ft. chain link security fence with a ten foot wide gate with two
five foot leaves.
Minimum Pipe Size. The minimum diameter of any gravity sanitary sewer main shall be eight (8)
inches.
Minimum Depth. The depths of sewers shall be in accordance with MDEQ Circular 2. (MDEQ
Circular 2, Paragraph 33.2 states, "In general, sewers should be sufficiently deep to receive wastewater
from basements and to prevent freezing. Insulation shall be provided for sewers that cannot be placed
at a depth sufficient to prevent freezing.").
Sanitary Sewer Service Lines. Structures containing two or more residences under separate
ownership, such as townhouses, shall have separate sewer service lines for each residence. Structures
containing two or more residences, offices or business that are rental units under common ownership
shall have one service line for all occupants within a single structure.
The terminal end of sanitary sewer services at undeveloped lots shall be marked in accordance with
MPWSS Standard Drawing No. 02730-2.
Quality of Sewage. No development shall introduce any sewage into the City of Kalispell Sanitary
Sewer System that is not consistent with the requirements of Ordinance 854, or as subsequently
amended. No storm water shall discharge to any sanitary sewer.
Sanitary Sewer Manhole Ring and Cover. The sanitary sewer manhole ring and cover shall be East
Jordan Iron Works Product No. NCR07-1738A, Olympic Foundry Part No. 11-3804, or approved
equal. The cover shall be marked SANITARY or SANITARY SEWER. Paint is at manufacturer
option.
Warning Tape for Force Mains. Detectable warning tape shall be a minimum of 5 mils thick, three
inches wide and conform to APWA colors. Warning tape shall be buried 12"-24" below finished
ground surface.
Toner Wire for Force Mains. All force mains shall be laid with 14 gauge insulated solid core copper
toner wire. Toner wire shall be insulated and taped to the top of the force main. Splices of toner wire
shall be made with heat shrink tape. All force mains burst through existing mains shall be installed
with'/4" steel toner cable.
Oil/Water Separators. Automotive repair facilities and paint shops, dealerships, gas stations,
equipment degreasing areas, and other facilities generating wastewater with oil and grease content are
required to pretreat these wastes before discharging to the City sanitary sewer system. Pretreatment
requires that an oil/water separator be installed and maintained on site.
Oil/water separators for commercial/industrial processes must be sized on a case -by -case analysis of
wastewater characteristics. Typically a minimum capacity of 750 gallons is required for small gas
stations, auto repairs, and light commercial sites; 1500 gallon capacity for large-scale truck washing
and steam cleaning facilities. The ultimate discharge must be directed to the sanitary sewer system.
All units regardless of size shall be fitted with a standard final -stage sample box and spill -absorbent
pillows.
Oil/water separators shall be commercially manufactured and sized for the intended discharge rates for
the facility where it is to be installed.
DS-04 Roadways and Walkways
Roadway systems including private roadways shall be designed, signed and constructed in accordance
with the current edition of the Standards for Design and Construction for the City of Kalispell,
Montana, the Montana Public Works Standard Specifications, the current Manual on Uniform Traffic
Control Devices, and The Subdivision Regulations of the City of Kalispell. All roads within a
proposed subdivision shall be designed by a professional engineer and approved by the City Engineer.
Upon completion of roadway construction, a professional engineer shall certify that the construction
12
meets the requirements of the Standards for Design and Construction, Kalispell, Montana.
Asphalt Surface. Pavement and material testing requirements shall be in accordance with MPWSS
Section 02510 Paragraph 3.29, except subsection E shall be replaced with: The field density and
thickness of the pavement is determined by measuring the cores tested. The actual thickness shall not
be less than the design thickness, and shall in no case be less than four (4) inches. And, subsection F
shall be replaced with: When the measurement of any core is less than the plan thickness, the actual
thickness of the pavement in this area may be determined by taking additional cores at intervals
parallel to the centerline in each direction from the affected location. Continue in each direction until a
core is found that is not less than the design thickness. The Engineer will evaluate areas found
deficient in thickness and determine which areas warrant removal. Remove and replace the areas with
asphaltic concrete of the thickness shown on the plans. Additional coring is considered as re -testing
of failing areas.
Traffic Analysis. Developments contributing three hundred (300) or more vehicle trips per day to the
City street system shall require a traffic impact analysis. A registered engineer with a Professional
Traffic Operation Engineer (PTOE) certification shall submit to the City a traffic impact analysis
report. This report shall state the existing traffic conditions for all impacted roadways, including the
existing levels of service for each road. The report shall identify all negative impacts associated with
the proposed development and shall thoroughly detail a mitigation plan for the negative impacts of the
proposed development. The developer shall be responsible to maintain the level of service of the
affected existing roadway system. The report shalt also take into consideration other forms of
transportation including bicycle and pedestrian.
The Traffic Impact Study shall be completed iriv accordance with Montana Department of
Transportation requirements and nationally acce t d standards. The Traffic Impact Study will assess
anticipated traffic impacts associated with theproposed development and recommend appropriate
mitigation measures for the adjacent trans o ation network.
Recommendations developed will be based upon nationally accepted traffic engineering principles,
related resources, and professional engineering judgment.
Cul-De-Sacs. All dead-end streets shall terminate in an approved cul-de-sac. Where future street
extension is proposed, a temporary cul-de-sac of adequate size as approved by the Fire Chief and City
Engineer shall be provided. Unless otherwise approved by the City Engineer, roadways that terminate
at a cul-de-sac shall have a maximum length of six hundred (600) feet. The cul-de-sac radius shall be
forty seven feet (47') to the back of the curb and fifty eight feet (58') to the right-of-way. A six foot
(6') boulevard and a five foot (5') sidewalk is required.
Horizontal Alignment. Horizontal alignment of streets must ensure adequate sight distances.
Collector street alignment shall be designed for a design speed of 35 miles per hour in accordance with
the latest edition of AASHTO A POLICY ON GEOMETRIC DESIGN OF HIGHWAYS AND
STREETS.
Collector and Arterial Streets. Location of collector and arterial streets shall comply with the
Kalispell Growth Policy or any other major street and highway plan adopted by the Flathead County
Board of County Commissioners and/or the City of Kalispell. The development of frontage roads or
shared accesses serving new developments shall be used along collectors and arterials rather than the
13
use of individual driveways or approaches.
Street Sub base. The sub base for streets shall be crushed stone in accordance with Montana Public
Works Standard Specifications Section 02234 and may include up to 3" minus material with at least
one fractured face. Larger material may be approved on a case by case basis, with at least one fractured
face.
Traffic Control Signs, Street Name Signs and Street Names. The Developer shall provide and install
the necessary Traffic Control Signs in accordance with the Manual on Uniform Traffic Control
Devices. Street name signs shall be installed at each intersection. All proposed street names shall be
submitted to the Public Works Department for approval prior to the preliminary plat submittal.
Sidewalks. All developments shall have sidewalks which will allow pedestrians to safely travel from
any part of the development to the boundaries of the development. Developments abutting existing or
proposed roadways will be required to have sidewalks within the public right-of-way and parallel to
the roadways. The minimum width of a sidewalk shall be five (5) feet. Sidewalks are required on both
sides of the street in all subdivisions. Sidewalks shall be separated from the street by a six foot wide
boulevard or open space that has been landscaped with in accordance with the Kalispell Street Tree
Ordinance and a plan approved by the Kalispell Parks and Recreation Department. No street trees shall
be located within fifty (50') feet of a street or stop sign.
Road Design Standards for,ocal Subdivision Streets
DESIGN STANDARDS ARTERIAU COLLECTOR LOCAL
Right -of -Way 80 ft. 60 ft. 60 ft.
Pavement Width
Maximum Grade
Cul-de-sac turnaround:
As approved by
City Engineer
Back of curb radius
8%
b. Minimum right-of-way radius
Maximum lengtl 2
34 ft.'
8%
28 ft.'
8%
47 ft.
58 ft.
600 ft.
On street parkinggoverned by City of Kalispell Subdivision Regulations.
2 Distance to be measured from the centerline of the intersection to the center point of the cul-de-sac.
14
Street Intersections. Street intersections shall meet the following requirements:
1. Streets shall intersect at 900 angles, if topography permits but in no case shall the angle of
intersection be less than 750 for a minimum distance of 60 feet as measured along the
centerline.
2. No more than two streets may intersect at one point.
3. Two streets meeting a third street from opposite sides shall meet the same point, or their
centerlines shall be offset at least 125 feet for local roads and 300 feet for collectors.
4. Intersections of local streets with major arterials shall be kept to a minimum.
5. Maximum straight tangent grade of approach to any intersection shall not exceed 2% for a
distance of 60 feet as measured from edge of transverse pavement to provide for adequate
starting, stopping and stacking distances.
6. The minimum back of the curb radii at street intersection shall be 20 feet.
7. Intersections shall be designed for a minimum sight distance of 150 feet. A minimum sight
distance of 200 feet shall be required in all vertical and horizontal curves.
DS-05 Driveways.
The nearest edge of any residential driveway shall be not less than thirty five (35) feet from the edge of
the pavement to the nearest intersecting street. All new driveway locations and modifications to
existing driveways shall be reviewed and approved by either the Building Department (Residential Site
Plan), the Site Development Review Committee (Development Submittals), or the Public Works
Department (Application for Driveway Construction) prior to beginning construction.
DS -06 Placement of Utilities.
Only water, sewer and storm sewers may, e placed within the street right-of-way. No underground
utilities, except service sweeps from the utility trench to the street lights, utility boxes, pedestals,
vaults, or transformers shall be placed in the boulevard between the back of curb and sidewalk or
within a sidewalk itself. No utility boxes, pedestals, vaults or transformers shall be placed within the
boulevard, any easement, proposed roadway, or access way to any City facility.
All applicable laws, rules and regulations of appropriate regulatory authority having jurisdiction over
utilities shall be observed.
DS-07 Street Lighting.
A. Purpose
1. Provide consistent and reliable lighting in outdoor public places where public health,
safety and welfare are concerns.
2. Provide lighting for vehicular traffic, pedestrian, and bicycle travel.
B. General
1. All new streets and subdivisions shall adhere to these standards.
15
2. All street lighting shall be designed to Flathead Electric Cooperative's (FEC) standards
(See Table 1), unless the light assemblies are owned and maintained by an entity other
than the City of Kalispell, (See Table 2).
3. All light fixtures shall be full cut off as defined in the Illuminating Engineering Society
of North America (IES).
4. All lighting layouts must be approved by the Public Works Department.
5. Light fixtures are required at at all intersections, mailbox groups, and pedestrian bus
stop locations.
C. Lighting
1. Intersections
a. All streets shall have lighting on at least one corner of the intersection. If the
street is four or more total lanes, two lights are required at diagonally opposite
corners, or sufficient fixtures to provide minimum foot candle levels.
2. Streets
a. Street lights shall be in accordance with the following tables and text.
Table 1-FEC's Standards
Classification
Fixture Type and pole
®
Lamp wattage
and Type
Spacing
Local
FEC's standard full cut-off cobra head w/Type
200W BPS
200 ft
Commercial
III distribution on a 30 foot pole, mounted to
FEC
Standard concrete pole bases.
Local
FEC's standard full cut-off cobra head w/Type
100W BPS
250 ft
Residential
III distribution on a 30 foot pole, mounted to
FEC
Standard concrete pole bases.
*Commercial as designated by the City of Kalispell.
b. All streets shall be illuminated from both sides of the street.
1. When streets contain less than four total lanes, lights on one side shall
be offset from the other side by the spacing criteria.
2. When streets have four or more total lanes, lights on one side shall be
offset from the other side by half the spacing criteria.
c. Light placement can vary from table spacing by a maximum of 15% with
approval from the Public Works Department.
d. If the road has sharp bends, lighting design must meet the average
illuminance and illuminance uniformity criteria established in Table 2.
e. For street lighting applications that do no conform to FEC's cobra head style
standards, i.e. Developer owned decorative fixtures in a subdivision; a
sidewalk photometric plan must be submitted with light placement that meets
the criteria shown in Table 2.
Table 2 — Owner metered/maintained
16
Classification
Average
Illuminance
Pole
Max lamp
Illuminance
Uniformity
Height
Wattage/type
(foot candles)
Ave/Min
Range
Local
0.6
6 to 1
20-30 ft
200W UPS
Commercial
Local
0.3
6 to 1
15-30 ft
100W BPS
Residential
'All values are to be measured on the sidewalk.
f Exceptions allowed if approved by the Public Works Department.
3. Pedestrian Gathering Areas
a. At all mailbox groups, bus stops, and pedestrian pathway intersections with
streets, a light fixture is required to indicate the location of this area.
D. Submittals
1. Street lighting plans shall be submitted to the Public Works Department for approval at
the same time as the street plans.
2. For all designs, submit design layout for p cement of light fixtures.
3. For designs following the criteria estab ' e ' Table 2, provide the following:
a. Photometric plan with isoil inanc ines indicating appropriate foot candle
levels.
b. On photometric plans, provide a table indicating average foot candles, ave/min
ratios, and max to min ratios for roadways, sidewalks, and pedestrian
intersections.
4. The Public Works Departmen has the authority to request photometeric plans if
deemed necessary to verify that these standards have been met.
DS-08 Utility Easements.
All public utility easements shall be fifteen (15) feet wide for a single pipeline, with the pipe centerline
five (5) feet from one easement edge. For easements with two pipelines, the minimum width shall be
twenty (20) feet with each pipe centerline five (5) feet from the easement edge.
DS-09 Multiple Use Paths
Non -motorized use paths shall be designed in accordance with the most recent version of AASHTO's
"Guide for the Development of Bicycle Facilities" and "Guide for the Planning, Design and Operation
of Pedestrian Facilities". Paths shall be a minimum of ten feet (10') wide. In limited instances, the
Public Works Director may require the path to be built to accommodate HS-20 loading if the path
serves as an emergency or maintenance access route.
No catch basins shall be located within the travel route of a path. Path signage shall conform to the
MUTCD. In subdivisions, required paths shall be located within common areas owned and maintained
by the property owners' association.
17
CHAPTER III
KALISPELL STORMWATER DESIGN MANUAL
SECTION1 LNTRODUCTION.......................................................................................................20
1.1 OBJECTIVE AND PURPOSE..................................................................................................20
1.2 USING THE STORMWATER MANUAL...............................................................................20
1.3 GENERAL REQUIREMENTS.................................................................................................20
1.4 STANDARD OF CARE............................................................................................................21
1.5 SEVERABILITY.......................................................................................................................21
SECTION 2 - BASIC REQUIREMENT1.........................................................................................22
2.1 INTRODUCTION.........................................................................................................................22
2.2 BASIC REQUIREMENTS........................................................................................................24
SECTION 3 - DRAINAGE SUBMITTA7P ........................................................................................29
3.1 INTRODUCTION.........................................................................................................................29
3.2 APPLICABILITY......................................................................................................................29
3.3 CONCEPT DRAINAGE REPORT.........................................................................................29
3.4 DRAINAGE REPORT..................................................................................................................30
3.5 ROAD AND DRAINAGE PLANS
............................................................................................33
3.6 OTHER SUBMITTAL ELEMENTS................................................................................34
SECTION 4 - GEOTECHNICAL SITE CHARACTERIZATION...................................................37
4.1 INTRODUCTION.....................................................................................................................
37
4.2 APPLICABILITY ......................................
37
4.3 GEOTECHNICAL SITE CHARACTERIZATION REPORT..................................................37
SECTION 5 - HYDROLOGIC ANALYSIS AND DESIGN............................................................42
5.1 INTRODUCTION.........................................................................................................................42
5.2 HYDROLOGIC ANALYSIS METHODS................................................................................42
5.3 CURVE NUMBER METHOD..................................................................................................42
5.4 LEVEL POOL ROUTING METHOD.......................................................................................51
5.5 RATIONAL METHOD.............................................................................................................52
SECTION 6 - WATER QUALITY TREATMENT DESIGN...........................................................55
6.1 INTRODUCTION.........................................................................................................................
55
6.2 WATER QUALITY PROTECTION STANDARDS...........................................................55
6.3 TREATMENT BMPS...............................................................................................................55
SECTION 7 - FLOW CONTROL......................................................................................................85
7.1 INTRODUCTION.........................................................................................................................
85
7.2 APPLICABILITY.........................................................................................................................85
7.3 DETENTION FACILITIES.........................................................................................................85
7.4 OUTFLOW CONTROL STRUCTURES..............................................................................88
7.5 INFILTRATION FACILITIES...................................................................................................95
7.6 RETENTION FACILITIES.........................................................................................................98
7.7 ADDITIONAL REQUIREMENTS FOR ALL FACILITIES...................................................98
7.8 SPECIAL REQUIREMENTS.....................................................................................................101
7.9 REGIONAL DETENTION PONDS...........................................................................................101
SECTION 8 -NATURAL AND CONSTRUCTED CONVEYANCE SYSTEMS .........................107
8.1 INTRODUCTION.......................................................................................................................107
8.2 APPLICABILITY....................................................................................................................107
18
8.3 NATURAL AND CONSTRUCTED CHANNELS....................................................................107
8.4 CULVERTS................................................................................................................................112
8.5 STORM DRAIN SYSTEMS...................................................................................................115
8.6 GUTTERS...............................................................................................................................117
8.7 DRAINAGE INLETS..............................................................................................................120
SECTION 9 - EROSION AND SEDIMENT CONTROL DESIGN...............................................127
9.1 INTRODUCTION....................................................................._................................................127
9.2 APPLICABILITY....................................................................................................................127
9.3 EROSION AND SEDIMENT CONTROL (ESC) PLAN...........................................................127
9.4 STORMWATER MANAGEMENT PERMIT............................................................................132
SECTION 10 - MAINTENANCE, PARCELS, AND EASEMENTS.............................................134
10.1 MAINTENANCE.....................................................................................................................134
10.2 PARCELS AND EASEMENTS...............................................................................................136
ABBREVIATIONS AND ACRONYMS.........................................................................................145
REFERENCES..................................................................................................................................146
19
SECTION 1 - INTRODUCTION
1.1 OBJECTIVE AND PURPOSE
Development projects in urban areas generally result in the replacement of open land with impervious surfaces that
prevent infiltration and increase stormwater runoff rate and volume. This changes the patterns of stormwater runoff,
which can lead to flooding problems —at the project site and on properties downstream —and can affect water
quality, as sediment and pollutants are transported into streams, wetlands, lakes and groundwater.
The purpose of Chapter III - Stormwater Design Manual, referred to as "manual" in this chapter of the Kalispell Standards
for Design and Construction, is to protect water quality, prevent adverse impacts from flooding, and control stormwater
nmoffto levels equivalent to pre -development.
1.2 USING THE STORMWA TER MANUAL
This manual provides engineers, developers, and the general public with procedures and assistance for designing
stormwater management facilities associated with land development, road and drainage projects. It outlines
minimum requirements for the design of stormwater management systems.
This manual references and refers information from the following City of Kalispell Documents:
• City of Kalispell 2008 Storm Water Facility Plan Update; and,
• City of Kalispell Stormwater Quality Management Plan.
1.3 GENERAL REQUIREMENTS
The owner or owner's agent is responsible for the following:
• Coordinating project consultants;
• Providing complete drainage submittals;
• Ensuring adherence to:
o The standards and criteria presented in this manual;
o The Conditions of Approval, if applicable;
o Any conditions establish by the City Engineer;
o General project management; and,
o Permits required by the City of Kalispell or other agencies.
The owner or owner's agent is required to obtain approval of the drainage submittal from the Public Works Department
prior to any of the following:
• Major and minor subdivision final plat approval;
• Site plan approval;
• Issuance of a Building Permit; and,
• Issuance of a City Excavation Permit (for work in City Right -of Way).
The drainage submittal shall be prepared in accordance with this manual. The submittal shall be prepared by a
professional engineer currently licensed in the State of Montana and shall be submitted to the Public Works Department
for review and acceptance.
The rate and volume of stormwater runoff originating on any proposed land development, road or area draining to,
across or through the project site shall be estimated in accordance with the criteria presented in this manual.
These estimates shall be the basis of the drainage report. The peak rate of stormwater runoff from any proposed land
development to any natural or constructed point of discharge downstream shall not exceed the pre -development peak
rate of runoff The post development volume of runoff can exceed the pre -development volume of runoff when the
required down -gradient analysis demonstrates that there will be no adverse impacts on down gradient properties or
existing natural and constructed conveyance systems.
20
Stormwater runoff from a developed site shall leave the site in the same manner and location as it did in the pre -
developed condition. Flow may not be concentrated onto down -gradient properties where sheet flow previously
existed. Drainage shall not be diverted and released downstream at points not receiving drainage prior to the proposed
development. A down -gradient analysis demonstrating that there will be no expected adverse impacts on down
gradient properties will be required.
1.4 STANDARD OF CARE
The standards presented in this manual should be considered the minimum requirements to be used in the design of
stormwater facilities. Due to special site conditions, environmental constraints, or other applicable laws,
stormwater management designs may frequently need to exceed the minimum requirements. It is incumbent upon the
engineer to use good engineering practice and to be aware of, and implement new design practices and procedures that reflect
current techniques in stormwater design, providing sufficient measures to ensure that the drainage facilities function
as intended. Good engineering practice is defined in these standards as professional and ethical conduct that meets the
current codes and regulations adopted for engineers. The proposed design shall consider functionality, constructability and
maintenance, including the health, safety and welfare of the public.
1.5 SEVERABILITY
If any section, sentence, clause or phrase of this manual should be held invalid or unconstitutional, the validity or
constitutionality thereof shall not affect the validity or constitutionality of any other section, sentence, clause or phrase of
this manual.
21
SECTION 2 - BASIC REQUIREMENTS
2.1 INTRODUCTION
This section introduces the seven Basic Requirements for new development and redevelopment projects in the City of
Kalispell:
• Basic Requirement No. 1 — Drainage Submittal;
• Basic Requirement No. 2 — Geotechnical Site Characterization;
• Basic Requirement No. 3 — Water Quality Treatment;
• Basic Requirement No. 4 — Flow Control;
• Basic Requirement No. 5 — Natural and Constructed Conveyance Systems;
• Basic Requirement No. 6 — Erosion and Sediment Control; and,
• Basic Requirement No. 7 — Operation and Maintenance.
The applicability of these requirements depends on the type, size, and location of the project. It is the responsibility of
the project owner or owner's agent to become familiar with the Basic Requirements in order to determine when they are
applicable.
2.1.1 REGULATORY THRESHOLD
The regulatory threshold is the "trigger" for requiring complianc with the Basic Requirements of this manual. In
the City of Kalispell, it is defined as "the addition or replacem t of 5000 square feet or more of impervious
surfaces at full development.
2.1.2 NEW DEVELOPMENT
New development is the conversion of previously undevel ermeable surfaces to impervious surfaces and
v managed landscape areas. New development occurs ac t land or through expansion of partially developed sites.
All new development projects, regardless of w ether the pT�ject meets the regulatory threshold, shall comply with the
following:
• Basic Requirement No. 3 — Water Qu reatment
• Basic Requirement No. 5 — Natural and Constructed Conveyance Systems; and,
Basic Requirement No. 6 — Erosion and Sediment Control.
All new development projects that meet the regulatory threshold shall comply with the following:
• Basic Requirement No. 1 — Drainage Submittal;
• Basic Requirement No. 2 — Geotechnical Site Characterization;
• Basic Requirement No. 3 — Water Quality Treatment;
• Basic Requirement No. 4 — Flow Control;
Basic Requirement No. 5 — Natural and Constructed Conveyance Systems;
Basic Requirement No. 6 — Erosion and Sediment Control; and,
Basic Requirement No. 7 — Operation and Maintenance.
The City Engineer reserves the right to require compliance with any or all of the Basic Requirements regardless of the
size of the project or the amount of impervious area added or replaced.
2.1.3 REDEVELOPMENT
Redevelopment is the replacement of impervious surfaces on a developed site. Redevelopment occurs when
existing facilities are demolished and rebuilt or substantially improved through reconstruction. Rebuilt or
reconstructed facilities are regarded in the same manner as new development and shall comply with the Basic
Requirements of this manual.
On redeveloped sites where pre-existing facilities remain, the old facilities are not subject to the requirements of this
manual if they remain hydraulically isolated from the new facilities. For projects that are implemented in incremental stages,
22
the redevelopment threshold applies to the total amount of impervious surface replaced at full build -out; the new
development thresholds apply to the total amount of new impervious surfaces added at full build -out.
The long-term goal of the redevelopment standard is to reduce stormwater pollution from existing developed sites,
especially when a water quality problem has been identified or the site is being improved to accommodate a use with a
greater potential to contribute pollution to the receiving waters.
A project may be granted a design deviation when site conditions prevent full compliance with the Basic
Requirements; however, every effort shall be made to find creative ways to meet the intent of the Basic Requirements.
Design deviations will not be granted waiving stormwater requirements for new impervious surfaces.
Sites with 100% existing building coverage that are currently connected to a municipally owned storm sewer or
discharge to water of the state must be evaluated on a case -by case basis to continue to be connected without
treatment; additional requirements such as flow restrictors may also be required.
2.1.4 EXEMPTIONS
Projects are exempt from the Basic Requirements when falling under any of the following categories:
• Actions by a public utility or any other governmental agency to remove or alleviate an emergency condition,
restore utility service, or reopen a public thoroughfare to traffic;
• Records of survey, boundary (i.e. minor lot line) adjustments, and property aggregations, unless the action
affects drainage tracts or easements;
• Projects that, when completed, will not have physically disturbed the land;
• Road and parking area preservation and maintenance project uch as:
o Pothole and square cut patching;
o Crack sealing;
o Shoulder grading;
o Vegetation maintenance; and,
o Operation and maintenance or re e ting facilities.
2.1.5 DESIGN DEVIATION
A design deviation is an administrative approval of design elements that do not conform to or are not explicitly
addressed by this manual.
The requirements of this manual represent the m' imum criteria for the design of stormwater management systems.
Designs that offer a superior alternative to standard measures, or creative means not yet specified in the standards, are
encouraged.
Applicability
The project owner or owner's agent shall request a design deviation when proposing non-standard methods, analysis,
design elements or materials. A design deviation will only be considered for review if:
• The design elements proposed do not conflict with or modify a condition of approval; and,
• The design elements proposed are based on sound engineering principles and best management practices,
and are not inconsistent with the public interest in stormwater control and environmental protection.
Submittal
For consideration of a design deviation, the project owner or owner's agent shall submit a design deviation request and
supporting documentation. The supporting documentation shall include sufficient information to make a decision as to
the adequacy of the proposed facility or design. If infiltration is proposed, negative impacts on down -gradient
properties are of concern, or seasonal high groundwater is suspected, then a geotechnical site characterization shall be
submitted as part of the design deviation package. The design deviation package shall demonstrate that:
• There are special physical circumstances or conditions affecting the property that may prohibit the application
of some of the Basic Requirements in this Manual;
• Every effort has been made to find alternative ways to meet the objectives of the Basic Requirements;
• Approving the design deviation will not cause adverse impact on down -gradient properties, public health or
welfare; and,
• Approving the design deviation will not adversely affect the recommendations of any applicable
23
comprehensive drainage plan.
2.2 BASIC REQUIREMENTS
2.2.1 BASIC REQUIREMENT NO. 1 - DRAINAGE SUBMITTAL
Projects are expected to demonstrate compliance with all applicable Basic Requirements through the
preparation of a Drainage Submittal. The Drainage Submittal shall include road and drainage construction plans, a
drainage report that describes the proposed measures to dispose of stormwater, and other supporting documentation
as needed. The contents of the Drainage Submittal will vary with the type, size, location of the project, and individual
site characteristics.
The City Public Works Department reviews the Drainage Submittal for compliance with this manual and other
applicable standards. Specific requirements for the Drainage Submittal are discussed in Section 3.
Applicability
The regulatory threshold or "trigger" for requiring compliance with this Basic Requirements is outlined in Section
2.1. A Drainage Submittal is generally required for any land -disturbing activity. Land -disturbing activities are those that
result in a change in the existing soil cover (both vegetative and non -vegetative) or site topography. The sections below
summarize the types of activities that require a Drainage Submittal, as well as those that are exempt.
A drainage submittal is required for the following types of activities:
• Commercial and industrial buildings including institutional and multi -family residential projects;
• Minor or major subdivisions;
• Change of use;
• Conditional use permits;
• Plan Unit Developments (PUD)
• Public or private parking lots; and,
• Public or private road projects.
The following types of activities are generally exepgtfFom the requirement to prepare a drainage submittal:
• Single-family residential/duplex building permits;
• Temporary use permits, unless the use couldcause adverse water quality impacts or other drainage -related
impacts;
• Land -disturbing activities that do not require a City Stormwater Management Permit for construction sites,
unless the activity could cause adverse water quality impacts or other drainage -related impacts;
• Maintenance projects that do not increase the traffic -carrying capacity of aroadway or parking area, such as:
o Removing and replacing a concrete or asphalt roadway to base course or subgrade or lower without
expanding or improving the impervious surfaces;
o Repairing a roadway base or subgrade;
o Resurfacing with in -kind material without expanding the area of coverage;
o Overlaying existing asphalt or concrete pavement with asphalt or concrete without expanding the area
of coverage; and,
o Chip seal projects.
The following types of activities are exempt from the requirement to prepare a drainage submittal:
• Actions by a public utility or any other governmental agency to remove or alleviate an emergency condition,
restore utility service, or reopen a public thoroughfare to traffic;
• Records of survey, boundary line adjustments, and property
aggregations, unless the action affects drainage tracts and easements;
• Operation and maintenance or repair of existing facilities; and,
• Road and parking area preservation/maintenance projects, such as:
o Pothole and square -cut patching;
o Crack sealing;
o Shoulder grading; or,
o Vegetation maintenance.
24
2.2.2 BASIC REQUIREMENT NO. 2 - GEOTECHNICAL SITE
CHARACTERIZATION
A geotechnical site characterization (GSC) is required to demonstrate suitability for stormwater disposal and to determine
sub -level structure construction feasibility. A professional engineer currently licensed in the State of Montana is
required to perform the GSC. Hydrogeologists and engineering geologists may prepare geotechnical site
characterization studies, excluding structural, foundation and pavement design. The study shall be performed in
accordance with the criteria specified in Section 4.
Applicability
The regulatory threshold or "trigger" for requiring compliance with this Basic Requirements is outlined in Section
2.1. A GSC will be required for most projects. The scope and geographic extent of the investigation may vary depending
on the general location and setting of the site, the characteristics of the target soil deposits, and whether there are known or
anticipated drainage problems in the vicinity of the site.
A GSC is required for:
• Projects proposing infiltration (infiltration facilities, detention facilities receiving credit for pond bottom
infiltration, etc.);
Projects located within or draining to a problem drainage area or study area as recognized by the City Engineer; or,
Projects with proposed sub -level structures (building foundations, City utilities, etc. or as required by the City
Engineer).
2.2.3 BASIC REQUIREMENT NO. 3 - WATER QUALITY TREATMENT
Water quality treatment is required to reduce pollutant loads and concentrations in stormwater. The BMPs described in
Section 6 are designed to reduce or eliminate certain pollutants. When required, treatment facilities shall be designed
according to the criteria specified below, in Section 6, and in the Stormwater Quality Management Plan.
Applicability
The regulatory threshold or "trigger" for requiring complianre with this Basic Requirements is outlined in Section
2.1. Water quality treatment is recommended but not required when the project is a part of a larger development which
already addresses water quality treatment. Th tormwater Quality Management Plan outlines specific requirement for
water quality treatment in the City of Kalis 1.
The project sites with water quality treatment ex ptions are superseded by requirements set forth in any applicable
Total Maximum Daily Load (TMDL) or other water cleanup plan. At the time of the writing of this manual, no TMDLs
exist for water bodies in the City of Kalispell. Contact the City Engineer for current information on whether any TMDLs
have been issued.
Design Criteria
1. Stream and River Flow Control Standard:
• Post development runoff rate shall be limited to no more than 50% of the pre -development 2-year, 24-hour peak
runoff rate (based on SCS Type 1 unit hydrograph); and,
• The post development 10-year peak runoff rate shall be no greater than the pre -development 10-year, 24-hour peak
runoff rate (based on SCS Type 1 unit hydrograph).
2. Wetland Standards
An on site wetland analysis is required for all new development. See Wetland Analysis in Section 3.4 Drainage
Report; and,
Flow control: See Wetland Flow Control Standards Chapter 6, in the Stormwater Quality Management Plan.
3. Water Quality Volume Standard
• The water quality volume for the design of BMPs is based on a snowmelt event. The design volume is the runoff
from 1.1 inches of equivalent snow pack moisture. Refer to the Stormwater Quality Management Plan and
Section 6 for more details.
25
2.2.4 BASIC REQUIREMENT NO. 4 - FLOW CONTROL
Flow control facilities are necessary to protect stream morphology and habitat and to mitigate potential adverse impacts on
down -gradient properties and floodplains due to the increase in stormwater runoff caused by land development.
The peak rate of stormwater runoff from any proposed land development to any natural or constructed point of
discharge downstream shall not exceed the pre -development peak rate of runoff. The post development volume of runoff
can exceed the pre -development volume of runoff when the required down -gradient analysis demonstrates that there will
be no adverse impacts on down gradient properties or existing natural and constructed conveyance systems. The City
Engineer reserves the right to deny a request for increased stormwater volumes or to condition any approval at their sole
discretion.
When site conditions allow, infiltration is the preferred method of flow control for urban runoff. All projects are
encouraged to infiltrate stormwater runoff on site to the greatest extent possible if such infiltration will not have adverse
impacts on down- gradient properties or improvements. Flow control facilities shall be designed and constructed
according to the criteria in Sections 5, 6, and 7.
Applicability
The regulatory threshold or "trigger" for requiring compliance with this Basic Requirements is outlined in Section
2.1. All projects that meet the regulatory threshold shall comply with this Basic Requirement.
Design Criteria
The NRCS Type I 24-hour storm event is the design storm for all flow control facilities that use a surface discharge
or a combined surface and subsurface system.
Infiltration Facilities: Infiltration facilities shall be sized to fully ' i e the post -development NRCS Type 1 10 year
24 hr design storm and the design water surface for all facilities still be 100 year post developed water surface
elevation. All overflows (structure or spillway) shall pass the 100 year -24 hr developed peak flow rate. The overflow
path shall drain toward the natural discharge point of the contributing basin, such that the overflow route or
termination of stormwater does not adversely impact down -gradient properties or structures.
Retention Facilities: For projects proposing Retention, th facilities shall be designed to store the 100-year 24 hr
post development storm events and shall prgvide an overflow path, wherever possible, with the capacity to convey the
100-year storm event.
Detention Facilities: For projects proposing to detain and release stormwater runoff, the facilities shall be designed
such that the release rate does not exceed the pre -developed conditions for a range of storm events. The analysis of
multiple design storms is needed to control and attenuate both low and high flow storm events.
The NRCS Type 124 hour storm events is the design storm to be used for all flow control facilities that use a surface
discharge. The design water surface for all facilities shall be the 100 year post developed water surface elevation. All
overflows (structure or spillway) shall be located above the design water surface elevation and pass the 100 year -24 hr
developed peak flow rate.
The total post -developed discharge rate leaving the site shall be limited to the pre -development rates listed in Table 2-
1. Bypass flow shall be discharge at the pre -developed flow rate. Bypass flow is the runoff that leaves the site without
being conveyed through the new development or redevelopment drainage system.
26
Table 2-1
Allowable Dischar a Rates
Design Frequency (24-hour storm)
Post -Developed Discharge Rate'
2-year
< 50 % of 2-year 24 hr pre -developed
10-year
<10-year 24 hr pre -developed
100-year2 (Emergency Overflow)
Overflow route only'
1 Post -developed flow is equal to the release from detention facility plus the bypass flow
2 The emergency overflow shall direct the 100-year post -developed flow safely toward the
downstream conveyance system
2.2.5 BASIC REQUIREMENT NO. 5 - NATURAL AND CONSTRUCTED
CONVEYANCE SYSTEMS
A conveyance system includes all natural or constructed components that collect stormwater runoff and convey it
away from structures in a manner that adequately drains sites and roadways, minimizing the potential for flooding and
erosion.
Engineered conveyance elements for proposed projects shall be an ed, designed, and constructed to provide
protection against damage to property and improvements from unc oiled or diverted flows, flooding and erosion
Projects shall be designed to protect certain natural drainage features including floodplains, natural drainage ways,
and natural depressions that store water or allow it to initrate into the ground. These features are collectively referred
to as the `Natural Drainage Ways" (NDW). Preserving the NDW will help ensure that stormwater runoff can continue to
be conveyed and disposed of at its natural location. Pr rvation also increases the opportunity to use the
predominant systems as regional stormwater fa ' ie . Refer to Section 8 and the 2008 Stormwater Facility Plan
Update for more information on NDW.
Stormwater runoff shall be discharged in the s e er and at the same location as in the pre -developed condition.
Stormwater runoff shall not be concentrated to down -gradient properties where sheet flow previously existed and
shall not be diverted to points not receiving stormwater runoff prior to development.
Applicability
All projects shall comply with this Basic Requirement regardless of whether they meet the regulatory threshold.
Design Criteria
Natural and Constructed Channels: Constructed and natural channels shall be designed with sufficient capacity to
convey, at a minimum, the depth associated with the 100-year design storm event peak flow rate, assuming developed
conditions for on -site tributary areas and existing conditions for any off- site tributary areas. Refer to Section 8 for
additional criteria.
Culverts under roadways or embankments: A culvert is a short pipe used to convey flow under a roadway or
embankment. Culverts are used to pass peak flow from defined drainage ways identified on contour maps. New culverts
shall be designed with sufficient capacity to convey the 100 - year design storm event assuming developed conditions
for the on -site basin and existing conditions for the off -site basin.
Gutters: Gutter flows in roadways shall allow for the passing of vehicular traffic during the 10-year design storm
event by providing non -flooded zones. For paved roadways, the non -flooded width requirement varies with the road
classification. The design shall meet the criteria specified in Section 8.
Storm Drain Systems and Inlets: The 10-year design storm shall be used to size the conveyance system regardless of the
method used to size the disposal facility.
27
Enclosed systems may surcharge or overtop drainage structures for storm events that exceed the drainage facility design
storm, as long as an overflow path is provided, wherever possible. The overflow path shall be capable of conveying
the 100-year storm event and should either drain toward the natural discharge point of the contributing basin
(preferred) or away from adjacent buildings, residences, etc. so as to avoid adverse impacts due to flooding.
2.2.6 BASIC REQUIREMENT NO. 6 - EROSION AND SEDIMENT
CONTROL
During the construction phase, sediment -laden runoff can enter newly constructed or existing drainage facilities, thus
reducing their infiltration or treatment capacity and their lifetime of operation, or increasing maintenance costs.
Controlling erosion and preventing sediment and other pollutants from leaving the project site during the construction
phase is achievable through implementation and selection of BMPs that are appropriate both to the site and to the season
during which construction takes place.
The objectives of the erosion and sediment control (ESC) Plan are to:
• Protect existing or proposed stonnwater management infrastructure;
• Minimize the impacts of erosion, sedimentation and increased runoff caused by land -disturbing activities on
private property, public roads and rights -of -way, and water bodies; and,
• Protect water quality.
Applicability
A City Stormwater Management Permit for construction sites is required for land -disturbing activities which include,
but are not limited to, excavation, planting, tilling, and grading, which disturbs the natural or improved vegetative
ground cover so as to expose soil to the erosive forces of rain, stonnwater runoff or wind. All installations and
maintenance of franchise utilities such as telephone, gas, electric, etc., shall be considered land disturbing activities.
The following land -disturbing activities require a City Stoftu*rb!Z�,tored,
M agement Permit:
• Any activity where the total volume of material ' disposed of or used as fill exceeds five (5)
cubic yards; or,
• Any activity where the area disturbed exceeds one ousand (1000) square feet provided it does not obstruct a
watercourse, and is not located in a floodplain.
low
A City Stormwater Management Permit for construction sites may not be required for all situations; however that
does not relieve the owner from the responsibility of controlling erosion and sediment during construction nor the
liability for damage claims associated with adverse impacts on off -site properties.
2.2.7 BASIC REQUIREMENT NO. 7 - OPERATION AND MAINTENANCE
To ensure that stormwater control facilities are adequately maintained and properly operated, documentation describing
the applicable preventive maintenance and recommended maintenance schedule shall be prepared and provided to
the entity responsible for maintaining the stonnwater system.
For stormwater control facilities outside of the public road right of way, the project owner shall provide the financial
means and arrangements for the perpetual maintenance of the drainage facilities. Owners shall operate and maintain the
facilities in accordance with an operation and maintenance plan that meets the criteria specified in Section 10.
Applicability
All projects that meet the regulatory threshold and that propose drainage facilities or structures shall comply with
this Basic Requirement. The regulatory threshold or "trigger" for requiring compliance with this Basic
Requirements is outlined in Section 2.1.
WE
SECTION 3 - DRAINAGE SUBMITTAL
3.1 INTRODUCTION
This Section describes the contents of a Drainage Submittal and provides a framework for preparing the submittal in order to
promote consistency. Specific best management practices (BMPs), design methods and standards to be used are contained in
Sections 4 through 10. Properly drafted construction engineering plans and supporting documents will help facilitate the
operation and maintenance of the proposed system long after its review and acceptance.
The Drainage Submittal is a comprehensive report containing all of the technical information and analysis
necessary for regulatory agencies to evaluate a proposed new development or redevelopment project for compliance with
stormwater regulations. Other supporting documentation shall be submitted as needed. Contents of the Drainage
Submittal will vary with the type and size of the project, individual site characteristics, and special requirements of
the City Engineer. The "trigger" for requiring compliance with this basic requirement is defined as "the addition
or replacement of 5000 square feet or more of impervious surfaces at full development.
3.2 APPLICABILITY
A Drainage Submittal is generally required for any land -disturbing activity. Section 2.2.1 summarizes the types of
activities that require a Drainage Submittal as well as those that are exempt.
3.3 CONCEPT DRAINAGE REPORrt
3.3.1 INTRODUCTION
Concept Drainage Reports are used by City staff to prelim' ss the drainage requirements on certain land -use
actions and land development permits. The purpose of the Concept Drainage Report is to demonstrate that the
proposed drainage facilities can meet the intent of this manual and are feasible with respect to design, construction, and
maintenance. Its contents are similar to those of the Drainage Report described in Section 3.4, though for many items
the Concept Drainage Report does not require as much detail as the Drainage Report.
IF
Preparation of a Concept Drainage Report is an initial step in the Drainage Submittal process, and acceptance of a
Concept Drainage Report does not imply that the concept proposed is accepted as the final design. A Concept
Drainage Submittal package is required at the pre -application stage and before preliminary plat approval.
Acceptance only implies that the project owner (or his agent) has demonstrated that stormwater disposal is feasible. It
does not relieve the project owner from a geotechnical site characterization, a down -gradient analysis, or changes to
the design that may be necessary in order to meet the criteria and standards presented in this manual.
3.3.2 APPLICABILITY
The need for a Concept Drainage Report varies depending upon the nature, scope, and complexity of the proposed project
and the existing drainage conditions. Due to the number of variables involved, this manual does not include an
exhaustive listing of all scenarios that may require a Concept Drainage Report. Concept Drainage Reports will be
required for any of the following situations, and the City Engineer has the authority to require a Concept Drainage Report
for any other project.
• The project lies within or is contiguous with an official 100-Year Flood Zone as mapped by the Federal
Emergency Management Agency (FEMA) (See Section );
• The project lies within or drains to an area identified as having drainage problems;
• The project lies within or drains to an area identified as having floodplains;
• The project is especially large, phased, or master -planned and may require interim facilities;
• The project site is greater than I acre;
• The project involves significant off -site drainage and relies upon a predominant drainage way;
29
The project site has features that can be classified as Natural Drainage Way (NDW) (refer to Section 8.3.4 for
definition); and,
The project has the potential to impact existing or future regional stormwater facilities.
3.3.3 SCOPE
The Concept Drainage Report shall demonstrate that the existing or proposed drainage infrastructure is
adequate to control the increase in runoff due to the proposed project by meeting the minimum requirements of this
manual.
A detailed design is not required at this stage because the exact nature of the proposal may not be certain. However, the
Concept Drainage Report shall provide sufficient information and analysis to demonstrate that adequate infrastructure
can be provided. Due to varying design parameters, design challenges, and potential solutions, the level of
requirements can change from site to site. For example, if an infiltration facility is proposed in an area known to
have shallow groundwater or bedrock, a geotechnical site characterization would be required at the Concept Drainage
Report stage to support the use of infiltration.
The Concept Drainage Report shall include the following elements:
• Narrative: The narrative shall generally follow Section 3.4.2 and shall describe all proposed methods and
alternatives for stormwater treatment and disposal, as well as provide sufficient information, supporting
technical data, assumptions, design criteria, and drainage calculations to demonstrate that the proposed
stormwater system will meet the requirements of this manual. If phasing is anticipated, an explanation of
how the drainage system will be phased and constructed sh also be included;
• Schematic: The schematic plan of the proposed stormwate stem shall show the approximate size and location
of all drainage components;
• Basin Map: The drainage basin maps shall generally fo w the requirements for maps presented in
Section 3.4.3;
a
• Geotechnical Information: If infiltration is proposed, then sufficient site characterization work shall be
completed in accordance with Section 4 to demonstrate that the proposed facilities will function as intended;
• Drainage Features: The report shall generally follow the requirements for pre -development basin information
presented in Section 3.4.2;
• Perpetual Maintenance of Facilities:,,The report shall generally follow the requirements for Perpetual Maintenance
of Facilities presented in Section 3.4.2, but may be less detailed;
• Offsite Easements: The report shall follow the requirements for off -site easements presented in Section 3.4.2;
and,
• Regional Facilities: The report shall follow the requirements for regional facilities presented in Section 3.4.2.
3.4 DRAINAGE REPORT
3.4.1 INTRODUCTION
The purpose of the Drainage Report is to identify drainage impacts resulting from land development activities and
determine the improvements necessary to control the increase in stormwater runoff and to treat the pollutants that can
adversely impact water quality.
A Drainage Submittal package is required with the engineers report as defined in the Construction and Design
Standards.
The Drainage Report shall be inclusive, clear, legible, and reproducible. An uninvolved third parry shall be able
to review the Drainage Submittal and determine whether all applicable standards in this manual have been met. The
basic elements of a Drainage Report are summarized in the following sections.
3.4.2 NARRATIVE
The drainage report narrative shall include the following elements:
• Project Description: The project description shall include information about the size of the project, the
30
number of lots proposed, the project location, and background information relevant to drainage design,
including topography, surface soils, surface and vegetative conditions, etc.;
• Geotechnical Information: This part of the narrative shall summarize the geotechnical site characterization
(GSC) for the project including recommended infiltration rates and on -site soil descriptions;
• Pre -Development Basin Information: This information shall summarize the pre -development drainage patterns
for all basins contributing flow to, on, through, and from the site. This section shall include all assumptions
and justifications used to determine curve numbers and/or runoff coefficients used in the analysis. The
narrative shall identify and discuss all existing on -site and/or off -site drainage facilities, natural or constructed,
including but not limited to NDW, conveyance systems, and any other special features on or near the project;
• Post -Development Basin Information: This information shall summarize all assumptions used to determine
the characteristics of the post -developed basins, such as the size of roofs and driveways, and the curve numbers
and/or runoff coefficients used in the analysis. In addition, a table shall be included that summarizes the
impervious and pervious areas for each subbasin;
• Wetland Anal A wetland analyses is required for all new development and redevelopment. A wetland
checklist, located in Appendix 3 A, is required to be completed and submitted with the drainage report. The
Wetland checklist helps to identify if wetland resources may be present and further wetland assessment is
required. If "yes" is checked for any wetland indicators on the checklist, a Wetland Assessment outlined in the
Kalispell Stormwater Quality Management Plan is required. The assessment must be performed by a wetland
professional trained and familiar with the current US Army Corps of Engineers Regional Supplements for
Wetland Delineations and the most recent Army Corps of Engineers guidance for Jurisdictional Determinations.
Refer to City of Kalispell Stormwater Quality Management Plan for additional details;
• Down -Gradient Anal This analysis shall identify and discuss the probable impacts down -gradient of the
project site;
• Methodology: The hydraulic methods and storm events use g the drainage facilities, including the BMPs
proposed for the project, shall be discussed;
• Water Quality Treatment: A discussion of treatment requi me s, based on the criteria in Section 6 and the
City of Kalispell Stomwater Quality Management Plan, shall be included;
• Results: The results of the calculations and a description o e proposed stormwater facilities shall be
included. When applicable, a table comparing the pre -developed and post -developed conditions
including rates and volumes shall also be included. A table shall be provided when applicable, summarizing the
maximum water elevation of the facilities for the
design storms, outflow structure information, the size of
facilities "required" by the calculations, and the size of the facilities "provided" in the proposed design;
• Operational Characteristics: Sufficient information shall be provided about the operation of the stormwater
system so that an uninvolved third party ,6an read the report and understand how the proposed system will
function under various conditions;
• Perpetual Maintenance of Facilities: A discussion shall be included of the provisions set forth to operate and
maintain the drainage facilities. The project owner's mechanism for funding the operation and maintenance for
stormwater facilities, including sinking fund calculations, shall be included (refer to Section 10 for more
information);
• Off -Site Easements: The anticipated location of any off -site easements shall be identified either on the basin
map or in a separate schematic. Off -site easements will be required for proposed stormwater conveyance or
disposal facilities outside the project boundaries. These easements shall be obtained and recorded prior to the
acceptance of the final Drainage Submittal (refer to Section 10 for more information); and,
• Regional Facilities: A discussion of any expected future impacts on or connections to existing or proposed
regional facilities shall be included (refer to Section 7.10).
3.4.3 FIGURES
Basin Map
The drainage report shall include a basin map. Both a pre -developed and post -developed basin map shall be provided.
The minimum elements required include the following:
• Vicinity map, project boundaries, and section, township, and range;
• Basin limits:
o Basin limits shall include on -site, off -site, and bypass areas contributing runoff to or
from the project.
• In all cases, the engineer shall field -verify the basin limits, including any contributing off -site areas, and
31
shall describe how the basin limits were determined;
• Drainage basins shall be clearly labeled and correlated with the calculations;
• Time of concentration routes, with each segment clearly labeled and correlated with the calculations;
• Labeled topographic contours:
o Contours shall extend beyond the project or drainage basin boundaries to the extent necessary
to confinn basin limits used in the calculations;
o For commercial projects, spot elevations may be acceptable in lieu of contours on post -
developed basin maps;
o Projects in an urban area shall use a maximum contour spacing of 1 foot; and,
o At the discretion of the City Engineer, projects outside an urban area, such as a large lot
subdivision, may use the best available topographic information, but not greater than 2
maximum contour spacing of 2 feet.
• Any drainage way including, but not limited to, NDW, constructed drainage features, wetlands, creeks,
streams, seasonal drainage ways, closed depressions, ditches, culverts, storm drain systems, and drywells;
• Floodplain limits, as defined by FEMA or other studies;
• Any geologically hazardous areas;
• Footprint of proposed drainage facilities such as ponds, infiltration facilities, pipes, NDW, and ditches;
• North arrow and scale;
• Existing and proposed easements, parcel land, open space, parkland; and,
• Adjacent streets.
Other Figures
• Site photos;
• Soils map;
• Any graphs, charts, nomographs, maps, or figures sed in th esign, when applicable; and,
• If infiltration is proposed, a geotechnical site characterization is typically required. As part of that study, a
geologic cross-section of the stormwater disposal area drawn to scale shall be included. The proposed
stonmwater disposal facilities shall be superim osed on the cross-section. All relevant geologic units shall be
clearly identified including the target di s layer and limiting layers.
3.4.4 CALCULATIONS
Calculations shall be presented in a logical format and provide sufficient information to allow an uninvolved third parry
to reproduce the results. All assumptions, input and output data, and variables listed in computer printouts and hand
calculations shall be clearly identified. Basins and design storm events shall be clearly identified on all calculations.
The Drainage Report shall incorporate all calculations used to determine the size of the facilities. Typical calculations
include, but are not limited to:
• Hydrologic/hydraulic calculations including pre- and post -developed peak rate and volume calculations, routing
calculations, design information for outflow structures, orifice information, a pond volume rating table or pond
volume calculations, etc.;
• Time of concentration calculations;
• Curve number (CN) or runoff coefficient (C);
• Water quality treatment calculations;
• Inlet capacity and bypass calculations;
• Detention/retention storage capacities;
• Calculations for ditches and natural drainage ways;
• Culvert and pipe calculations;
• Non -flooded width calculations for curbs and gutters; and,
• Energy dissipation calculations.
Refer to Sections 5 through 8 for additional information regarding the above calculations.
3.4.5 DOWN -GRADIENT ANALYSIS
The purpose of a Down -Gradient Analysis is to inventory natural and constructed down -gradient drainage features
and to identify and evaluate adverse down -gradient impacts that could result from the proposed project. Common adverse
32
impacts of land development include erosion, flooding, slope failures, changed runoff patterns and reduced
groundwater recharge (to springs, streams, wetlands and wells, etc.). Proposed drainage facilities are to be
designed to mitigate adverse impacts identified in the Down -Gradient Analysis.
A Down -Gradient Analysis is required for all projects. The level of detail required will vary depending on the location
and complexity of the project. At a minimum the analysis shall extend a quarter of a mile down gradient and may be
limited in scope by lack of access to adjacent properties.
This analysis shall include:
• A visual inspection of the site and down -gradient area by the engineer that extends to the location where adverse
impacts are anticipated to be negligible;
• A site map that clearly identifies the project boundaries, study area boundaries, down -gradient flow path,
and any existing or potential areas that have been identified as problematic;
• A written summary addressing the following items:
o Existing or potential off -site drainage problems that may be aggravated by the
project;
o The condition and capacity of the conveyance route including all existing and proposed
elements, potential backwater conditions on open channels, constrictions or low capacity
zones, surcharging of enclosed systems, or localized flooding;
o The presence of existing natural or constructed land features that are dependent upon pre -
developed surface or subsurface drainage patterns;
o Potential changes to groundwater characteristics that may negatively impact sub -level
structures, foundations, or surface areas due increased amount or increased frequency or
duration of groundwater intrusion;
o Existing or potential erosive conditi s such as scour or unstable slopes on -site or down -
gradient of the project; and,
o Flood areas identified on FEMA aps.
• If there are existing or potential off -site drainage pr blem wn-gradient of the project, it shall be
demonstrated that the proposed stormwater isposal syste has been designed to meet all of the following
conditions:
o The stormwater rnno ves the site in the same manner as that of the pre -developed
condition;
o Reduced or increased groundwater recharge has been considered with respect to potential
adverse impacts on down gradient features; and
o The proposed design does not aggravate an existing drainage problem or create a new drainage
problem.
• If down -gradient surface release is at a rate or volume greater than the pre -developed condition is proposed, then
the following item shall also be addressed in detail:
o Potential adverse impacts on natural or constructed drainage channels due to an increase in
stormwater rate, volume, velocity, and flow duration.
3.5 ROAD AND DRAINAGE PLANS
3.5.1 INTRODUCTION
Construction drawings shall be submitted for review by the City Engineer. The submittal and acceptance process shall
be in accordance with the City standards and specifications. All plan sheets for every submittal shall be signed and dated
by the project owner, or his authorized agent, and all plan sheets shall be stamped and signed by the project engineer.
Once the Drainage Submittal has been accepted by the Public Works Department, a set of road and drainage plans
shall be submitted to Public Works on good quality media, stamped by the project engineer, labeled construction
plans, and dated.
33
3.5.2 MINIMUM PLAN ELEMENTS
The road and drainage plans shall provide enough detail for a third party to construct the proposed facilities per the
engineer's design. At a minimum, the plans shall meet the criteria of the City standards and specifications, and provide
the following information:
• Flow line and/or spot elevations, slopes, lengths, and cross -sections of ditches;
• Rim elevations of inlet grates, drywells, and other structures;
• A rp ofile of the stormwater conveyance system including pipes, culverts, ditches and connections, where
applicable. The profile shall include the sizes, material types, lengths, slopes, and invert elevations of all
conveyance elements;
• The minimum depth from finish grade to pipe invert and the minimum pipe slope necessary to satisfy the
freeboard and self-cleaning velocity requirements shall be provided;
• Where drainage infrastructure such as roadside swales or parallel conveyance ditches or channels may
interfere with driveway locations, driveway locations shall be fixed as part of the road and drainage plans
and shown on the plans;
• Record drawing information, including invert elevations of any existing drainage system elements that will be
used in the new design;
• Construction details drawn to scale or a referenced standard drawing for all structures;
• Drainage easements with all survey information shown and a recording number if applicable;
• Grading plan for drainage facilities and swales. The grading plan shall include existing and proposed contours
and catch points. A cross- section of each pond or Swale shall be provided in the plans, showing bottom
elevation, drainage structure elevation, maximum water surface elevation for the design storm(s), inlet and
outlet elevations, berm elevation and slopes, landscaping andgetation requirements, compaction requirements
and keyway location and dimensions;
• Each drainage pond/swale corner, pipe inlet or outlet, pipe sys angle point, ditch, and drainage structure,
shall be horizontally defined with respect to property corners, s eet stationing, or a coordinate system; and,
• Material gradation, thickness, and dimensions of riprap pads
3.5.3 REVISIONS AFTER PLAN AC E TANCE
When changes to the design are necessary, acceptance of any proposed plan changes shall be obtained in writing from
the City Engineer. The proposed revisions shall be stamped and signed by an engineer and submitted to the Public
Works Department for review and acceptance prior to construction. The submittal shall include:
• A brief description of the proposed changes and the purpose for the change;
• Substitute pages of the originally accepted construction plans that include the proposed changes; and,
• Calculations and supporting documentation for the proposed change demonstrating that the proposed
modified design is at least equivalent to the originally accepted design.
3.6 OTHER SUBMITTAL ELEMENTS
As determined by the City Engineer, the following items shall be included as part of the Drainage Submittal:
• A geotechnical site characterization, which may also include a sub -level structure feasibility analysis,
pavement analysis, pavement subgrade sampling, down -gradient analysis, etc;
• An erosion and sediment control plan;
• A draft copy of the Conditions, Covenants and Restrictions (CC&Rs) for the homeowners' association in charge
of operating and maintaining the drainage facilities (refer to Section 10);
• An operations and maintenance manual (refer to Section 10);
• A financial plan (refer to Section 10); and,
• On -site and/or off -site easement documentation (refer to Section 10).
34
Appendix 3A
Checklist for Identifying Wetlands
Site Data
Subdivision/Parcel
Completed by:
Evaluation date: Site visit date:
Location: Township Range Section (... ...
)
Physical Address:
Wetland Checklist: Pre Site Visit Survey
The following questions should be answered prior to a site visit using publicly available tools. If the
response to any of these questions is yes, it is possible that a wetland is present on the parcel and
the Site Visit Survey portion of this checklist should be completed. If no "Yes" answers, wetlands may
still be present and wetlands should still be considered during the site visit.
Yes No
❑ ❑ 1. Does the parcel or any adjacent parcels include U.S. Fish and Wildlife
Service National Wetland Inventory (NWI) mapped wetlands? Referto U.S. Fish
and Wildlife Service National Wetlands Inventory maps (http://www.fws.gov/nwi�.
1101
2. Does an aen to of the parcel or any adjacent parcels show surface
El Elwater? Refer to c rent aerial photo of property and other maps including U.S.
Geological Survey topographic maps and digital hydrography layers
(h ttp://n h d. usgs. go u/).
❑ ❑ 3. Is the parcel or any adjacent parcels located within the 100-year floodplain?
Refer to current floodplain maps available through County floodplain administrators.
4. Are there any streams, canals, ditches, or drainages present on the parcel
❑ ❑ or any adjacent parcels? Refer to current aerial photo of property and other maps
including U.S. Geological Survey topographic maps and digital hydrography layers
(h ttp://n h d. usgs. go .
5. Does the parcel or any adjacent parcels have hydric soils mapped? Refer to
❑ ❑ the most current soil survey data available through the Natural Resources Conservation
Service (http://soils.usda.gouy.
❑ ❑ 6. Is there documentation of shallow groundwater on the parcel, or any adjacent
parcel? Refer to groundwater data sets available from County Environmental Health
Departments.
35
Wetland Checklist: Site Visit Survey
Wetland Indicators
The following questions are for use during a site visit and will help determine if a wetland may be
present at the parcel and if it is likely to be regulated by federal, state or local laws or regulations. If
you check `yes" for any wetland indicators below, a Wetland Assessment outlined in the Kalispell
Stormwater Quality Management Plan is required. The assessment must be performed by a
wetland expert.
Yes No Wetland Hydrology
❑ ❑ 7. Is standing or flowing water observed at the parcel during the growing season?
❑ ❑ 8. Is the soil waterlogged during the growing season?
❑ ❑ 9. Are there water marks on any trees, shrubs, fencelines, buildings, etc.?
❑ ❑ 10. Optional (if you have had wetland delineation training) are there any primary or
secondary hydrology indicators present?
Wetland Vegetation
❑ ❑ 11. Does the parcel have plant communities that commonly occur in areas having
standing water for part of the growing season (e.g. cattail marshes, sedges,
bulrush, willows)?
❑ ❑ 12. Are any of the plants shown in the guide to `Common Wetland Plants of
Western Montana' present?
❑ ❑ 13. If the parcel has been cleared of vegetation or mowed, are there adjacent
areas that have plant communities or wetland plants connected to the parcel?
Wetland Soils
❑ ❑ 14. Does soil show any hydric indicators (consists of predominantly decomposed
plant materials, thick layer of decomposing plant material on the surface, sulfur
odor, or soil is bluish gray)?
❑ ❑ 15. Is there standing water or is the soil surface either saturated or inundated?
❑ ❑ 16. Are the soils wet at or near the surface during dry summer periods?
0
SECTION 4 - GEOTECHNICAL SIM
CHARACTERIZATION
4.1 INTRODUCTION
This Section outlines the minimum requirements for a geotechnical site characterization (GSC), which is used in
developing recommendations for stormwater disposal and determining the feasibility of constructing sub -level
structures. A professional engineer currently licensed in the State of Montana is required to perform the GSC.
Hydrogeologists and engineering geologists may prepare geotechnical site characterization studies, excluding
structural, foundation and pavement design.
The following geotechnical studies, if required, can be performed at the same time as the GSC:
• Geohazard analysis;
• Pavement subgrade evaluation;
• Down -gradient analysis;
• Embankment recommendations for proposed disposal facilities that would impound stormwater; and
• Recommendations for all cut and fill slopes.
Contact the City Engineer for specific requirements with regard to geohazardous areas and road surfacing. The
requirements of this Section are in addition to any field or laboratory testing that may be required, or recommended
by the project engineer, with regard to footings, foundations, ut�lity wor1V
c.
In known drainage problem areas, the geotechnical engineer may make recommendations on the feasibility of sub -level
structures based on the information available from the initial site instigation.
4.2 APPLICABILITY -40wr
A GSC will be required for most projects he regulatory threshold or "trigger" for requiring compliance with
this Basic Requirements is outlined in Secti n 2.1. The scope and geographic extent of the investigation may vary
depending on the general location and setting of the site, the characteristics of the target soil layer, and whether
there are known or anticipated drainage problems in the vicinity of the site.
A GSC is required for:
• Projects proposing infiltration (infiltration facilities, detention facilities receiving credit for pond bottom
infiltration, etc.), drywells, or non-standard drainage systems;
• Projects located within or draining to a drainage problem or study area as recognized by the City Engineer; or,
• Projects with proposed sub -level structures, i.e. footings, foundations, and utility work.
4.3 GEOTECHNICAL SITE CHARACTERIZATION REPORT
The following are minimum requirements for the GSC:
• The Study shall include:
o A surface reconnaissance of the site and adjacent properties to assess potential impacts
from the proposed stormwater system and to verify that the conditions are consistent with the
mapped information. Typically, the evaluation should extend a quarter of a mile down gradient.
Where access to adjacent properties is unavailable, the project owner shall rely upon the best
known information for the area, supplemented with information available from the City Engineer,
including any existing geotechnical engineering reports or studies for sites in the vicinity;
o A review of available geologic, topographic, and soils, and identify any site conditions that
could impact the use of storm drainage systems or the construction of sub -level structures. This
review shall include all available previous geotechnical engineering reports or studies for sites
in the vicinity; and,
o An evaluation of the potential impacts of groundwater on the proposed storm drainage
37
facilities, roadways and proposed underground structures, when a seasonally high
groundwater table is suspected.
• The Report Narrative shall include:
o A brief project description including size, number of lots proposed, project location (section,
township and range), and background information relevant for drainage design;
o A discussion of the study investigations;
o A description of the soil units on the site and in the vicinity of the site;
o A description of the site including surface, soil, and groundwater conditions, etc; and,
o Conclusions and recommendations.
• The Site Plan shall include:
o Project boundaries (including all existing and proposed property lines);
o Labeled topographic contours, extending beyond the project and drainage basin. Projects in an
urban area shall use a maximum contour spacing of 1 foot;
o Location of the soil units identified;
o Location of significant structures, properties or geologic features on site and in the project
vicinity;
o Location of existing natural or constructed drainage features on site and in the project vicinity;
and,
o Location of proposed site infrastructure including roadways and drainage features such as ponds,
drywells, etc.
• Test Method Documentation shall include:
o A map with the location of all subsurface field explorations and any in- place field tests;
o A description of any difficulties encountered during excavation and testing;
o A description of the equipment used to perform the field explorations or tests. When
applicable, describe the type of fabric lining and gravel backfill used;
o Logs of subsurface explorations which shall identify the depth to groundwater, the
presence of any limiting layers and the target soil layer; include test pit or excavation
dimensions, with photographs, where applicable;
o Report test data in a format that includes time of day, flow meter readings, incremental flow rates,
observed head levels, water depths and total flow volumes in the test pit or infiltrometer; and,
o A description of the condition of any existing facilities being tested, noting any silt build-up,
water level, connections to other structures (including distance to inverts of any interconnecting
pipes), measured depths and imensions, etc.
• Results of field and laboratory testing co cted, including the grain size analysis represented both
graphically and in tabular format
• A report on the actual and proposed design outflow rates for test pits;
• Results of the sub -level structure feasibility study and a summary of the down -gradient analysis as applicable;
and,
• A geologic cross-section of the stormwater disposal area drawn to scale, with the proposed stormwater
disposal facilities superimposed on the cross-section. All relevant geologic units shall be clearly
identified including the target disposal layer and limiting layers.
4.3.1 FIELD AND LABORATORY TESTING
The subsurface exploration, testing, and associated engineering evaluations are necessary to identify permeable
soils and to determine the thickness, extent, and variability of the soils. This information is necessary to properly design
stormwater disposal facilities.
Field explorations and laboratory testing shall be conducted under the direct supervision of a civil engineer, a
geotechnical engineer, a hydrogeologist , or an engineering geologist.
Test Methods
Soil infiltration rates shall be determined using one or more of the following methods for new development or
redevelopment with greater than or equal to 10,000 square feet of new impervious surface:
• The ASTM D 3385-88 Double -ring Infiltrometer Test: This test method is used for field measurement of
infiltration rate of soils;
• EPA Falling Head Percolation Test Procedure (Design Manual On -site Wastewater Treatment and Disposal
W:1
System, EPA, 1980;
• The Pilot Infiltration Test Procedure: This test method uses field data to estimate the outflow rates of subsurface
disposal facilities (refer to Stormwater Quality Management Plan: Pilot Infiltration Test Procedure Appendix C);
• Additional or alternate test methods, upon approval from the City Engineer.
For new development or redevelopment with less than 10,000 square feet of new impervious surface the soil infiltration
rates rate shall be determined by one of the above methods or:
• Montana Department of Environmental Quality (DEQ) Circular 4 Percolation Test.
Minimum Requirements
The following minimum requirements, when applicable, shall be met for field explorations and laboratory
testing when subsurface disposal is proposed:
• Test borings and/or test pits shall be located within the footprint of proposed stormwater disposal facilities; and,
• For each facility, a minimum of one subsurface exploration shall be performed for up to 1200 square feet of
disposal area. Another subsurface exploration shall be performed for each additional 15,000 square feet, or
fraction thereof, of disposal area. For a linear roadside swale, a minimum of one subsurface exploration shall be
performed every 500 feet, staggered on both sides of the road, unless site conditions or test results
indicate that additional explorations are necessary. Subsurface explorations and sampling shall be conducted
according to applicable standards of the American Society for Testing and Materials (ASTM).
Post -Construction Testing
Newly constructed infiltration facility will require a full-scale successful test prior to project engineer certification.
Refer to Appendix 4A for flood test methods. Contact the City Eng' i1�
r for additional information.
4.3.2 SUB -LEVEL STRUCTURE FEASIBI
If sub -level structure construction is being considered, a sub -level structure feasibility study is required. Field
explorations and laboratory testing shall be conducted under the direct supervision of a geotechnical engineer,
hydrogeologists, or an engineering geologist. Test boring shall be performed per the geotechnical engineer, a
hydrogeologist, or an engineering geologist recommendation or at minimum of one per 10,000 square feet.
Ground water shall be monitored during seasonal high grJund water conditions. The sub -level structure
feasibility study shall include the following, at a minimum:
• A layout of the site showing lot lines and lot and block numbers;
• Identification by lot and block number of sites where sub -level structure construction is feasible. Provide
recommendations with details of construction (i.e. maximum below grade floor elevations, minimum drainage
system requirements, and any site specific recommendations);
• Discussion of the effects of hydrostatic pressure that may lead to basement flooding and recommendations as
to the effectiveness of waterproofing;
• If infiltration is proposed as a method for stormwater disposal, discussion of any potential adverse
impacts on proposed sub -level structures, taking into consideration the contribution of imported water (due to
lawn watering, etc.); and,
• Identification of locations where sub -level structure construction is not feasible. When field and research data
indicate season high ground water is 1) below 15 feet, basements and crawl spaces would be allowed, 2)
between 5 feet to 15 feet, basement construction would be prohibited, 3) at 5 feet or less, both basement
and crawl space would be prohibited.
Language regarding sub -level structure restrictions shall be placed or referenced on the face of the plat. If a potential
buyer would like to construct a sub -level structure in an area deemed not feasible, then a site specific geotechnical
evaluation shall be performed by a geotechnical engineer for the individual lot prior to a building permit being issued.
Recommendations shall be summarized and provided electronically in Microsoft Excel, per the format found in
Table 4-1.
M1
Table 4-1
Example Sub -level Structure Feasibility Summary
Summary of Geotechnical Recommendations3
Block
Lots
yes
Maximum
C= 15 feet
Based upon the clean nature of the soils at the sub-
1
1-8
allowable
GrW=25 feet
level elevations and the depth to groundwater,
P
footing drains are not required. However, below-
B=30 feet
grade walls shall be well reinforced to reducing
cracking and thoroughly damp -proofed with a water-
resistant bituminous emulsion or modified cement
base coating. Backfill material shall consist of only
clean granular material which is free of fine-grained
soils, organic material, debris and large rocks.
Block
Lots
yes
4 feet
GrW=13 feet
Below -grade walls shall be well reinforced to reduce
2
1-3
cracking and waterproofed with a membrane (per
IRC) which is lapped and sealed from the top of the
footing to the finished grade. An under slab
waterproof membrane (per IBC) which is lapped and
sealed shall be integrated with the wall membrane.
Backfill material shall consist of only clean granular
material which is free of fine-grained soils, organic
material, debris and large rocks. Walls and footings
all have a drain system with cleanouts, emptying a
nimum of 15 feet in a down -slope direction away
1<drain
from structures. Precautions shall betaken not to
excavate a closed depression over rock or clay that is
intended to dispose of sump water from a foundation
system.
Block
Lots
no
n/a
GrW=6 feet
Due to the very shallow presence of groundwater,
2
4-8
B=10 feet
sub -level structures are not recommended on these
lots. If a crawl space is proposed, a drain system with
cleanouts shall be provided that empties a minimum
of 15 feet in a down -slope direction away from
structures. Precautions shall be taken not to excavate
a closed depression over rock or clay that is intended
to dispose of sump water from foundation drain
system.
1 Maximum depth measured from original pre-construction/pre-grading ground surface elevation or existing ground
surface, whichever provides a greater distance between the lowest floor elevation and the limiting layer.
2 GrW=groundwater, B=bedrock or basalt, C=clayey-silty soils
3 Refer to the Geotechnical Report for this project for further information, which may include construction
details that support these recommendations.
40
APPENDIX 4A
SWALE FLOOD TEST
Purpose
The swale flood test verifies the path of flow into a swale and the drawdown time of a bio-infiltration swale. The flood
test shall be conducted, when required, after the swale has been constructed and the vegetation has been established
(i.e. is not in danger of being washed out when water is introduced into the swale).
Procedure
1. Introduce clean water into the swale by directing the water (via hose from a hydrant or other clean water
source) along the curb and gutter upstream of the Swale inlet.
2. Raise the water level in the Swale until it reaches 6 inches in depth (typically to the rim of the drywell or catch
basin). Discontinue flow and note the time; this is the beginning of the flood test.
3. If the Swale is draining rapidly, the progress is observed, and when the Swale is empty, the time is
documented, and the flood test has ended.
4. If the Swale is not draining, measure the depth of water currently in the Swale, documenting the time, and
return to the swale site at a later time in order to verify that the swale has completely drained within 72 hours.
POND FLOOD TEST
Purpose
The Pond Flood Test Method verifies drawdown time o tormwater disposal facility, such as a detention
pond. The pond flood test shall be conducted, when required, er the pond has been constructed, and after
vegetation has been established (Le. is not in d er of being washed out when water is introduced into the
pond).
Procedure
1. Introduce clean water into the p se some form of splash -guard or diffuser device to prevent
surface erosion of the pond.
2. Raise the water level in the pond until it reaches operational depth (i.e. to the invert elevation of the first
outlet device (culvert, orifice, weir, etc.). Discontinue flow.
3. Document the time and measure the depth of water in the pond; this is the beginning of the pond flood
test.
4. The pond's ability to drain is observed. If the pond appears to be emptying rapidly, as soon as the pond is
empty, the time is documented, and the flood test has ended.
5. If the pond is not draining, or is draining very slowly, measure the depth of water currently in the pond,
documenting the time, and return to the pond site at a later time in order to verify that the pond has
completely drained within 72 hours.
NOTE: Contact the City Engineer for specific requirements for this Test Method. Some ponds will be large
enough that a pond flood test may not be the most efficient method of determining drawdown time or
infiltrative ability. Consideration may need to be given to other types of infiltrative test methods, such as the
double -ring infiltrometer test.
41
SECTION 5 - HYDROLOGIC ANALYSIS AND
DESIGN
5.1 INTRODUCTION
This Section provides the tools for estimating peak flow rates and volumes for sizing conveyance, treatment, and flow
control facilities. Standard flow control facilities are detention, retention and infiltration facilities. Flow control facilities
are necessary to mitigate potential adverse impacts on down -gradient properties due to the increase in stormwater runoff
caused by land development.
The peak rate of stormwater runoff from any proposed land development to any natural or constructed point of discharge
downstream shall not exceed the pre -development peak rate of runoff The post development volume of runoff can exceed
the pre -development volume of runoff when the required down -gradient analysis demonstrates that there will be no adverse
impacts on down gradient properties or existing natural and constructed conveyance systems.
Stormwater runoff from a developed site shall leave the site in the same manner and location as in the pre -developed
condition. Flow may not be concentrated onto down- gradient properties where sheet flow previously existed. Drainage
shall not be diverted from a proposed development and released downstream at points not receiving stormwater
runoff prior to the proposed development.
5.2 HYDROLOGIC ANALYSIS METHODS
The following methods shall be used for the design of flow con facilities and conveyance systems:
• The most commonly used Curve Number Metho e Mral Resources Conservation Service Urban
Hydrograph Method (MRCS Method). The atura e rce Conservation Service (MRCS) Curve Number
(CN) Method can be used to calculate:
o Peak flow rates;
o Flow control vol s; and, loe
o Water quality volum (WQv) (see Stormwater Quality Management Plan).
• The Level Pool Routing Method can be used to route hydrographs; and,
• The Rational Method can be used to estimate peak runoff rates.
5.3 CURVE NUMBER METHOD
5.3.1 INTRODUCTION
Single -event hydrograph methods based on the curve number equation can be used in combination with a routing technique to
size stormwater facilities. These methods are used to develop hydrographs to estimate the peak flow rate and volumes for a
specific design storm.
5.3.2 CURVE NUMBER METHOD THEORY
This section presents a general description of this methodology, for additional information refer to the National
Engineering Handbook —Section 4: Hydrology (SCS 1985), or the Natural Resource Conservation Service web site
section of hydraulics and hydrology. The amount of runoff from a site calculated using the Curve Number Method
depends on the precipitation at the site and the natural storage capacity of the soil. The curve number equation and the NRCS
rainfall excess equation are shown in Equations 5-1 and 5-2:
Equation 5-1: S = 1000 - 10
CN
42
Where: S = maximum storage volume of water on and within the soil (inches); and,
CN = curve number (dimensionless)
Equation 5-2: Q =(P 0.25)'
(P + 0.8 S)
Q=OforP<0.25
Where: Q = runoff (inches);
S = maximum storage volume of water on and within the soil (inches);
P = precipitation (inches); and,
0.25 = initial abstraction; the fractional amount estimated as intercepted,
evaporated and/or absorbed by the soil (inches).
5.3.3 LIMITATIONS
Alternative methods approved by the City Engineer shall be used when:
• The calculated depth of runoff is less than 0.5 inch;
• The value (P-0.2S) is a negative number; or,
• The weighted CN is less than 40.
For additional limitations, see the Soil Conservation Service's Technical Release No. 55 (Publication 210-VI-TR-55,
Second Ed., June 1986). OC
The City Engineer reserves the authority to limit discharge top blic facilities. Regardless of the methodology used, if
a given method yields a runoff volume or rate that is inconsiste wi the physical site characteristics, the engineer will be
required to provide additional supporting documentation.
5.3.4 BASIN AREAS to% -1(7
The basin area must reflect the actual runoff ch cteristics as closely as possible and be consistent with the
assumptions used. The impervious and pery us areas must be estimated from best available plans, topography,
or aerial photography, and verified by field reconnaissance.
5.3.5 HYDROLOGIC SOIL GROUP CLASSIFICATION
The determination of a site's hydrologic soil group(s) can be found by NRCS Web Soil Survey Web site. The NRCS has
classified over 4,000 soil types into the following four soils groups:
• Group A soils have high infiltration rates, even when thoroughly wetted, and consist chiefly of deep, well -to -
excessively drained sands or gravels. These soils have a high rate of water transmission (greater than 0.30
inches/hour) and low runoff potential.
• Group B soils have moderate infiltration rates when thoroughly wetted, and consist chiefly of moderately fine
to moderately coarse textures. These soils have a moderate rate of water transmission (0.15 to 0.30
inches/hour) and moderately low runoff potential.
• Group C soils have slow infiltration rates when thoroughly wetted, and consist chiefly of soils with a layer that
impedes downward movement of water, or soils with moderately fine to fine textures. These soils have a slow
rate of transmission (0.05 to 0.15 inches/hour) and moderately high runoff potential.
• Group D soils have very slow infiltration rates when thoroughly wetted, and consist chiefly of clay soils with a
high swelling potential, soils with a permanent high water table, soils with a hardpan or clay layer at or near the
surface, and shallow soils over nearly impervious materials. These soils have a very slow rate of transmission
(0-0.05 inches/hour) and high runoff potential.
5.3.6 CURVE NUMBERS (CN)
Curve numbers (CN) indicate the runoff potential of a watershed. The higher the CN value, the higher the potential for
runoff. The CN takes into consideration the hydrologic soil group, land use, and cover.
43
Table 5-1 lists CN values for agricultural, suburban, and urban land use classifications. These values are for Antecedent
Runoff Condition (ARC) II, which is defined below. CN values will need to be converted to ACR III for calculating Water
Quality volumes.
Weighting Curve Numbers:
Basins often include areas with differing curve numbers based on their soils, land use, and cover. Overall CNs for these
basins are determined by weighting the CN for each area based on the size of the area. Weighted curve number method can
be use for flow control and peak flow rate calculation. Water Quality Volume (WQv) calculations shall use the distributed
CN method. Refer to the City Stormwater Quality Management Plan for a detailed description and example on the
distributed CN calculation method.
Antecedent Runoff Condition — Curve Number Adjustment:
The moisture condition in a soil prior to a storm event is referred to as the antecedent runoff condition (ARC). The NRCS
developed three antecedent runoff conditions:
• ARC I (Dry Condition): soils are dry but surface cracks are not evident.
• ARC II (Average Condition): soils are not dry or saturated. The CN values listed in Table 5-1 are applicable under this
condition and do not account for snowmelt or runoff on frozen ground conditions.
• ARC III (Wet Condition): soils are saturated or near saturation due to heavy rainfall or light rainfall and low
temperatures within the last 5 days. ARC III conditions model the winter months.
Table 5-2 shall be used to adjust the CN values from ARC II to ARC III.
Table 5-2
Curve Numbers Based on Antecedent Runoff Conditions (ARC) II
CN ARC II
CN ARC I
CN ARC III
CN ARC II
CN ARC I
CN ARC III
100
100
100
76
58
89
99
97
100
75
57
88
98
94
99
0455
88
97
91
99
73
54
87
96
89
99
72
53
86
95
87
98
71
52
86
94
85
70
51
85
93
83
8
69
50
84
92
81
68
48
84
91
80
977
67
47
83
90
78
96
66
46
82
89
76
96
65
45
82
88
75
95
64
44
81
87
73
95
63
43
80
86
72
94
1 62
42
79
85
70
94
61
41
78
84
68
93
60
40
78
83
67
93
59
39
78
82
66
92
58
38
76
81
64
92
57
37
75
80
63
91
56
36
75
79
62
91
55
35
74
78
60
90
54
34
73
77
59
89
50
31
70
Curve number conversions for different ARC are for the case of initial abstraction (1a) = 0.2 S. Initial
abstraction represents all water losses before runoff begins (water retained in surface depressions, water
intercepted by vegetation, evaporation, infiltration, etc.)
Source: U.S. Soil Conservation Service National Engineering Handbook Table 10.1 (MRCS).
44
Table 5-1
Runoff Curve Numbers
Antecedent Runoff Conditions (ARC) II
Group
Group
Group Group
Cover type and hydrologic condition
A Soils
B Soils
C Soils
D Soils
Open Space (lawns, parks, golf courses, cemeteries, landscaping, etc.): 1
Poor condition (grass cover <50% of the area)
68
79
86
89
Fair condition (grass cover on 501/o to 75% of the area)
49
69
79
84
Good condition (grass cover on >75% of the area)
39
61
74
80
Impervious Areas:
Open water bodies: lakes, wetlands, ponds etc.
100
100
100
100
Paved parking lots, roofs, driveways, etc. (excluding right of way)
98
98
98
98
Porous pavers and permeable interlocking concrete (assumed as 85% impervious and 15% lawn):
Fair lawn condition (weighted average CNs)
91
94
96
97
Gravel
76
85
89
91
Dirt
72
82
87
89
Pasture, Grassland, or Range -Continuous Forage for Grazing:
Poor condition (ground cover <501/o or heavily grazed with no mulch).
68
79
86
89
Fair condition (ground cover 50% to 75% and not heavily grazed)
49
69
79
84
Good condition (ground cover>75% and lightly or only occasionally grazed)
39
61
74
80
Cultivated Agricultural Lands:
Row Crops (good) e.g. corn, sugar beets, soy beans
64
75
82
85
Small Grain (good) e.g. wheat, barley, flax
60
72
80
84
Meadow (continuous grass, protected from grazing and generally mewed for hay
30
58
71
78
Brush (brush -weed -grass mixture with brush the major ele
Poor (<50% ground cover)
48
67
77
83
Fair (50% to 75% ground cover)
35
56
70
77
Good (>75% ground cover)
30
48
65
73
Woods - grass combination (orchard or tree fa
Poor
57
73
82
86
Fair
43
65
76
82
Good
32
58
72
79
Woods:
Poor (Forest litter, small trees, and brush are destroyed by heavy grazing or regular burning)
45
66
77
83
Fair (Woods are grazed but not burned, and some forest litter covers the soil)
36
60
73
79
Good (Woods are protected from grazing, and litter and brush adequately cover the soil)
30
55
70
77
Herbaceous (mixture of grass, weeds, and low -growing brush, with brush the minor element)4:
Poor (<3 0% ground cover)
80
87
93
Fair (30% to 70% ground cover)
71
81
89
Good (>70% ground cover)
62
74
85
Sagebrush with Grass Understory4:
Poor (<3 0% ground cover)
67
80
85
Fair (30% to 70% ground cover)
51
63
70
Good (>70% ground cover)
35
47
55
1 Composite CNs may be computed for other combinations of open space cover type.
2 Actual curve number is less than 30; use CN = 30 for runoff computations.
3 CNs shown were computed for areas with 50% woods and 50% grass (pasture) cover. Other combinations of conditions may be computed from
the CNs for woods and pasture.
4 Curve numbers have not been developed for group A soils.
For a more detailed and complete description of land use curve numbers refer to Chapter 2 ofthe Soil Conservation Service's (NRCS)Technical
Release No. 55 (Publication 210-VI-TR-55, Second Ed., June 1986).
45
5.3.7 TIME OF CONCENTRATION
Time of concentration is affected by the way stormwater moves through a watershed. Stormwater can move in the form of
sheet flow, shallow concentrated flow, open channel flow, or some combination of these. The type of flow should be
verified by field inspection.
The time of concentration for rainfall shall be computed for all overland flow, ditches, channels, gutters, culverts, and
pipe systems. When using the Curve Number Method, the time of concentration for the various surfaces and conveyances shall
be computed using the procedures presented in this section. These procedures are based on the methods described in the
Soil Conservation Service's Technical Release No. 55.
Travel time (Tt) is the time it takes stormwater runoff to travel from one location to another in a watershed. Time of
concentration (T,) is the time for stormwater runoff to travel from the hydraulically most distant point to the point of
discharge of a watershed. T, is computed by adding all the travel times for consecutive components of the drainage
conveyance system as given by the following equation:
Equation 5-3: T� = Tti + Tt,, + ... Tt�
Where: Tc = time of concentration (minutes);
n = number of flow segments; and,
Tt = travel time (minutes) is the ratio of flow length to
flow velocity given by:
Equation 5-4: Tt = L / (60V)
Where: Tt = travel time, in minutes;
L = flow length (feet);
V = average velocity (fe ); and,
60 = conversio (se onds to minutes). Zc
T, influences the shape and peak of the runoff by ograph. Urbanization usually decreases T, thereby increasing the peak
discharge. But T, can be increased as a result of ponding behind small or inadequate drainage facilities including storm
drain inlets and road culverts, or reduction of land slope through grading. T, shall not be less than 5 minutes.
Sheet Flow:
Sheet flow is flow over plane surfaces and shall not be used over distances exceeding 300 feet. Use Manning's
kinematic solution to directly compute Tt
Equation 5-5: Tt= [0.42 (lls L)o.s] / [ (P f.5(S0f.4 ]
Where: Tt = travel time (minutes);
ns = Manning's effective roughness coefficient for sheet flow (use Table 5-3);
L = flow length (feet);
P2 = 2-year, 24-hour rainfall (inches), (use Table 5-5); and,
So = slope of hydraulic grade line (land slope, ft/ft).
The friction value (ns) is used to calculate sheet flow. The friction value is Manning's effective roughness coefficient
modified to take into consideration the effect of raindrop impact, drag over the plane surface, obstacles such as litter,
depressions, crop ridges and rocks, and erosion and transportation of sediment. The ns values are for very shallow flow
depths of about 0.1 foot and are only used for travel lengths up to 300 feet. Table 5-3 gives Manning's ns values for
sheet flow for various surface conditions.
Shallow Concentrated Flow:
46
After 300 feet, sheet flow is assumed to have developed into shallow concentrated flow. The travel time (Tt) for the shallow
concentrated flow segment can be computed using Equation 5-4. The average velocity for shallow concentrated flow
is calculated using the following equation:
Equation 5-6:
Where: V = velocity (feet/second);
k = ks or kc, time of concentration velocity factor (feet/second); and,
So = slope of flow path (feet/foot).
Table 5-3 provides -k- for various land covers and channel characteristics with assumptions made for hydraulic
radius using the following rearrangement of Manning's equation:
Equation 5-7 k 1.49 R 2/3
n
Where: R = hydraulic radius; and,
n = Manning's roughness coefficient for open channel flow
(see Table 5-4).
47
TABLE 5-3
Friction Values (n and k) For Use
In Computing Time Of Concentration
Sheet Flow
ns
Bare sand
0.010
Smooth surfaces (concrete, asphalt, gravel, or bare hard soil)
0.011
Asphalt and gravel
0.0 12
Fallow fields of loose soil surface (no vegetal residue)
0.05
Cultivated soil with crop residue (slope < 0.20 feet/foot)
0.06
Cultivated soil with crop residue (slope > 0.20 feet/foot)
0.17
Short prairie grass and lawns
0.15
Dense grass
0.24
Bermuda grass
0.41
Range, natural
0.13
Woods or forest, poor cover
0.40
Woods or forest, good cover
0.80
Shallow, Concentrated Flow
ks
Forest with heavy ground litter and meadows (n = 0.10)
3
Brushy ground with some trees (n =0.06)
5
Fallow or minimum tillage cultivation (n = 0.04)
8
High grass (n = 0.035)
9
Short grass, pasture and lawns (n = 0.030)
11
Newly -bare ground (n = 0.025)
13
Paved and gravel areas (n = 0.012)
27
Channel Flow (Intermittent, R = 0.2)
k,
Forested swale with heavy ground litter (n=0.10)
5
Forested drainage course/ravine with defined channel bed (n=0.050)
10
Rock -lined waterway (n=0.035)
15
Grassed waterway (n=0.030)
17
Earth -lined waterway (n=0.025)
20
Corrugated metal pipe (n=0.024)
21
Concrete pipe (n=0.012)
42
Other waterways and pipes
0.508/n
Channel Flow (Continuous Stream, R =0.4)
k,
Meandering stream with some pools (n=0.040)
20
Rock -lined stream (n=0.035)
23
Grassed stream (n=0.030)
27
Other streams, man-made channels and pipe
0.807/n
1These values were determined specifically for sheet flow conditions and are not appropriate for conventional open
channel flow calculations.
Source: WSDOT Highway Runoff Manual (2004) Table 4B-5; Engman (1983); and the Florida Department of
Transportation Drainage Manual (1986).
48
Table 5-4
Suggested Values of Manning's Roughness Coefficient "iz"
For Channel Flow
Type of Channel and Description
"n"'
Type of Channel and Description
"n"'
A. CONSTRUCTED CHANNELS
7. Very weedy reaches, deep pools, or
floodways with heavy stand of timber
and underbrush
0.100
a Earth, straight and uniform
1. Clean, recently completed
0.018
2. Gravel, uniform selection, clean
0.025
b Mountain streams, no vegetation in channel, banks
usually steep, trees and brush along banks submerged at
high stages
3. With short grass, few weeds
0.027
b Earth, winding and sluggish
1 No vegetation
0.025
1 Bottom: gravel, cobbles and few
boulders
0.040
2. Grass, some weeds
0.030
3 Dense weeds or aquatic plants in deep
channels
0.035
2 Bottom: cobbles with large boulders
0.050
4. Earth bottom and rubble sides
0.030
B-2 Floodplains
5. Stony bottom and weedy banks
0.035
a Pasture, no brush
6. Cobble bottom and clean sides
0.040
1 Short grass
0.030
c Rock lined
2,41ighgrass
0.035
1. Smooth and uniform
0.035
b ltivated areas
2. Jagged and irregular
0.040
1. p
0.030
d Channels not maintained, weeds and brush uncut
2. Mature row crops
0.035
1. Dense weeds, high as flow depth
0.086
Mature field crops
0.040
2 Clean bottom, brush on sides
0.050
c Brush
3. Same, highest stage of flow
0.070
1 Scattered brush, heavy weeds
0.050
4 Dense brush, high stage
0.100
2 Light brush and trees
0.060
B. NATURAL STREAMS
3. Medium to dense brush
0.070
B4 Minor streams (top width at flood st e < 100
4. Heavy, dense brush
0.100
a Streams on plain
d Trees
1 Clean, straight, full stage, no rifts or
deep pools
0.030
1. Dense willows, straight
0.150
2. Cleared land with tree stumps, no
sprouts
0.040
2 Same as No. 1, but more stones and
weeds
0.035
3. Same as No. 2, but with heavy
growth of sprouts
0.060
3 Clean, winding, some pools and shoals
0.040
4. Heavy stand of timber, a few down
trees, little undergrowth, flood stage
below branches
0.100
4. Same as No. 3, but some weeds
0.045
5. Same as No. 4, but more stones
0.050
6 Sluggish reaches, weedy deep pools
0.070
5. Same as above, but with flood stage
reaching branches
0.120
i The "if 'values presented in this table are the `Normal" values as presented in Chow (1959). For an extensive
range and for additional values refer to Chow (1959)
Source: WSDOT Hyway Runoff Manual (2004) Table 4B-6; Engman (1983) and the Florida Department of
Transportation Drainage Manual (1986).
49
Open Channel Flow:
Open channels are assumed to exist where channels are visible on aerial photographs, where streams appear on United
States Geological Survey (USGS) quadrangle sheets, or where topographic information indicates the presence of a
channel. The k, values from Table 5-3 used in Equation 5-6 can be used to estimate average flow velocity. Average
flow velocity is usually determined for bank -full conditions. After average velocity is computed the travel time (Tt) for
the channel segment can be computed using Equation 5-4.
5.3.8 PRECIPITATION MAPS
The design 24-hour precipitation depths and recurrence interval used by Kalispell are provided in the table below. The
precipitation isopluvial map data comes from National Oceanic and Atmospheric Administration (NOAA) Atlas 2,
Volume IX, 1973.
Table 5-5 City of Kalispell 24-Hour Precipitation Depths
Recurrence
Interval
2 year
10 year
25 year
50 year
100 year
24-Hour
Precipitation Depth
1.4
2.0
2.4
2.8
3.0
(inches)
5.3.9 DESIGN STORM DISTRIBUTION
The CN method requires the selection of, or the input of, a rainfall ution and the precipitation associated with a design
storm. The NRCS Type I 24-hour storm for the 2- 10- and 1 -y ar storm event storm distributions shall be used for
sizing flow control facilities. 71
5.3.10 PEAK DISCHARGE COMPUTATIONS
For a selected rainfall frequency, the 24-hour rainfall 4obmed from NOAA Charts (see Table 5-5). CN value and
total runoff (Q) for the watershed are compute accor in methods outlined in Section 5.3. The CN is used to
determine the initial abstraction (Ia) from eq VL on 5-8.
Equation 5-8: Ia = 0 m 000/CN) — 101
Where:
Ia = initial abstract (inches); and
CN = curve number (dimensionless);
The la/P ratio is a parameter that indicates how much of the total rainfall is needed to satisfy the initial abstraction. The
precipitation value to be used in the ratio is the 24-hr rainfall for the return period of interest. If the la/P ratio is outside the
range of 0.1 to 0.5, then the limiting values should be used; i.e. use 0.1 if less than 0.1 and 0.5 if greater than 0.5. The unit
peak discharge (q) is obtained from figure 5-1. The time of concentration (Tc) and la/P ratio values are needed to obtain
a value for q from the figure.
Equation 5-9: qp = qu A Q
Where:
qp = peak discharge (cfs)
qu = unit peak discharge (cfs/ac/in)
A= drainage area (ac)
Q = runoff (in)
50
Figure 5-1: Unit peak discharge (qu) for NRCS (SCS) type I rainfall distribution
Source MDT Hydrology Manual Chapter 7
0-8
0.7
0.6
0.5
0A
0.10
0.08
0.07
0.06
0.1 0.2 0.3 0A 0.5 0-6 0.7 0.8 0 9 1 5 10
Time of concentration (T,), hours
5.4 LEVEL POOL ROUTING METHOD
This section presents a general description of the methodology for routing a hydrograph through an existing flow control
facility, and for sizing a new flow control facility using hydrograph analysis. The "level pool routing" technique presented here
is one of the simplest and most commonly used hydrograph routing methods. This method is described in Handbook of
Applied Hydrology (Chow, Ven Te, 1964) and elsewhere, and is based upon the continuity equation:
Equation 5-10: Inflow - Outflow = Change in storage
CI1+-+1�=At-SI
2
Where: I = inflow at time 1 and time 2;
O = outflow at time 1 and time 2;
S = storage at time 1 and time 2; and,
At = time interval, time 2 — time 1.
51
The time interval, Q t, must be consistent with the time interval used in developing the inflow hydrograph. TbA t
variable can be eliminated by dividing it into the storage variables to obtain the following rearranged equation:
Equation5-11: Ii+I,+2Si —O, = O�+2S,
If the time intervalQ t, is in minutes, the units of storage (S) are in cubic feet per minute, which can be converted to cubic
feet per second by multiplying by 1 minute/60 seconds. The terms on the left-hand side of the equation are known from
the inflow hydrograph and from the storage and outflow values of the previous time step. The unknowns O, and S, can be
solved using the stage -storage and stage -discharge relationships for the storage facility being analyzed or sized.
5.5 RATIONAL METHOD
The primary source of this section is the MDT Hydrology Manual, Chapter 7. The rational method is an allowable method
for computing peak runoff rates. The rational method can be used for the design of conveyances and flow control
discharge rates.
The peak flow rate is calculated using the following equation:
Equation 5-12: Q, = C I A
Where: Qp = peak flow rate (cfs);
C = runoff coefficient (dimensionless units);
I = rainfall intensity (inches/hour and,
A = drainage area (acres).
Coefficients given in Tables 5-7 and 5-8 are applicable for sto of --yr t 0-yr frequencies. The adjustment of the
rational method for use with major storms can be made by multiply g the right side of the rational formula by a frequency
factor Cf. The rational formula now becomes:
Equation 5-13: Qp = C Cf IA
The Cf values are listed in Table 5-6. The duct of Cf times C shall not exceed 1.0
Table 5-6 Frequency Factors for Rational Formula
Recurrence Interval ears)
Cf
25
1.1
50
1.2
100
1.25
5.5.1 RUNOFF COEFFICIENTS
Table 5-7 and 5-8 provides runoff coefficients. Steeply sloped areas and less frequent, higher intensity storms require
the use of higher coefficients because infiltration and other losses have a proportionally smaller effect on runoff.
Table 5-7
Recommended Coefficient of Runoff for Pervious Surfaces by Selected Hydrologic Soil Groupings and
Slope Ranges
Slope
A
B
C
D
Flat (0-1 %)
0.07
0.10
0.14
0.18
Average (2 - 6%)
0.12
0.15
0.19
0.23
Steep (Over 6%)
0.16
0.21
0.27
0.33
Source: MDT Hydraulic Manual -Chapter 7
Table 5-8
Recommend Coefficient of Runoff Values for Various Selected
Land Uses
Categorized by Surface
Runoff Coefficients
Forest
0.13
Asphalt
0.90
Brick
0.80
Concrete
0.90
Gravel
0.80
Roofs
0.85
Lawns, well drained(sandy soil)
Up to 2% sloe
0.075
2% to 7% sloe
0.13
Over 7% sloe
0.18
Lawns, poor dralned(clay soil)
Up to 2% sloe
0.15
2% to 7% sloe
0.20
Over 7% sloe
0.30
Categorized by Use
Runoff Coefficients
Driveways, walkways
0.80
Unimproved
0.20
Parks
0.18
Cemeteries
0.18
Railroad yards
0.28
Playgrounds
0.30
Business districts
Runoff Coefficients
Neighborhood
0.60
City (business/downtown)
0.83
Residential
Single family
0.4
Multiplexes
0.55
Suburban
0.33
Apartment, Condominiums
0.60
Industrial
Light
0.65
Heavy
0.75
Source: MDT Hydraulic Manual and
Civil Engineering Reference Manual
5.5.2 TIME OF CONCENTRATION
The travel time, the time required for flow to move through a flow segment, shall be computed for each flow segment. The
time of concentration is equal to the sum of the travel times for all flow segments. Refer to the procedure described in
Section 5.3.7 for equations and calculation methods.
The time of concentration shall not be less than 5 minutes. For a few drainage areas, the time of concentration that
produces the largest amount of runoff is less than the time of concentration for the entire basin. This can occur when two
or more basins have dramatically different types of cover. The most common case would be a large paved area together
with a long narrow strip of natural area. In this case, the engineer shall check the runoff produced by the paved area alone to
determine if this scenario would cause a greater peak runoff rate than the peak runoff rate produced when both land
segments are contributing flow. The scenario that produces the greatest runoff shall be used, even if the entire basin is not
contributing flow to this runoff rate.
53
5.5.3 INTENSITY
The rainfall intensity (I) is the average rainfall rate in/hr for duration equal to the time of concentration for a selected
return period. Once a particular return period has been selected for design and a time of concentration calculated for the
drainage area, the rainfall intensity can be determined from Rainfall -Intensity tables. An example of such a table is given
in AASHTO Model Drainage Manual, Chapter 7: figure 7-3; and in Appendix B (adopted by MDT).
54
SECTION 6 - WATER QUALITY
TREATMENT DESIGN
6.1 INTRODUCTION
Water quality treatment facilities are designed to remove pollutants contained in stormwater runoff. The pollutants
of concern include sand, silt, and other suspended solids; metals such as copper, lead, and zinc; nutrients such as nitrogen
and phosphorus; certain bacteria and viruses; and organics such as petroleum hydrocarbons and pesticides. The regulatory
threshold or "trigger" for requiring compliance with this Basic Requirements is outlined in Section 2.1.
The Water Quality design methods are formulated from the City of Kalispell Stormwater Quality Management Plan. This
section presents a general description of the methodology for water quality design; refer to the Stormwater Quality
Management Plan for more detailed descriptions.
Many treatment facilities, when designed correctly, can function as both a water quality treatment facility and a flow
control facility. This section describes design criteria for water quality treatment. Section 7 provides design criteria for
flow control. All treatment facilities in new development and most redevelopment projects shall be on the ground surface.
Underground treatment facilities are not permitted.
6.2 WATER QUALITY PROTECTION STANDARDS
Stream and River Flow Control Standard
• Post development runoff rate shall be limited to no more than 50% of the pre -development 2-year, 24-hour peak
runoff rate (based on SCS Type 1 unit hydrograph), n
• The post development 10-year peak runoff rat shall ben .Lter than the pre -development 10-year, 24-hour peak
runoff rate (based on SCS Type 1 unit hyd ra ).
Wetland Standards
• An on site wetland analysis is required r all new development. See Wetland Analysis in Section 3.4 Drainage
Report; and, 71
• Flow control: See Wetland Flow Control Standards Chapter 6, in the Stormwater Quality Management Plan.
Water Quality Volume (W(?v) Standard
• The water quality volume for the design of BMPS is based on a snowmelt event. The design volume is the runoff
from 1.1 inches of equivalent snow pack moisture. CN values are calculated using the distributed method. See the
Stormwater Quali1y Management Plan for details and example calculations.
6.3 TREATMENT BMPS
Infiltration swales/ponds, wet ponds, biofiltration swale, dry swales, and bioretention facilities can be effective in treating
stormwater runoff. In most cases, soil properties must be appropriate to achieve effective treatment without adversely
impacting groundwater resources. Oil/water separators (OWS) and mechanical treatment devices using hydrodynamic
(vortex) technology can be used to physically separate petroleum products from stormwater. An OWS and mechanical
treatments devises alone do not meet the other treatment goals set forth in this manual. OWS and mechanical treatments
devises may be used in combination with another water quality treatment BMPS, depending upon the site limitations.
This section provides design information and minimum requirements for all treatment BMPS identified in this manual.
In most cases, treatment facilities can be combined with flow control facilities and shall meet all flow controls requirement
in Section 7. All treatment BMP facilities shall be installed upstream of flow control facilities.
Cold and Semi Arid Climate Conditions
55
The Kalispell area climate is both semi and and cold which can affect the performance and the long term maintenance
requirements of flow control facilities and Treatment BMPs.
For semi arid climates, designers should consider the following for each project:
1. Ensure that the permanent pool in wetpond designs can be maintained;
2. Select landscaping plants for wet and drought weather;
3. Use a surface layer of gravel instead of mulch. Mulch deteriorates fast and will need to be replaced more often;
and,
4. Use pretreatment cells or forebays to provide sedimentation due to the high rate of erosion and dust.
For cold climates, designers should consider the following for each project:
1. Select salt -tolerant grasses, shrubs, and tree specie to maintain vegetative cover;
2. Use multiple cells and over size the first pretreatment cell to account to high sedimentation rates;
3. Avoid draining ponds during the spring, as temperature stratification and high chloride levels may discharge acidic
or anoxic water downstream;
4. Do not submerge inlet pipes into permanent pools to avoid causing pipe ice blockage;
5. Extend the soil filter media below the frost line;
6. Slope pipes a minimum of 1% or 2% to prevent standing water from freezing;
7. Underdrains should be place at least a foot below the frost line and increase the perforated pipe diameter by at
least one pipe schedule. The minimum opening diameter hole for perforated pipes should be '/2 inch; and,
8. Consider snow storage in the design.
6.3.1 INFILTRATION BASINS
An infiltration basin is a practice that discharges surface water int e derlying soil.
Pretreatment
• Pretreatment is required for urban watersheds when 15° o or more of the area is impervious surface:
o Pretreatment volume shall be equal to 20% of WQv. The pretreatment volume is in
addition to the infiltrati ba in's Qv sizing requirement.
Groundwater
• The bottom of the basins shall be at least 3 eet above the seasonal high groundwater table:
o The seasonal high watetable shall be based on long-term piezometer records during at
least one wet season or the mottled soil layer as determined by a licensed geologist,
licensed engineer with geotechnical expertise, or hydrogeologist.
Access and Setbacks
• Minimum infiltration basin setback restrictions:
o Building Foundations: At least 20 feet upstream and 50 feet downstream of infiltration basins;
o Back from top of slope greater than 15%: At least 50 feet or as determined by a licensed
engineer with geotechnical expertise;
o Septic drain fields: At least 50 feet;
o Shallow water supply wells (typically individual homeowner wells): At least 100 feet;
o Easement or property line: 20 feet; and,
o Floodplain: Outside 10-year High Water Level (HWL).
• Provide dedicated maintenance access route to infiltration basin from a public roadway. Access route to be
dedicated by maintenance easement or tract.
Infiltration Criteria
• Short-term infiltration rate: The short-term soil infiltration rate shall be a minimum of 0.5 inches/hr and a
maximum of 20 inches/hr.
o Short-term infiltration rate determination: The requirements and procedures to conduct infiltration
tests are described in Section 4; and,
o Reduction factors: The reduction factor is applied to the measured short-term rate. A
reduction factory of two (2) shall be used in determining the long-term infiltration rate below.
56
Long-term soil infiltration rate determination: The long-term infiltration rate is the estimated short-term rate with
an applied reduction factor. The reduction factor is to account for measurement uncertainty, site variability,
fluctuation of infiltration rate with water levels, pretreatment for total suspended solids (TSS) control and degree of
maintenance that together affect long-term infiltration rates:
o Long-term infiltration rate: Divide short-term rate by total reduction factor (RF) to determine the
design long-term infiltration rate.
An infiltration rate of 0.5 inches/hr to 2.5 inches/hr is typical for soil textures that possess sufficient physical and
chemical properties for adequate treatment. When the Long-term infiltration rate is greater than 2.5 inches/hr a
site specific analysis shall be performed to determine pollutant removal to prevent groundwater
contamination. The maximum infiltration rates for the various soil types are outlined below in table 6-1.
The maximum rate used to calculate the design infiltration rate shall be the lesser of the values in Table 6-1
and the Long-term infiltration rate.
Table 6-1: Maximum Infiltration Rates for Soil Types
Soil Texture Class
Infiltration Rates
Coarse sands, cobbles
20
Medium sand
8
Fine sand, loamy sand
2.4
Sandy loam
1
• Infiltration basin drawdown time: Designed to drain dry ithin 72 hours after the design event using the
long term soil infiltration rate: Infiltration basins will nee t e refreshed and infiltration rate restored when the
actual draw down time to drain dry exceeds 72 hours.
Planting Requirements
• Plant basin with native vegetation containing a mixt e cies of varying moisture tolerances. See Section 7 for
planting guidelines.
Post Construction Verification
• Submit post -construction verificatio volume nd infiltration capacity:
o Submit an as -built grading plan of the infiltration basin after construction to the City to verify the
design storage volume has been provided; and,
o Perform post -construction testing of actual short-term infiltration rates to ensure the basin
functions as designed or corrective action will need to be taken. Refer to Section 4 Appendix 4A
Pond Flood Test.
6.3.2 OIL/WATER SEPARATORS (OWS)
Oil Water Separators (OWS) shall only be used in redevelopment situations where other City approved treatment
BMPs outlined in Section 6.3 are not conducive to the site. OWS are a pretreatment and are only effective in achieving
oil and total petroleum hydrocarbons (TPI) removal when regular maintenance is provided. Without proper sludge,
oil, and sediment removal, there is a high potential for clogging which can impair the long-term efficiency of the
separator.
Two types of oil water separators (OWS) are included in this manual:
• Baffle types; and,
• Spill control separators, such as a T or elbows located inside a catch basin.
Detailed design information for baffle type OWS can be found in Appendix 6A.
Oil/Water Separator Minimum Requirements
The following are design criteria applicable to spill control separators:
• "T" or elbow separators in a catch basin are not allowed as an oil control device unless used in series with another
water quality treatment facility.
57
The following design criteria are applicable to baffle type oil/water separators:
• Oil control shall occur prior to dispersal into or through a water quality BMP or flow control facility;
• Where applicable, locate the separator off-line and bypass flows in excess of the water quality design flow
rate;
• Follow industry standards such that the separator has a forebay, separator section, and afterbay;
• Design the surface area of the forebay at 20 square feet per 10,000 square feet of area draining to the separator;
• The length of the forebay shall be one-third to one-half the length of the entire separator;
• Include a submerged inlet pipe with a turned -down elbow in the forebay at least two feet from the bottom; the outlet
pipe shall be a "T" sized to pass the design peak flow and placed at least 12 inches below the water surface;
• Size the separator bay for the water quality design flow rate;
• Include a shutoff mechanism at the separator outlet pipe;
• Use absorbents and/or skimmers in the afterbay as needed;
• Oil retaining baffles (top baffles) shall be located at least a quarter of the total separator length from the outlet and
shall extend down at least 50% of the water height and at least 1 foot from the separator bottom; and,
• Baffle height to water depth ratios shall be 0.85 for top baffles and 0.15 for bottom baffles.
6.3.3 WETPONDS
A wet ponding basin is a basin that maintains a significant pool of water (wet pool or dead storage) between runoff events.
The volume of the wet pool is the WQv. Refer to Section 6.2 to calculated WQv.
Peak flow control (detention) can be provided in the live storage area above the permanent pool. Figure 6.2 and 6.3
illustrate a typical wetpond BMP.
Wetpond Geometry
• The wetpool shall be divided into two cells separated e first cell shall contain between 25 to 35
percent of the total wetpool volume. The berm vol e sh t count as part of the total wetpool volume;
• Wetpond may be single cells when:
o Wetpool volumes less than or e o 4, 00 cubic feet; and,
o Length to width ration is > 4:1.
• Depth:
o Sediment storage shall e ovi the first cell. The sediment storage shall have a minimum depth
of 0.5 feet. The sediment sto olume shall not count as part of the total wetpool volume;
o Minimum average pool depth elow outlet elevation) at least 3 feet; and,
o Maximum pool depth (below outlet elevation) less than or equal to 8 feet.
• Length: Promote residence time (length before water in basin is replaced with new inflow) within the basin and
associated pollutant removal efficiency through the following;
o Design basins with a 3:1 length to width ratio or greater; and,
o Separate inlet pipes and outlet pipe to the greatest extent feasible to prevent "short circuiting" and
promote "plug flow" through the basin.
• Slopes: Criteria for side slopes are given in Section 7.7:
0 3 H: IV basin slope can be used in the wetpool area when the design conforms to the typical bench
detail outlined in Figure: 6-1; and,
0 Grade basin slopes at 5:1 or shallower where infiltration or evaporation is expected to result in
significant fluctuation in water levels during the summer months to improve aesthetics (avoid the dry
bathtub look) and allow native vegetation to hide some of the water level fluctuation.
Figure 6.1
MAa+`E`�E `�, 8 CY Class 1 Rip Rap
(Not Required)
/ AQUATIC VEOETATIDM HEM]f
YPICAL SIDE SLOE PRUME
SIDE SLOPE PRUFRE
�YITNQI W OP SKIMMER 17 PONY Outlet Ek. ,
OVRET PIPE
TYPICAL BENCH DETAIL
WITHIN 10' OF SKIMMER OUTLET
MAINTENANCE aENCH
(Not Required)
a —
TYPICAL BENCH DETAIL
Berms
• A berm shall extend across the full width of the we o ,and tie into the wetpool side slopes. If the berm
embankments are greater than 4 feet in height, the berm must be constructed by excavating a key equal to 50 percent
of the embankment cross sectional height and widths. This requirement may be modified if authorized by a
geotechnical engineer based on specific si e conditions;
• The top of the berm may extend to the WQv design water surface or be one foot below the WQv design water
surface; and,
• If the top of berm is at the WQv design wailer surface, berm side slopes must be 3H: IV. Berm side slope may be
steeper (up to 2:1) if the berm is submerged one foot and is approved by a geotechnical engineer.
Outflow Control Structures
• Outlet structure shall be provided either as a manhole with a restrictor device or a skimmer in front of the outlet
pipe. Refer to the Section 7.4 for details of approved outflow structures; and,
• Dissipate flow energy and erosion potential at pipe outlets, typically using riprap.
Groundwater
• Wet ponds work best when the water already in the pond is moved out by incoming flows called "plug flow."
Because treatment works on this displacement principle, the dead storage pool of wetponds may be provided below
the ground water level without interfering unduly with treatment effectiveness. However, if combined with a
detention function, the live storage must be above the seasonal high ground water level; and,
• Buffer the interaction between surface runoff and groundwater for those ponding basins excavated below the
groundwater table. Install a liner of clay topsoil 1-foot thick along the basin bottom up to one foot above the outlet
elevation as the buffer, if needed.
Planting Requirements
• Seed pond basin slopes with native seed mix containing a mixture of species of varying moisture tolerances. See
Section 7 for planting guidelines.
59
Access and Setbacks
• Minimum wet ponding basin setback restrictions:
o Back from top of slope greater than 15%: At least 50 feet or as determined by a licensed engineer with
geotechnical expertise.
• Floodplain: Outside the 10-year High Water Level (HWL).
o Intent is to minimize routine flooding of basins and to avoid them from ending up as part of a stream if
the channel meanders.
• Provide a dedicated maintenance access route to wetpond basin from the public roadway. Access route to be
dedicated by maintenance easement or drainage tract.
Post Construction Verification
• Submit an as -built grading plan of the ponding basin after construction to the City verifying that the design water
quality and flood control volumes have been provided.
Design Considerations
• Wetpond treatment BMPs are not recommended for projects that discharge to trout bearing streams. Wetpond
discharge could lower the temperature and decrease the Dissolve Oxygen level in the stream.
60
Figure 6-2 Wet Pond Plan Vied
` �-- inlet pipe & catch basin per
access road to inlet structure
j detention facility requirements
r,
FIRST WETPOOL CELL
berm or baffle at design
25% to";C Yf ::trnci vK;ur*ie,
WS or submerged 1'
, ,
below design W.S.
Extend berm across entire
wetpool width.
berm top width' min. ; ;
�,
SECOND WETPOOL CELL
WQ design WS ;
"
`;
overflow WS I
wet ool
width
emergency overflow WS ; ;
; ; plantings required on cut
B slopes
emergency spillway per
detention facility requirements
manhole & outlet pipe pie
sized to pass peak flow per
conveyance requirements
---------'
•�
-
-
-- "
4
access road to outlet erosion control &
`
outlet structure energy dissipation per
'`•.,
detention facility requirement:
o
B
NOTE: Berm not required for ponds
PLAN VIEW
with length to width ratio >_ 4:1
or if volume less than 4000 0.
NTS
01
Figure 6-3 Wet Pond Profile Vied-
ERM EMBANKMENT
CONTROL STRUCTURE- r iTOP WIDTH OF BERM
EMERGENCY OVERFLOW
POND OVERFLOW WI II 100 YR 24-HR �_ 'J ^-- ","
r
POND DESIGN WS g 10 YR 24-HR ` EMERGENCY
p" �n OVERFLOW SPILLWA
POND DESIGN W F --
MIN. 6'
ENT STORAGE VALVE MAY BE LOCATED
INSIDE MH OR OUTSIDE
WITH APPROVED OPERATIONAL ACCESS
GRAVITY DRAIN
8' MIN DIAMETER
SECTION A —A
NTS
IN
IOL
NOTES: SiLUIIUN 13-13
SEE DETENTION FACILITY NTS
REQUIREMENTS FOR
LOCATION AND SETBACK
REQUIREMENTS
62
6.3.5 BIOFILTRATION SWALES
A biofiltration swale is an open, gently sloped, vegetated channel designed for treatment of stormwater. The primary
pollutant removal mechanisms are filtration by grass blades which enhance sedimentation and trapping and adhesion of
pollutants to the grass and thatch.
Application and Limitations
• Biofiltration swales do not provide flow control but can convey treated runoff to flow control facilities.;
• Biofiltration swales shall be designed so that stormwater will flow evenly across the entire width of a
densely vegetated area;
• Biofiltration swales shall be applied to small scale projects of 5 acres or less;
• Biofiltration swales shall not be located in shaded areas;
• Stormwater runoff carrying high concentration of oil and grease impairs the treatment capability of the
swale; Oil control options shall be applied as pretreatment in this situation;
• Biofiltration swales shall be designed to be dry between storm events; and,
• The swale shall not receive continuous base flows or be located in a high groundwater area.
Groundwater
• The bottom of the basins shall be at least 3 feet above the seasonal high groundwater table:
o The seasonal high water table shall be based on long-term piezometer records during at
least one wet season or the mottled soil layer as determined by a licensed geologist,
licensed engineer with geotechnical expertise, or hydrogeologist.
Access and Setbacks
• Biofiltration swales shall meet the minimum setback req ' ements specified in Section 7; and,
• Provide dedicated maintenance access route to the biofiltration swales from a public roadway. Access route to be
dedicated by maintenance easement or trac
Biofiltration Design
• Design flows: The swale design is b o e Water Quality Design Flow (Qwq). The Qwq is calculated
using the peak flow rate associated wi e runoff Water Quality Volume of 1.1 Inches. See Section 6 for
water quality protection standards;
• Swale Bottom Width: Determine the bottom width of the swale using equation 6-1 or 6-2;
Equation 6-1: Q=1.486AR'S'
n
Where: Q = rate of flow (cfs);
A = cross -sectional area of flow in the channel (square feet);
R = hydraulic radius (feet); where R = A/P, P = wetted perimeter (feet);
S = channel longitudinal slope (feet/foot); and,
n = Manning's roughness coefficient (Table 5-4).
For a trapezoidal channel with shallow flow, the hydraulic radius can be approximated to the depth of flow. Using
this assumption, the following can be used to solve the required width:
Equation 6-2: b = nEQ—Dwq_ - Zy
1.486 y5/3 sv2
Where: Qwq = rate of flow (cfs);
y = depth of flow (feet) (4 inches max for sod);
Z = side slope of the strip in the form Z:1;
63
b = bottom width of strip (feet);
S = channel slope (feet/foot); and,
n,,,n = Manning's roughness coefficient for shallow flow conditions = 0.20
(unitless)
• Calculate design flow velocity through the swale;
Equation 6-3: Vwq = Qvq
A,,,q
Where: Vwq = design flow velocity (fps)
Q = water quality rate of flow (cfs);
Awq= by + Zy' = cross sectional area (sf) of flow at design depth; and
Z = side slop of the strip per unit height (e.g., Z = 3 if side slopes are 3H:1V).
• Calculated the length of the swale: The minimum channel length is 100 feet unless the width is increased
per the minimum geometry requirements in the following minimum requirements. Use the following
equation to determine the necessary swale length to achieve a hydraulic residence time of at lease 9
minutes (540 seconds).
Equation 6-4: L = 540 Vwq
Where: Vwq = design ,flow velocity (fps); and,
L = minimum allowable swale length (ft).
Minimum Requirements 40amOM7
• The biofiltration channel shall have a minimum length of 100 feet. The length shall not be reduced such that
the minimum residence time and/or maximum flow depth criteria are violated;
• The maximum bottom width is 10 feet and the minimum width is 3 feet. If the calculated bottom width
exceeds 10 feet, parallel biofiltration channcfs shall be used in conjunction with a device that splits the flow
and directs an equal amount to each channel;
• The ideal cross-section is a trapezoid with side slopes no steeper than 3:1. However, a rectangular shape can be
proposed if there are topographical constraints or other construction concerns;
• Typically, the depth of flow shall not exceed 4 inches during the design storm. The depth of flow is 4
inches for sod and 3 inches for dryland grasses;
• The channel slope shall be at least 1% and no greater than 5%. Slopes of 2% to 4% provide the best
performance. When slopes less than 2% are used, an under -drain is required. A 6-inch-diameter perforated
pipe shall be installed in a trench lined with filter fabric and filled with 5/8-inch minus round rocks. The
pipe shall be placed at least 12 inches below the biofiltration channel bed and the bed shall incorporate topsoil
that has a proportionately high sand content. See the Figure 6-5 Biofiltration Swale Underdrain Detail;
• The maximum flow velocity through the swale under water quality design flow conditions shall not
exceed 1 foot/second and the design shall provide for a 9 minute residence time;
• The maximum flow velocity through the swale under peak 100-year flow conditions shall not exceed 3
feet/second; and,
• A flow spreader shall be used at the inlet of a swale to dissipate energy and evenly spread runoff as sheet
flow over the swale bottom. Flow spreaders are recommended at mid -length of the swale. For detail on
flow spreaders see Appendix 6B.
Planting Requirements
• Grass shall be established throughout the entire treatment area of the Swale;
• Irrigation is required during the first summer following installation if seeding occurs in spring or summer;
64
• A newly constructed swale shall be protected from stomwater flow until grass has been established. This may be
done by diverting flows or by covering the swale bottom with clear plastic until the grass is well rooted. If these
actions are not feasible, an erosion control blanket shall be placed over the freshly applied seed mix; and,
• Swale treatment areas are subject to both dry and wet conditions, as well as accumulation of sediment and debris.
A mixture of dry -area and wet area grass species that can continue to grow through silt deposits is most effective.
A list of grass seed mixes is located in Appendix 7.
Figure 6-4 Boifiltration Swale Schematic
sti s
mQi"nanae a4oeae rid
N, Inlet
(modular grid pavement
powus p2w9n mnt, asphalt,
ry'r
ooncrele or gravel) for
tip{
WhbVle P=
ilow spreader
wid-swarle
stow 5preaoef
;recommended �
bioRltredon swan bottom
(min. swage length=IGO fl.)
Note: Longitudial slope 1-5%
Provide underlain for slopes < 2%
I
PLAN
NTS
roadway length depends an
swala area (see la, tj
"ClWet
65
Figure 6-6 Boifiltration Swale Underdrain Detail
Underdarin for slopes < 2%
6" minumum admended soil
�. swam t�llom
4
perlpral" ur4erdr*n
SECTION plpe centered Irendalfl Swale
NTS 5!S mirm Glean drain ruck
finer faunc
NOTE: Undee&airl r6usi in5lbrabe or drain
rrut 1* ip *r` ac Gmptable dircharge point.
5HBriebrir wrap
flI lop, rides and baltom
6" min. amended soil
�a 6" min. oMer C+pe
perforated pipe undercrain
Ecentered beneath awele
_06ginal soil
DETAIL A
6.3.6 CONTINUOUS INFLOW BIOFILTRATION SWALES
In situations where water enters a biofiltration swale continuously along the side slope rather than discretely at the head, a
different design approach -the continuous inflow biofiltration swale-is needed. The basic swale design is modified by
increasing swale length to achieve an equivalent average residence time. For the most part, the specification listed in
section 6.3.4 Biofiltration Swales are the same for Continues Inflow ltration Swales except for the following
modifications.
Application and Limitations
• Continuous inflow swales are to be used when inflows not concentrated such as locations along the
shoulder of a road without curbs. This design may also be used when frequent small point flows enters a
swale. In general, no inlet port should cy- y more than 10% of the flow; and,
• Continuous inflow swales shall not be used for a situation in which significant lateral point flow enters a
swale at some point downstream fr head of the swale.
Biofiltration Design
• The design flows from continuous inflo swales must include runoff from the pervious side slopes draining
to the swale along the entire swale length;
• The method of analysis for continuous inflow swales is the same as for basin biofiltration swales (see
Section 6.3.4) except for the following:
o The WQ design flow may be variable to reflect the increase in flow along the swale length.
If only a single design flow is used, the flow at the outlet shall be used; and,
o Double the hydraulic residence time so that it is a minimum of 18 minutes (1080 seconds).
Equation 6-5: L =1080 Vwq
Where: Vwq = design flow velocity (fps); and,
L = minimum allowable swale length (ft).
Planting Requirements
• Interior side slopes above the WQ design treatment elevation shall be planted in grass. A typical lawn seed mix or
the biofiltration seed mixes are acceptable. Landscape plants or ground covers other than grass shall not be used
anywhere between the runoff inflow elevation and the bottom of the swale.
6.3.7 BIORETENTION AREAS
Bioretention areas are stormwater quality BMPs that capture and temporarily pond the water quality volume (WQv) in
shallow basins or landscaped areas. The WQv is then rapidly filtered through a filter bed material to remove pollutants
from stormwater runoff. The filtered runoff is typically collected and returned to the down gradient conveyance system,
though it can also infiltrate into the surrounding soil in areas with permeable soils and low ground water.
Bioretention areas are also known as "rain gardens" when used on individual residential lots, often without and underdrain.
Bioretention creates a good environment for runoff reduction, filtration, biological uptake, microbial activity, and provides
high pollutant remove.
Three scales of bioretention systems, based on contribution drainage area (sf), are defined for this specification:
1. Micro-bioretention (250 to 2500 sf);
2. Small scale bioretention (2,500 to 26,000 sf); and,
3. Bioretention basins (20,000 to 200,000 sf).
Application and Limitations
• Bioretention systems shall not be designed to provide flow control. An overflow structure or a flow splitter
structure shall be provided to convey flow from storms larger than the WQv to flow control facilities;
• Bioretention systems shall be applied to small-scale projects of 5 acres or less. Multiple filtering systems can be
used for larger areas;
• Stormwater runoff carrying high concentration of oil and grease impairs the treatment capability. Oil control
options shall be applied as pretreatment in this situation;
• Bioretention systems are susceptible to clogging by sediment d therefore pretreatment is a necessary part of the
design;
• Bioretention systems should not receive continuous base flows or be located in a high groundwater area; and,
• The minimum head or elevation difference needed at a site from the inflow to the outflow underdrain or pea gravel
under -layer is typically 5 feet.
Groundwater
• The bottom of the basins shall be at least 3 feet abov e seasonal high groundwater table;
0 The seasonal high water table shall be base on long-term piezometer records during at least one wet
season or the mottled soil 1 r as determined by a licensed geologist, licensed engineer with
geotechnical expertise, or by eologist.
soils
For bioretention areas placed in subsoils having a hydrologic soil group designation of B, C, or D, an underdrain
system is required; and,
Designs shall verify soil permeably by using on -site soils testing outline in Section 4. A soil testing is not required
when an underdrain system is installed.
Underdrains
Underdrains shall be included in the design when subsoil infiltration rates are below 1.0 inch/hr;
When an underdrain is required a minimum 6-inch-diameter perforated pipe shall be installed in a trench lined
with filter fabric and filled with a foot depth of clean pea gravel;
o The pipe spacing shall be at a maximum of 10 feet on center and a minimum grade of 0.5% must be
maintained; and,
o A permeable filter fabric or sand layer shall be required between the gravel layer and the planting soil
bed.
• All underdrain systems shall be day -lighted to an outfall structure.
Filter Media
Planting soils media shall consist of a sandy loam, loamy sand, or loam texture per USDA textural triangle with a clay
content ranging from 0 to 5%. In addition, the planting soil must have a 3 to 5% organic content.
• The recommended planting soil media mixture is:
0 85 — 88 % sand. (washed medium sand is sufficient)
0 8 - 12 % fines. (Includes both clay (max 5%) and silt
67
0 3 -5 % organic matter (leaf compost or peat moss)
• Small scale bioretention and bioretention basin designs shall use premixed certified media from a vendor that
meets the following requirements for phosphorus contend, cation exchange (CEC), and media filtration;
o The recommend P-index value is between 10-50;
o Soils with CECs exceeding 10 are preferred for pollutant removal; and,
o The medial should have an infiltration rate of 1 to 2 inches per hour
• Micro-bioretention (250 to 2500 sf) soil media can be mixed on site;
• The minimum filter media depth shall be between 30 to 48 inches; and,
• Filter media shall be placed in lifts of 12 to 18 inches.
Surface Cover
• Bioretention system shall have a 2 to 4 -inch landscape layer placed above the filter media to protect the soil bed
from erosion. The landscape layers include the following:
o Mulch: Mulch enhances plant survival, suppresses weed growth, and pre -treats runoff before it reached
the filter media. Shredded, aged, hardwood bark mulch makes a very good surface cover;
o Turf grasses; Turf grasses (fine fescue, tall fescue) are typical used for micro bioretention applications
such as front yards; and,
o River stone or pea gravel: Stone or gravel are not recommended in parking lot application since the
increase soil temperatures and have low water holding capacity.
Pretreatment
Pretreatment of runoff entering the bioretention area is required to trap coarse sediment particles before they reach the filter
bed. Pretreatment measures shall be designed to evenly spread runoff ss the entire width of the bioretention area.
Several pretreatment measures are feasible, such as: a grass filter st low a flow spreader, a grass channel, or a pea
gravel diaphragm. The following are approved pretreatments op , s;
• Micro-bioretention (250 to 2500 sf):
0 A grass filter strip extending a minimum of 10 ft the edge of pavement and a maximum slope of 5%.
• Small scale bioretention (2,500 to 20,000 sf):
o A grass filter strip with a pea gravel diaphragm r other flow spreader. The required length of the filter
strip depends on the drainage area, impervio sness, and the filter strip slope. Design guidance on filter
strips for pretreatment can be found in Appendix 6C;
o A grass channel with a pea gravel diaphragm or other flow spreader. The length of the grass channel
depends on the drainage area, land use, and channel slope. The minimum grassed channel length shall be
20 feet. Design guidance on grasechannels for pretreatment can be found in Appendix 6C; and,
o A Pretreatment Cell, see the description below.
• Bioretention basins (20,000 to 200,000 sf):
0 A Pretreatment Cell, similar to a forebay, is located at the piped inlets or curb cuts leading to the
bioretention area and has a storage volume equivalent to at least 15% of the total WQv. The design shall
have a 2:1 length to width ratio. The cell can be formed by a wooden or stone dam or rock berm.
Design Method Criteria
• Ponding Area: The ponding area provides for surface storage of stormwater runoff before it filters through the
filter bed. The ponding area shall contain the entire volume associated with the runoff Water Quality Volume of
1.1 Inches. The ponding depth shall be designed to be 6 to 12 inches above the filter bed; and,
• Filtering Treatment Criteria: The filtering bed shall have a minimum depth of 30",
o The planting soil filter bed shall be sized using a Darcy's Law equation with a filter bed drain time of 48
hours and a coefficient of permeability (k) of 0.5 ft/day.
o The required filter bed area (At) is computed using the following equations:
Equation 6-6: A f = (WQv) (df) / [(k) (hf + df) (tf)]
Where: Af = surface area of filter bed (ft2);
WQv = water quality volume (ft3);
df = filter bed depth (feet);
k = coefficient of permeability of filter media (ft/day);
hf = average height of water above filter bed (ft); and,
tf = design filter bed drain time (days).
Minimum Requirements
• The filter bed surface should general be flat so the bioretention areas are fills up like a bathtub;
• Do not use heavy equipment in the bioretention basin;
• Observation wells and cleanout pipes should be included in the design if their contributing drain area exceeds 1
acre. The well should be tied into any T's or Y's in the underdrain system, and should extend upward to be flush
with the surface and with a vented cap; and,
• Bioretention areas can be used for snow storage as long as an overflow is provided and they are planted with salt
tolerant, non -woody plant species. Tree and shrub locations cannot conflict with plowing and piling of snow into
storage areas.
Access and Setbacks
Bioretention systems shall meet the minimum setback requirements specified in Section 7; and,
Provide dedicated maintenance access route to the facility from a public roadway. Access route to be dedicated by
maintenance easement or tract.
Planting Requirements
• A dense vegetative cover shall be established over the contributing drainage area before runoff can be accepted
into the facility;
• A landscape plan shall be provided for the bioretention area in the drainage report;
• Surface sand filter layers shall have a grass cover to aid in pollutant adsorption. The grass should be capable of
withstanding frequent periods of inundation and drought; I&'
• The filter media soil bed shall be at least 4 feet in depth when trees are planted in the bioretention area but can be a
minimum of 2.5 feet deep in facilities that will utilize plants other than trees;
• Planting recommendations for bioretention facilities can be tbund at the Montana Natural Resource Conservation
web site at http://www.mt.nres.usda. og_v. It is highly recomlnded that the planting plan be prepared by a
qualified landscape architect
o Native plant species should be sp�cified over non-native species;
o A selection of trees with an understory of shrubs and herbaceous material should be provided;
o Woody vegetation should not be specified at inflow locations;
o Trees should be planted primarily7alng the perimeter of the facility;o Plants should be selected base oncified zone of hydric tolerance and must be capable of surviving
both wet and dry conditions; and,
o "Wet footed" species should be planted near the center, whereas upland species are better near the edge.
Maintenance Criteria
• The maintenance access shall be designed such that all areas of the bioretention area can be easily accessed, and
shall be designed to allow vehicles to turn around;
• A maintenance right-of-way or easement shall be provided from a driveway, public or private road. The
maintenance access shall have a minimum unobstructed drive appropriately stabilized to withstand maintenance
equipment and vehicles;
• Maintenance for bioretention areas shall meet the requirements set in Section 10-, and,
• Successful establishments of bioretention areas requires certain tasks be undertaken in the first year;
o Initial inspections: For the first six months following construction, the site should be inspected a least
twice after storm events that exceed a half —inch;
o Spot Reseeding: Inspector should look for bare or eroding areas in the contributing drainage or around
the bioretention area, and make sure that they are immediately stabilized;
o Fertilization: One-time, spot fertilization may be need for initial plantings;
o Watering: Watering is needed once a week during the first two month, and then as need during the first
growing season, depending on rainfall; and,
o Remove and replace dead plants: Since up to 10% of plant stock may die off in the first year,
construction contracts should include a care and replacement warranty to ensure vegetation is properly
established and survives during the first growing season following construction.
Figure 6-6 Bioretention Area
PARKING LOT SHE ET FLOW
1
CURBSTOPS }
SAND DIAPHRAGM
wl. wl.L +k 4%V%V Jk 4141....... •k •k J•J•J• J•J•J-I I I II I I I I I I J•4 J. J. +k
LJiJt •A•J•J•EYEYEY•YJ•J•J•J• J•J•J• J• J• �l+•l+ J+J+J•I I I I I I I I I I I I L LJ•J•
GRASS FILTER STRIP
V• w J+J•.......J•....
4•Jf•4••4••4••4•J•J•J•J•J•J•J•J•J•yyyyJ' J'��J•J I I I I I I I I I I ,L
J'J'J'J'J•J•J•yyyyyyIlk, Ilk, PIP 414,
4-4-4k4 J•yyy 4, 4• 4, 4•++ J• J• J• J + + J•J•J•J•+4 1 1 1 1 1 1 1 1 1 J-j,
���1 IV IV ��yy yyyJ-yy yyyy y J:��yyyy��y�y
w.r.r.r.rw5lesvJ• 1�.�r•r•.w.wwww
OUTLET
OVERFLOW—"""
VERFLOW BERM -
-CATCH BASH'
UNDERDRAIN COLLECT10N SYSTEM
PLAN VIEW
CURB STOPS
f STONE DAPHRAG61
tI WQv —
_III
I -
L li�l_
8• PONDINr=
2'-3•MULCH—
V WQv —
2.5' TO 4'
FILTER MEDIA
FILTER FABRIC
6"PERFORATED
PIPE IN 12"
GRAVEL JACKET
TYPICAL SECTION
7k. -N IEl
I'•��
� I E r 1Tr
Figure 6-7 Bioretention Area Off-line Schematic
PROFILE
7il
u�a•
+ +ut �� u
TO REOEAfNG
WATERS
—AT
u=-a
BIOR
'DRAIN
OVERFLOW. BYPASS
FLOW PATH
VEGETATED PRETREATMENT
BIOFLETENTION AREA
VEGETATED PRETREATMENT
(GRASSEDSWALE)
PEAGRAVEL DIAPHRAGM
(2 x 1'x CURB SLOT WIDTH)
SLOPE TO
DRAIN
MAX. PONDING LIMIT
(TEMPORARY UNUSABLE
PARKING STALLS)
—SLOTTED CURB. SIZED TO PASS:
O peak FRO M WOV (= 1.5' ! MP. ACR Ej
MAX. PONDING DEPTH=6-
7�7
i - OVERFLOW
-BYPASS'
— P x 1' PEA GRAVEL DIAPHRAGM
(FOR INLETPROTECTIONIPRETREATMENTi
6.3.8 DRY SWALES
Dry swales are essentially shallow bioretention cells that are configured as a linear channel. The dry swale is a vegetated
conveyance channel designed to include a filter bed of prepared soil that overlays an underdrain system. Dry swales are
sized to allow the entire WQv to be filtered or infiltrated through the bottom of the swale. The filtered runoff is typically
71
collected in an underdrain and returned to the down gradient conveyance system, though it can also infiltrate into the
surrounding soil in areas with permeable soils and low ground water. Dry swales are well suited to treat highway or low
and medium density residential road runoff and along margins of small parking lots.
Application and Limitations
• Dry swales shall not be designed to provide flow control. Dry swales are an on-line practice and must be designed
with enough capacity to convey runoff for the peak 10 year and 100 year storm events and be non -erosive for the
peak 2 year storm event. An overflow structure or a flow splitter structure can be provided to convey flow from
storms larger than the WQv to flow control facilities;
• Dry swales shall be use on sites with longitudinal slopes of less that 4%;
• Dry swale systems shall be applied to small-scale projects of 5 acres or less;
• Stormwater runoff carrying high concentration of oil and grease impairs the treatment capability. Oil control
options shall be applied as pretreatment in this situation;
• Dry swale systems are susceptible to clogging by sediment and therefore pretreatment is a necessary part of the
design;
• Dry swales shall be designed so that stormwater will flow evenly across the entire width of a densely
vegetated area;
• Dry swales should not receive continuous base flows or be located in a high groundwater area; and,
• The minimum head or elevation difference needed at a site from the inflow to the outflow underdrain or pea gravel
under -layer is typically 3 to 5 feet.
Groundwater
• The bottom of the basins shall be at least 3 feet above the se al high groundwater table:
0 The seasonal high water table shall be based on 1 g piezometer records during at least one wet
season or the mottled soil layer as determined lice geologist, licensed engineer with
geotechnical expertise, or hydrogeologist.
soils
For dry swales placed in subsoils having a
is required; and,
Designs shall verify soil permeably
when an underdrain system is installer
Underdrains
group designation of B, C, or D, an underdrain system
soils testing outline in Section 4. A soil testing is not required
Underdrains shall be included in the design when subsoil infiltration rates are below 1.0 inch/hr;
When an underdrain is required a minimum 6-inch-diameter perforated pipe shall be installed in a trench lined
with filter fabric and filled with a foot depth of clean pea gravel;
o The pipe spacing shall be at a maximum of 10 feet on center and a minimum grade of 0.5% must be
maintained; and,
o A permeable filter fabric or sand layer shall be required between the gravel layer and the planting soil
bed.
• All underdrain systems shall be day lighted to an outfall structure.
Filter Media
• The recommended planting soil media mixture is:
0 85 — 88 % sand. (washed medium sand is sufficient);
0 8 - 12 % fines. (Includes both clay (max 5%) and silt; and,
0 3 -5 % organic matter (leaf compost or peat moss);
• Designs shall use certified media mixed from a vendor that meets the following requirements for phosphorus
contend, cation exchange (CEC), and media filtration:
o The recommend P-index value is between 10-50;
o Soils with CECs exceeding 10 are preferred for pollutant removal; and,
o The medial should have an infiltration rate of 1 to 2 inches per hour;
The minimum filter media depth shall be between 24 to 48 inches; and,
Filter media shall be placed in lifts of 12 to 18 inches.
72
Pretreatment
Pretreatment of runoff entering the dry swale is required to trap coarse sediment particles before they reach the filter bed.
Pretreatment measures shall be designed to evenly spread runoff across the channel bottom width of the dry swale.
• Sheet flow: A grass filter strip with a pea gravel diaphragm or other flow spreader. The required length of the filter
strip depends on the drainage area, imperviousness, and the filter strip slope. Design guidance on filter strips for
pretreatment can be found in Appendix 6C; and,
• Channel flow: A Pretreatment Cell, similar to a forebay, is located at the piped inlets or curb cuts leading to the
dry swale and has a storage volume equivalent to at least 15% of the total WQv. The design shall have a 2:1 length
to width ratio. The cell can be formed by a wooden or stone dam or rock berm.
Design Method Criteria
• Shape: The swale shall have a trapezoidal or parabolic cross section with side slopes of 3:1, 4:1 or flatter. Flatter
slopes are encouraged where space is available;
• Bottom Width: The swale bottom width shall range from 4 to 8 feet;
• Longitudinal Slope: The slope of the swale shall be between 1% and 4%. 1% and 2% are recommended to permit
temporary ponding of the WQv within the channel. The grade should be continuous and uniform;
• Ponding Depth: Drop structures or check dams can be use to create ponding cells along the length of the swale.
The maximum ponding depth in a swale shall not exceed 18" at the most downstream point. The average ponding
depth throughout the swale should be no deeper than 12 inches. The swale ponding area provides for surface
storage of stormwater runoff before it filters through the filter bed. The swale ponding area shall contain the entire
volume associated with the runoff Water Quality Volume of 1.1 Inches;
• Check Dams: Drop structures or check dams shall be space ed on the channel slope and ponding requirement.
Check dams must be firmly anchored into the side -slopes t vent outflanking and be stable during the 10 year
and 100 year storm events. The height of the check dam shoul exceed 18 inches. Armoring may be needed
behind the check dam to prevent erosion, and shall be°design to s read runoff evenly over its surface;
• Drawdown Time: Dry swales shall be designed so that the water quality treatment volume is completely filtered
within 24 hours or less. The drawdown time can be achieved by using a sandy soil mix along with and
underdrain system-'
• Filtering Treatment Criteria: The filtering bed shall have a minimum depth of 24";
o The soil filter bed shall be sized using a Darcy's Law equation with a filter bed drain time of 24 hours
and a coefficient of permeability (k) of 0.5 ft/day; and,
o The required filter bed area (Af) is omputed using Equation 6-6.
• Conveyance and Overflow: Dry swales s all be designed with dimensions and slopes such that a velocity of 3 feet
per second will not be exceeded for the 1.1 inch rain event. The swale shall covey the 10 year and 2 year storm
events at non -erosive velocities with at least 6 inches of freeboard.
Minimum Requirements
• Inlet to dry swales shall include energy dissipaters, such as rip rap;
• Do not use heavy equipment in the dry Swale; and,
• Dry swales can be used for snow storage as long as an overflow is provided and they are planted with salt tolerant,
non -woody plant species. Tree and shrub locations cannot conflict with plowing and piling of snow into storage
areas.
Access and Setbacks
Bioretention systems shall meet the minimum setback requirements specified in Section 7; and,
Provide dedicated maintenance access route to the facility from a public roadway. Access route to be dedicated by
maintenance easement or tract.
Surface Cover and Planting Requirements
• Dry swales system shall have a 3 to 4 -inch landscape layer placed above the filter media to protect the soil bed
from erosion. The landscape layers include the following:
o Turf Grasses: Turf grasses that require minimal maintenance shall be use in dry swales. Native grasses
are preferred, but not required. Salt tolerant grass species should be chosen for dry swale application
along roads. Grasses must be capable of surviving both wet and dry conditions; and,
73
o River Stone or Pea Gravel: Stone or gravel are not recommended in parking lot application since the
increase soil temperatures and have low water holding capacity.
• A dense vegetative cover shall be established over the contributing drainage area before runoff can be accepted
into the facility;
• A landscape plan shall be provided for the dry swale in the drainage report; and,
• It is highly recommended that the planting plan be prepared by a qualified landscape architect.
Maintenance Criteria
• The maintenance access shall be designed such that all areas of the dry swale can be easily accessed, and shall be
designed to allow vehicles to turn around;
• A maintenance right-of-way or easement shall be provided from a driveway, public or private road. The
maintenance access shall have a minimum unobstructed drive appropriately stabilized to withstand maintenance
equipment and vehicles;
• Maintenance for dry swales shall meet the requirements set in Section 10:
• Successful establishments of dry swales requires annual inspections to trigger maintenance;
o Spot Reseeding Inspector should look for bare or eroding areas in the contributing drainage or around
the dry swale area, and make sure that they are immediately stabilized;
o Fertilization: One-time, spot fertilization may be need for initial plantings;
o Remove any accumulated sediment deposits on the filter bed surface or in the pretreatment cells; and,
o Inspect side slopes and grass filter strips for evidence of any rill or gully erosion and repair.
FIGURE 6-8, DRY SWALE DETAILS, NTS
4' TO 8'
AKIN FREEBOARD
410 YEAR LEVEL fiC�l�
2 YEAR LEVEL— .. .
r 7 LEVEL SLOPE OR FLATTER
d y
4 Q4dd dd d4 d4 d 44
d d dd d d dQ d A dd 3 8d d d 4d � d
� daga'�q�ygddadddqdad8da AIIN 2.5�
d6 dd Add ddd dQda44dGCA SOIL E�IA
dd d 4 4d d 8 Cd � 4 nG 4 h aq 46
FILTER FABRIC °
0 0000 00000 0
MIN 1'
6' UNDER DRAIN PEA GRAGEL
PERFORATED PIPE
DRY SWALE CROSS SECTION, NTS
FIGURE 68, DRY SWALE DETAILS, NTS
(CONTINUED)
74
RETREATMENT {FOREBAY) 6" UNDER DRAIN
PERFORATED PIPE
RIPRAP - - - --
OUTFALL PROTECTIO
i
'•iiiTii itV.-• "-UUW.V&iii ifYIaLifLw.W 9LULW i%SILLLLSLi7ii•
" iR ?sRTl�►YlM.7FY�1'liT+n7L�f►R ...... .M1'S7i�►�7r �t �tS7C
OUTFA
. STRIA
K DAIS
DRY SWALE PLAN VIEW, NTS
OUTFALL
RIPRAP
FILTER FABRIC-1/ o
MIN V PEA GRAVEL%%
6.3.9 WETLANDS
ENT (FORERAY)
HECK DAM
UNDER DRAIN
'ERFORATED PIPE
�,,�/12� AVG DEPTH
:a:YwYY:,w�
-- .•.�u1W �2.5'�IL AIEDIk-.:`�'t Q-;•YWbv
°a�*
DRY SWALE LONGITUDINAL SECTION, NTS
NIN FREEBOARD
A wetland analyses is required for all new development and redevelopment. A wetland checklist, located in Appendix 3
A, is required to be completed and submitted with the drainage report. The Wetland checklist helps to identify if wetland
resources may be present and further wetland assessment is required. If you check "yes" for any wetland indicators on the
checklist, a Wetland Assessment outlined in the Kalispell Stormwater Quality Management Plan is required. The
assessment must be performed by a wetland professional trained and familiar with the current US Army Corps of
Engineers Regional Supplements for Wetland Delineations and the most recent Army Corps of Engineers guidance for
Jurisdictional Determinations. Refer to City of Kalispell Stormwater Quality Management Plan for additional details.
In rare instances, wetlands can be used for water quality treatment. Protection strategies in the table below have been
developed to protect wetlands from changes to their hydrology, plant diversity, function and water quality. An on -site
wetland assessment is required to determine the stormwater management classification for each wetland. Refer to
Stormwater Quality Management Plan Chapter 3.4 for the procedure on how to use Table 6.1.
Table 6.1 - Wetland Protection Standards* (Stormwater Oualitv Management Plan)
Stormwater
Bounce Limit
Inundation Period
Water Quality (WQ)
Management
T
2
(2-yr Storm Event)
s
(2-yr Storm Event)
4
Pretreatment
Classification
75
Maintain existing
Maintain existing
Implement WQ standards
Preserve
hydrologic conditions
hydrologic conditions
prior discharge into
(historical if hydrology has
(historical if hydrology has
wetland
recently changed)
recently changed)
Existing hydrologic
Existing hydrologic
Implement WQ standards
Manage 1
conditions plus 0.5 foot
conditions plus 1 day
prior to discharge into
increase allowed
increase allowed
wetland
Existing hydrologic
Existing hydrologic
Implement WQ standards
Manage 2
conditions plus 1 foot
conditions or longer
prior to discharge into
increase allowed
wetland
Sedimentation basin (15 CY
Manage 3
Existing hydrologic
Existing hydrologic
storage volume per
conditions or higher
conditions or longer
impervious acre of
watershed) 5
* Adapted from Minnesota Storm -Water Advisory Group, 1997 & MnBWSR, 2004
1. Management Classification as determined by field inventory and ranking methodology outlined in Appendix A or current version.
2. Height between typical water level and 2-year high water level (HWL).
3. Inundation period begins with the storm event and ends when water levels drop back to within 0.5 feet above the typical water level.
4. Pretreatment of urban runoff before entering wetland
5. Wetland may be used to meet water quality volume (WQ) BMP standards with a sedimentation basin upstream of wetland to collect coarse
sediment or other upstream permitting requirements if more restrictive.
6.3.10 EMERGING TECHNOLOGIES AND MECHANICAL TREATMENT
Emerging technologies and mechanical treatments include but are not limited systems that treat stomwater through
filtration, settling, absorption, adsorption, or a combination of these mechanisms. Mechanical treatment can be used
for retrofits (redevelopment) when all other options I
ve beenxhausted. Mechanical treatment using
hydrodynamic or vortex swirl action can also be used for se entation pretreatment prior to discharging into an
approved treatment BMP. The mechanical treatment device shall°e approved on a case by case basis. The City of
Kalispell will allow mechanical treatment systems based on the Washington Department of Ecology's new
technology evaluation program or equivalent.
The City Engineer reserves the right to den e use of any emerging technologies and mechanical treatment systems
even if it has been approved by Ecology. The ity shall consider the following as they make decisions regarding the
use of new stormwater technologies:
Remember the goal: The goal of any stormwater management program or BMP is to treat and release stormwater in a
manner that does not harm beneficial uses. Treatment performance objectives are listed in the Stormwater Quality
Management Plan.
Exercise reasonable caution: An emerging technology shall not be considered for use for new development
sites unless there are strong supporting data indicating that its performance is expected to be reasonably
equivalent to the BMPs already approved by the City.
Conduct a monitoring program: Identify an acceptable monitoring protocol to apply to those emerging
technologies that have not yet been verified for limited or full-scale use at Ecology's website.
76
APPENDIX 6A
BM T5.100 API (Baffle type) Separator Bay
(Source Section 5.10.7 of the Stormwater Management Manual for Eastern Washington.)
Design Criteriia
The design criteria for small drainages are based on the design velocity,
oil rise rate„ residence time; uYdth, depth„ and length considerations_ As a
correction factor„ the Ammcan Petroleum Institute (API) turbulence
criterion is applied to increase the length.
Ecologv is modifying the API criterion for treating storm ater runoff
from small drainage areas (fueling stations; commercial parking lots„ etc.)
by using the design hydraulic horizontal velocity, Vb, for the design Vt ' V
ratio rather than the API iT11 MIM Of V,V, = 15. The APT criterion
appears applicable for greater than nvo acres of impen�ious drainage area.
Performance verification of this design basis must be obtained during at
least one wet season using the test protocol referenced in Section 5.12 for
neuv technologies.
The follawtag is the sizing procedure using the modified API criterion
Determine the ail rise rate, Vt, in cm sec, using Stoke's Lave ([Water
Pollution Control Federation_ 1985), or empirical determination, or
0.033 ft./min for 603F oil_ The application of Stoke's Lays; to site -based
oil droplet sizes and densities„ or empirical rise rate deterniii Lions
recognizes the need to consider actual site conditions. Iu those cases
the design basis %vould not be the 60 micron droplet size and the 0.033
frimin. rise rate.
Stoke's Lain equation for rise rate; Vt (cucVsec):
V,= g(6--6-)IY )I8Tlw)
Alere: g = gmitational constant (981 cm.'sec'
D = diameter of the oil particle in cm
Use oil particle size diameter D-60 microns (0.006 cm)
g, =0.999 gm�cc_ at 327
u¢: Select conservatively high ail density. for example:
if diesel oil @ as = 0.85 gm-`oc and motor oil @ cF¢ = 0.90 can be
present, then use a¢ = 0.90 z !cc
-qA. = 0.017921 poise. gm�cm-sec at Imo= 327
(See API Publication 421. February; 1990)
• Use the fallowing separator dinxension criteria:
Separator water depth d = between 3 and 8 feet to ininimi ae turbulence
(API„ 1990; US :army. Carps of Engineers, 1994)
Separator width w = benveen b and 20 feet (VVEF & ASCE, 1998;
King County Surface Water Management, 199
77
Depth to width ratio Tw = benveeu 0.3 and 0.5 ( API. 19 90)
For stormwater inflow from drainages less than 2 a€ins:
• Determine' F, and select depth and width of the separator section hased
cm above criteria.
• Calculate the mime tun residence time (to of the separator at depth
(d):
my = TV,
Calculate the horizontal velocity of the hulk fluid, VL, vertical cross -
sectional area, A, and actual design'Vtj%I, (American Petroleum
Institute, MO-1 US Army Carps of Engineers, 1994).
(Vb nuximum at < 2.0 fl:'tuin; American Petroleut Institute, 1990)
Q = 2_15 durs the water quality design flow rate in f''nlin, at
vurumunt residence time, tm
At VhiVtdeternune F, turbulence and short-circuiting factor kppendix
V-D of the SMS1 '104� r1PI F factors rauge from 1.28-1.74.
(American Petroleum Institute, 1990)
• Calculate the minimum length of the separator section 1(s), using:
1(s) = FQt�;'wd = F(Vhh Vad
1(t) = l(f) + I(s) +1(a)
1(t) =1(t 3 + I(s) + 1(t}-'4
Where-
1(t) = total length of 3 baw,
1(f) = length of forebay
1(a) = length of afterbay
• Calculate V=1(s)lxd = FQM and Ah = M(s)
V = nyiniimm hydraulic design volume
Ah = minimum horizontal area of the separator
78
APPENDIX 6B
Flow Spreader Options
Flow spreaders function to uniformly spread flows across the inflow portion of water quality facilities.
• Anchored plate (Option A)
• Concrete sump box (Option B)
• Notched curb spreader (Option C)
• Through -curb ports (Option D)
• Level spreader treanch (Option E)
Options A through C and E can be used for spreading flows that are concentrated. Any one of these options can be used
when spreading is required by the facility design criteria. Options A through C and E can also be used for unconcentrated
flows, and in some cases must be used, such as to correct for moderate grade changes along a filter strip.
Options D is only for flows that are already unconcentrated and enter a filter strip or continuous inflow biofiltration swale.
Anchored plate (Option A)
An anchored plate flow spreader shall be preceded by a sump having a minimum depth of 8 inches and minimum width of 24
inches.
The top surface of the flow spreader plate shall be level, projecting a minimum of 2 inches above the ground surface of the
water quality facility, or v-notched with notches 6 to 10 inches on center and 1 to 6 inches deep (use shallower notches
with closer spacing). Alternative designs are allowed.
A flow spreader plate shall extend horizontally beyond the bottom width o the facility to prevent water from eroding the
side slope. The horizontal extent should be such that the bank is pfotected for aflows up to the 100-year flow or the
maximum flow that will enter the WQ facility.Flow spreadcr plates shall be securely fixed in place.
NP
Flow spreader plates may be made of either wood, metal, fiberglass, reinforce plastic, or other durable material. Anchor posts
shall be 4-inch square concrete, tubular stainless stee or other material resistant to decay.
Concrete sump box (Option B)
The wall of the downstream side of a rectangu one to sump box shall extend a minimum of 2 inches above the treatment
bed. This serves as a weir to spread the flows uni y across the bed.
The downstream wall of a sump box shall have "wing walls" at both ends. Side walls and returns shall be slightly higher than
the weir so that erosion of the side slope is minimized.
Notched curb spreader (Option C)
Concrete for a sump box can be either cast -in -place or precast, but the bottom of the sump shall be reinforced with wire mesh for
cast -in -place sumps. Sump boxes shall be placed over bases that consists of 4 inches of crushed rock, 5/8-inch minus to help
assure the sump remains level.
Notched curb spreader sections shall be made of extruded concrete (or equivalent) laid side by side and level. Typically five
"teeth" per four -foot section provide good spacing. The space between adjacent "teeth" forms a v- notch.
Through -curb ports (Option D)
Unconcentrated flows from paved areas entering continuous inflow biofiltration swales can use curb ports to allow flows to
enter the swale. Curb ports use fabricated openings that allow concrete curbing to be poured or extruded while still providing an
opening through the curb to admit water to the WQ facility.
Openings in the curb shall be at regular intervals but at least every 6 feet (minimum). The width of each curb port opening
shall be a minimum of 11 inches. Approximately 15 percent or more of the curb section length should be in open ports, and no
port should discharge more than about 10 percent of the flow.
Level Spreader Trench -pea gravel (Option E)
The trench shall be a 2' by 2' trench filled with pea gravel.
79
Flow Spreader Caption A: Anchored Plate
v-matched or level
plate spreader
anchor posts
spaced G' D.C.
or at each end
if width < 6
2" min.
Alternative Desi n
Catch basin recommended for
higher flow situations (generally
for iMow velcoMes of 5 fps or
greater for 100 year storm).
PLAN MEW
NTS
SECTION A -A
NTS
orotpction at o0falls
Extend into slope to protect
from the 100 year flaw or
the highest flow entering
water quality facility.
edge of sand
riprap
pond side slope
Ilayer
existing grade
ate hotted to anchor past
2' (min) embedded into existing ground
so
FLOW SPREADER OPTION B: CONCRETE SUMP BOX
Example of a concrete sump flow
spreader used with a biofiItration swale
(may be used with other WO facilities).
concrete sump
outfall riprap pad
inlet pipe
A*
Rack protection at ❑utfall
inlaf nines
Note: Extend sides into slope. Height of
side wall and wing walls mast be sufficient
to handle the 1 00-year flow or the highest
flow entering the facility.
— side with wing walls
see note
/Swale bottom
�B
.a -
wing wall
*B
PLAN VIEW
NTS
wing wall outline
F— Z' min. clearance
concrete sump
{4" wall thickness}
SECTION A -A
NTS
�qp ry2�(min.)
aJ9�9�r JLlOo
SECTION B-B
NTS
__.+A
EM
FLOW SPREADER OPTION C. NOTCHED CURB SPREADER
PLAN VIEW
NTS
1 { I { 1 1 1
1
1
I
± 1 1 Y • • •
7 60-
N
} { I
E
x
inflow
FRONT VIEW A -A
NTS
SECTION E reinforce as necessary
NTS
FLOW SPREADER OPTION D. TRROUGH-CURB PORT
reinforced concrete curb r O•
°t ,opening 11" min.
grass filter strip
CURB PORT
NTS
82
FLOW SPREADER OPTION E: LEVEL SPREADER TRENCH
PLAN VIEW
CURB CUT
RIPRAP INFLOW
(18" DEPTH, CLASS I)
'WIDTH
BIOFILTER--�
t
LEVEL SPHEADER
TRENCH (PEA GRAVEL)
PROFILE VIEW
CURB CUT
RIPRAP INFLOW
(1 S" DEPTH, CLASS 1)
is
2 WIDTH IOFILTER
� II-
LEVEL SPREADER
TRENCH (PEA GRAVEL)
2'DEPTH
DETAIL: TYPICAL PEA GRAVEL
LEVEL SPREADER NTS
ti;
APPENDIX 6C
Filter Strips used for pre-treatment:
Bioretention areas may utilize a filter strip as a pre-treatment measure. The required length of the filter strip depends on the
drainage area, imperviousness, and the filter strip slope. The table below provides sizing guidance for using filter strips for
pre-treatment.
Sizing of Filter Strips for Pre-treatment
Source: Adapted from Georgia Stormwater Management Manual
Parameter
Im ervious Areas'
Pervious Areas (Lawns, etc)'"
Maximum inflow
approach length
35
75
75
100
(feet)
Filter strip slope
(max = 5%)
< 2%
> 2%
< 2%
> 2%
< 2%
> 2%
< 2%
> 2%
Filter strip
minimum length
10
15
20
25
10
12
15
18
(feet)'
1 — 75 feet maximum impervious area flow length to filter strip.
2 — 150 feet maximum pervious area flow length to filter strip
3 — At least 25 feet is required for minimum pre-treatment 0% TSS removal. Fifty feet is required for
50% removal.
Flow must enter the filter strip as sheet flow, desig d to s ad out over the width of the strip with a depth of 1 to 2
inches.
An effective flow spreader is a pea gravel diaphragm at the op of the slope (ASTM D 448 size no. 6, 1/8" to 3/8").
The pea gravel diaphragm (a small trench running along the top of the filter strip) serves two purposes. First, it acts
as a pre-treatment device, settling out se invent particles before they reach the treatment BMP. Second, it acts as a
level spreader, maintaining sheet flo runoff flows over the filter strip. Other types of flow spreaders include a
concrete sill and curb stops.
Grass Channels Used for Pretreatment:
Bioretention areas may utilize a filter strip as a pre-treatment measure. The length of the grass channel depends on the
drainage area, land use, and channel slope. To be used as a pretreatment measure, the grass channel must have a minimum
length of 20 feet. The Table below provides minimum lengths for grass channels based on channel slope and percent
imperviousness (of the contributing drainage area).
Grass Channel Sizing Guidance
(Source: Georgia Stormwater Management Manual)
Parameter
< 33% Impervious
Between 34% and 66%
< 67% Impervious
Impervious
Slope
< 2%
> 2%
< 2%
> 2%
< 2%
> 2%
(max = 4%)
—
—
—
Grass channel min.
length (feet)
25
40
30
45
35
50
assumes 2-ft bottom width
84
SECTION 7 - FLOW CONTROL
7.1 INTRODUCTION
This Section outlines the requirements for sizing flow control facilities. Standard flow control facilities are detention,
retention (natural depressions), and infiltration facility. Any other facility is considered a non-standard system, and shall be
evaluated individually by the City Engineer. Flow control facilities are necessary to mitigate potential adverse impacts on
down -gradient properties due to the increase in stormwater runoff caused by land development.
The peak rate of stormwater runoff from any proposed land development to any natural or constructed point of discharge
downstream shall not exceed the pre -development peak rate of runoff The post development volume of runoff can exceed
the pre -development volume of runoff when the required down -gradient analysis demonstrates that there will be no adverse
impacts on down gradient properties or existing natural and constructed conveyance systems. Refer to Section 10 for
maintenance requirements.
7.2 APPLICABILITY
All projects that meet the regulatory threshold outlined in Section 2, shall comply with this Basic Requirement.
The regulatory threshold or "trigger" for requiring compliance with this Basic Requirements is outlined in Section
2.1.
7.3 DETENTION FACILITIES
A detention system is a storage facility that has a surface disch e. det 'on facility is intended to control peak
stormwater runoff rates but may not control volume.
Underground Facilities
The City of Kalispell has a policy against underground detention structures, due to many observed problems in local
applications and the potential for future problems. Underground detentions structures are not allowed for several
reasons:
• Underground facilities have costly long term maintenance costs. They are hazardous confined spaces and require
yearly maintenance resulting in a higher life cycle cost than the approved BMPs. The City is responsible to see
that BMP maintenance is performed as part of their NPDES permit requirements.
• It is very difficult to inspect underground structures, which are controlled by OSHA safety regulations. A buried
system is easy to neglect resulting in a system that ultimately does little good at protecting the City's water
resources.
• Underground structures may not receive enough air and proper ventilation to avoid anaerobic conditions and
dangerous flow conditions.
• Stormwater runoff quality is not substantially improved or enhanced by underground detention. Underground
faciliteis do not allow grass or other vegetation to absorb nutrient, metals, or pollutants from the stormwater runoff.
7.3.1 MINIMUM REQUIREMENTS
The following minimum requirements shall be met. Additional requirements are specified in Section 7.7.
Discharge Rates
Detention facilities shall be designed such that the release rate does not exceed the pre -developed conditions for various
storm events. The analysis of various design storms is needed to control and attenuate flows from both low and high
frequency storm events.
The total post -developed discharge rate leaving the site shall be limited to the pre -development rates outlined in Table 7-
1. By-pass flow shall be discharged at the pre -developed flow rate. Bypass flow is the runoff that leaves the site without
being conveyed through the new development or redevelopment drainage system.
Table 7-1
Allowable Discharge Rates
Design Frequency (Type 1 -24 hr storm)
Post -Developed Discharge Rate'
2-year (WQr)'
< 50 % of the 2-year pre -developed
10-year
< 10-year pre -developed
100-year (Emergency Overflow)
Overflow route only
1 Post -developed flow is equal to the release from detention facility plus the bypass flow.
2 The emergency overflow shall direct the 100 year post -developed flow safely towards the
downstream conveyance system
3 Water Quality Flow Rate Control Standards
If the detention facility is also proposed to function in conjunction with a water quality treatment facility, the
following criteria must be met:
• The first orifice or outlet from the facility must be a placed a minimum 6 inches above the pond bottom; and,
• Infiltration rate shall be verified by methods outlined in Section 4.
Facility Volume �.
The NRCS Type 124 hour storm events are the design storms be use or all flow control facilities that use a surface
discharge. The design water surface for all facilities shall be the 100 year post developed water surface elevation. All
overflows (structure or spillway) shall be located above th ign ester surface elevation and pass the 100 year -24 hr
post developed peak flow rate.
Setbacks
When a detention facility is proposed upslope of develop roperty or at the top of a slope inclined 15% or greater, the
minimum setback from the slope must be greater th o equal to 50 feet or as determines by a licensed engineer with
geotechnical experience. The distance between the outlet structure and the inlet into the detention facility shall be
maximized.
Release Point
Stormwater runoff from a developed site shall leave the site in the same manner and location as it did in the pre -developed
condition. Therefore, a detention system may be used only when a well-defined drainage conveyance system is
present prior to development.
FIGURE 7-1, TYPICAL DETENTION POND OUTLET SECTION
NTS
CONTROL STRUCTURE
2' MI
EMERGENCY OVERFLOW WS y
POND OVERFLOW WS y inn YR P4—HR
POND DESIGN WS Q 1n YR 24—HP
MIN. 6" ,r
SEDIMENT STORAGE
EMBANKMENT
iTOP WIDTH OF BERM
EMERGENCY]
OVERFLOW SPILLWAY
EMERGENCY OVERFLOW SPILLWAY
CROSS SECTION
NTS
TOP WIDTH OF
EMERGENCY OVERFLOW WS
POND OVERFLOW WS v 100 YR 24—HR =
----------
POND DESIGN WS v 10 YR 24—HR 1 OCK LINING
OMPACTED EMBANKMENT
EMERGENCY OVERFLOW SPILLWAY
CROSS SECTION
NTS
EMERGENCY OVERFLOW WATER SURFACE
� 1 2' MIN.
POND OVERFLOW WS v 100 YR_
1' WELL GRADED ROCK LINING ARMOR
ARMOR WITH COVER, NTS
w �
v 100 YR 24—HR w w i www —
_ " GRASS AND TOP SOIL
I. 11' WELL GRADED ROCK LINING
NOTES: THE ARMORING MAY HAVE A 4" "
COVER OF TOPSOIL AND GRASS
7.4 OUTFLOW CONTROL STRUCTURES
Control structures are manholes or catch basins with a restrictor device used for controlling outflow from a facility to
meet a desired standard. Outflow structures are required for all stormwater detention facilities. The restrictor device is
usually multiple orifices, consisting of two or more orifices and/or a weir section sized to meet performance requirements.
This section presents a general overview of flow control structures.
Runoff shall enter the detention facility through a conveyance system separate from the control and outflow conveyance
system. The distance between the inlet and outlet shall be maximized to reduce sediment from accumulating in the outflow
structure.
7.4.1 OUTFLOW CONTROL STRUCTURE TYPES
Multiple Orifice Restrictors
• In most cases, a control structure needs only two orifices: one at the bottom and one near the top of the riser;
• Minimum orifice diameter is 3 inches; and,
• Orifice shall be constructed on a tee section or on a baffle as in Figures 7.2 to 7.3.
Risers and Weir Restrictor
• Properly designed weirs maybe used as flow restrictors. However they must be designed to provide for primary
overflow of the developed 100 year peak flow discharging to the detention facility; and,
• The combined orifice and riser (or weir) overflow may be used to meet flow requirements. However the design
must still provide for primary overflow of the developed 100 year peak assuming all orifices are plugged.
Skimmer
• A skimmer is used as a flow restrictor and traps floatable debris petroleum product. A skimmer keeps the
outlet pipe free of debris and reduces maintenance; 14
• Provide skimming up to the 10 year event high water level or greater; and,
• Design flow velocities thru the submerged skimmer opening'Fat 1.5 fps or lower under the 10-year event high
water level. See Figure 7.4 and 7.5 for detai `
7.4.2 MINIMUM REQUIREMENTS
The following minimum requirements shall be met. Additional requirements are specified in Section 7.7.
Access Requirements
• An access road to the control structure is required for inspection and maintenance, and shall be designed and
constructed as specified in Section 10; and,
• Manhole and catch basin lids for control structure shall be locking and rim elevation shall match proposed finish
grade.
'-
Figure 7.2 Flow Restrictor Baftle
Frames, grates and round
solid covers marked "drain"
attach shear gate
with locking bolts.
control rod to support
bracket on inside of
1' min. t' in t
frame/grate a evation
_,
_
access opening
under pavement mra.T
per plans
HH
max w.s. p 6-
DESIGN W.S.
6" min.
overflow
I—
Ci
conditions
elbow restrictors—F)
see detail below
_A
shear gate with
handholds,
—11
control rod for drain
steps or ladder
ii
i�
flow
—A
�i
--q
orifice plate 10 gage
2+ min.
�_
f
minimum galvanized
1-4
i`_
steel with orifice
—_
y
diameter 1" minimum
2 -(r min.
ii
less than diameter of
concrete hole
A
t-
removable
water -tight
coupling
SECTION A -A
NTS
PLAN VIEW
NTS
grouted
T
plate welded
to elbow with 6"max•
orifice as
specified
ELBOW RESTRICTOR DETAIL
NTS
SECTION B-B
NTS
Notes:
Metal parts: corrosinon resistant steel parts
galvanized and asphalt coated
Catch basin: 72" diameter, in accordance with
AASHTO M-199
Orifice: sized and located as required with
lowest orifice a minimum of 2' from base
89
removable watertight
coupling or flange
Figure 7.3 Flow Restrictor (Tee)
M
I I'min, under
6" min. pavement 1e"
I
plate welded to elbow— I �---
with orifice as specified elbow restrictor,see detail
pipe supports
ELBOW RESTRICTOR DETAIL see Note 6
NTS 4.5 X a
T min.
D 1 outlet pipe f
y ; see notes 1 & 5
q%�
invert and elevation
per plans
1' section of pipe
attached by gasketed
band to allow removal
restaplate
P�v with orifice diameter as
specified (not needed if
ISOMETRIC for spill control only)
NTS
Notes:
I. Metal parts: corrosinon resistant. Non
galvanized part preferred. Parts
galvanized to have asphalt coated
2. Catch basin: minimum 54" diameter
3. Frame and ladder or steps offset so:
A) Cleanout gate is visible from top,
B) Climb -down space is clear of riser
and cleanout gate
4. If metal outlet pipe connects to cement
concrete pipe: outlet pip to have
smooth O.D. equal to concrete pip I.D.
less 1/4".
5. Provide at least one 3" X .90 gage
support bracket anchored to concrete
wall. (maximum 3 ft vertical spacing)
6. Locate elbow restrictor (s) as
necessary to provide minimum
clearance as shown.
frame, grate & solid cover
marked "DRAIN" with locking bolts
vertical bar
grate for
i� secondary inlet
handholds. steps or
ladder
—2' min
Phear
gate with control
12" rod for cleanout/drain
N
c 12" (rod bent as required
for vertical alignment
with cover)
12" ,
SECTION A -A
NTS
2' min. clearance
to any portion of frop-T
including elbows
�ItI
angle as
(necessary
see note 7
elbow restrictor 2' min.
see detail
PLAN VIEW
NTS
11
A
ladder rungs
111
2"x6" KEYWAY -
CAST INTO WALL
BY SUPPLIER
BAFFLE WALL--,
MUST BE
POURED IN
PLACE
XX" DIA. HOLE -
IN BAFFLE WALL
RECTANGULAR --
SKIMMER
OPENING
FOR GRATE DESIGN
SEE DETAIL
Figure 7.4 Skimmer (with baffle wall)
HOLE FO
XX" RCP
SKIMMER
GRATE
SKIMMER
DIAMETER
SKIMMER
OPENING (WxH)
3'
2'x0.5'
4'
3'x1'
5'
4'x1'
6'
5.5'x1.5'
0 HOLE CENTERED
3AFFLE WALL
ITIONAL #4'S
-0" LONG
9 12"
IZONTAL
® 12"
VERTICAL
SECTION A -A
CONCRETE BAFFLE WALL
XX" DIA. HOLE IN
BAFFLE WALL
RIM ELEV. XXXX'
-
- -
HOLE FOR XX" DIA.
ELEV.= XXXX
OUTLET PIPE
ET (OE)
0.
EO
LEV XXXX
0.5'
L
4'(W) X 1'(H)
-
1
MIN. OPENING
1'
4 CY CLASS O
1" MENUS AGGREGATE
1 RIPRAP 0 6'
5' DIA.
(MIN.)
NOTES:
1. SEE STORM DRAWINGS/SCHEDULE FOR DESIGN
ELEVATIONS.
2. CENTER SKIMMER ON O.E. CONTOUR AND GRADE IN
FRONT OF SKIMMER OPENING AS NECESSARY TO
PROVIDE FOR SKIMMER OPENING.
3. ANCHOR BOLTS SHALL BE STAINLESS STEEL (OR HOT
DIPPED QALVANIZED) WEDGE OR STRIKE ANCHORS, 3.5"
MIN. LENGTH.
4. PREFABRICATED GALVANIZED SKIMMER GRATE, PLATE
STYLE BY HAALA INDUSTRIES IS AN APPROVED EQUAL.
(SEE HAALAINDUSTRIES.COM)
STANDARD DETAILS
PONDING BASIN SKIMMER STRUCTURE
WITH CONCRETE BAFFLE WALL
91
Figure 7.5 Skimmer
1/2 ANCHOR
CLIPS (1)
1/2"x3/8" OUTER RING
1/2"x3/8" STEEL
qRS AT 4" O.C.
1-1/4"
/4"x 1 /4"
EEL BAR WELD
) EACH MEMBER
OT-DIPPED GALVANIZED
RATE IN 2 SECTIONS (2)
OPENINGvy1\
(I)AIE OF__Al�
RIM ELFV. XXXX'
OUTLET ELEV. (OE)
ELEV= XXXX'
SKIMMER
OPENING
0.5'
4 CY CLASS 00
1 RIPRAP 0 66
C)
T]
HH
t tD,
DIA. VARIES
NOTES:
1. SEE STORM DRAWINGS/SCHEDULE FOR DESIGN
ELEVATIONS.
2. CENTER SKIMMER ON O.E. CONTOUR AND GRADE IN
FRONT OF SKIMMER OPENING AS NECESSARY TO
PROVIDE FOR SKIMMER OPENING.
3. ANCHOR BOLTS SHALL BE STAINLESS STEEL (OR HOT
DIPPED QALVANIZED) WEDGE OR STRIKE ANCHORS, 3.5"
MIN. LENGTH.
4. PREFABRICATED GALVANIZED SKIMMER GRATE, PLATE
STYLE BY HAALA INDUSTRIES IS AN APPROVED EQUAL.
(SEE HAALAINDUSTRIES.COM)
SKIMMER
DIAMETER
SKIMMER
OPENING (WxH)
3'
2'xO.5'
4'
3'xt'
5'
4'x1'
6'
5.5,x1.5,
HOLE FOR XX" DIA. OUTLET
PIPE
STANDARD DETAILS
PONDING BASIN SKIMMER STRUCTURE
1" MINUS AGGREGATE
BACKFILL
92
Methods of Analysis
Table 7-2 provides equations and coefficients for calculating flow through the most common types of weirs and orifices
used for flow control. For additional information on weirs the engineer should consult a hydraulic reference.
TABLE 7-2
FLOW EQUATIONS FOR I _ MOi S NN IR AND ORIFICE Ti-PES
Weir?Orifice Type
Equation
C
Sharp Crested 17-notch
%Veirl
Broad Crested Suppressed
_ CLHX
033
Rectangular ,.vein
RectangWar Sharp Crested
Weirs':
= C(L — 02.I-J-)H
3.27 + OAD
Contracted
Y
Suppressed
_ZH
Sharp Crested Cipoletti
{Trapezoidal)-
Q = CLH
3.367
Side slopes are 1:4
Broad Crested Irapezaidal
Q _ 2 )U2
I-3IB L+ (Y-an.9)H
D_60
15
Orifice
Q = C4 2F.H-
0_62
The weir inverts should be set above the pond battoma a height of at least tgrice the maximum head_
Q = flow (cfs); C = coefficient of discharge; 3 = area of ozifice (square feet); H= hydraulic head (feet);
g = grati itv (32.2 feet'3econd2); d9 = auele of side slopes (degrees); Y= storage depth (feet); Z = weir length
or opening (feet)
Risers Overflow
Figure 7-7 can be used to determine the headPFr
t) above a riser of given diameter and for a given flow (usually the
100-year peak flow for developed conditions)ditional information, consult a hydraulics reference.
93
100
0
to
7 .., 2 ............ 5 4 '48
33
30
27
24
F
A
0.1 HEAD IN FEET (measu 1 red from crest of riser) 10
Q,,.ir=9.739 D H312
Q.,jjj..=3.782 D 2 H 1/2
Q. in cfs, D and H in feet
Slope change occurs at weir -orifice transition
Figure 7-7 — Flow Rates vs. Head (riser)
94
7.5 INFILTRATION FACILITIES
An infiltration facility is used for disposing of stormwater runoff into the subsurface and can be used for flow control
provided that:
• The discharge is uncontaminated or properly treated prior to the stormwater entering the infiltration facility;
• The Geotechnical Site Characterization demonstrates the suitability of the soil for subsurface disposal; and,
• The down -gradient analysis indicates that adverse impacts are not anticipated.
The engineer shall consider the impact of infiltration on groundwater elevations both on site and on down -gradient
properties.
7.5.1 MINIMUM REQUIREMENTS
In addition to the requirements specified in Section 7.7, infiltration facilities shall meet the minimum requirements
described below.
Pretreatment
Pretreatment is required for urban watersheds with more than 0.25 acres of impervious surface before the
stormwater enters the infiltration facility;
• Pretreatment volume shall be equal to 20% of WQv. The pretreatment volume is in addition to the
infiltration basin's WQv sizing requirement.
Depth to Groundwater and Limiting Layer
• The base of the infiltration facility shall be > 5 feet ab<thiting layer (bedrock, clay lens, etc.); and,
• The bottom of the basins should be a least 3 feet absonal high groundwater table.
o The seasonal high water table wone n long-term piezometer records during at
least one wet season or the mottler as determined by a licensed geologist,
licensed engineer with geotechnicse, or hydrogeologist.
Access and Setbacks
Minimum infiltration facility setback restriction .
o Building Foundatio Infiltration facility to be at least 50 feet up -slope and 20 feet down -slope
from building founda ess a reduction is geotechnically justified;
o Back from top of slop eater than 15%: At least 50 feet or as determined by a licensed
engineer with geotechmcal expertise;
o At least 200 feet from springs used for drinking water supplies;
o Septic drain fields: At least 100 feet;
o Shallow water supply wells (typically individual homeowner wells): At least 100 feet;
o Easement, external tracts or property line: 20 feet; and ,
o Floodplain: Outside 10-year High Water Level (HWL).
Provide dedicated maintenance access route to infiltration facility from a public roadway. Access route to be
dedicated by maintenance easement or drainage parcel.
Infiltration Criteria
• Short term infiltration rates shall be determined using the field methods presented in Section 4;
• The short-term soil infiltration rate should be a minimum of 0.5 inches/hr and a maximum of 2.5 inches/hr;
• Infiltration facility drawdown time: Designed to drain dry within 72 hours after storm flow to it has
stopped:
o Infiltration basins will need to be refreshed and infiltration rate restored when the actual draw
down time to drain dry exceeds 72 hours.
• Long-term soil infiltration rate determination: The long-term infiltration rate is the estimated short-term rate with
an applied reduction factor and shall be used for the design. The reduction factor is to account for measurement
uncertainty, site variability, fluctuation of infiltration rate with water levels, pretreatment for total suspended solids
(TSS) control and degree of maintenance that together affect long-term infiltration rates:
o Short-term infiltration rate determination: On site field infiltration tests provide the most
realistic, accurate estimate of percolation rates. The procedure to conduct a pilot test or the
95
small-scale double ring infiltrometer test (ASTM D3385) is described in Section 4:
Reduction factors: The reduction factor is applied to the measured short-term rate. Refer
to Chapter 7 in the Stormwater Quality Management Plan for detailed description or
Appendix 6A; and,
Long-term infiltration rate determination: Divide short-term rate by total reduction factor (RF) to
determine the design long-term infiltration rate.
Planting Requirements
• Plant basin with native vegetation containing a mixture of species of varying moisture tolerances. See Section 7 for
planting guidelines.
Post Construction Verification
• Submit post -construction verification of volume and infiltration capacity:
o Submit an as -built grading plan of the infiltration basin after construction to the City to verify the
design storage volume has been provided; and,
o Perform post -construction testing of actual short-term infiltration rates to ensure the basin
functions as designed or corrective action will need to be taken. Refer to Appendix 4A Pond
Flood Test.
Facility Volume
The size of the infiltration facility can be determined by routing methods outlined in Section 5.4. Infiltration facilities
shall be sized to fully infiltrate the post -development NRCS Type 1 10 year 24 hr design storm and the design water
surface for all facilities shall be the post developed 100 year waters e elevation. All overflows (structure or spillway)
shall pass the 100 year -24 hr developed peak flow rate.
To prevent the onset of anaerobic condition and mosquito biV, th nfiltration facility shall be designed to drain
completely within 72 hours after the design storm event
Location
• If the site has the potential for contaminated or unstal5le soil, then these conditions shall be investigated and
appropriate mitigating measures taken before designing infiltration facilities in theses areas.
a
Figure 7-8Infiltration Facility
p000cL owsx
AS � __IR_�`` /���—�
_________�__________ U_________
SETTLING POND
IF REQUIRED
CONNECTING SPILLWAY-__.
oowrmoL S,pvorvns
INFILTRATION POND
MERGENCY OVERFLOW SPILLWAY
A��� --
PLAN VIEW —
NTS
4'»w6' OR EXISTING
SECTION A —A
NTS
NDETAIL OTES o^SCHEMATIC poPRsSEwvmow ONLY. ^cm^
cowncmnwmw WILL VARY DEPENDING ON SPECIFIC SITECONSTRAINTS AND APPLICABLE DESIGN CRITERIA.
97
7.6 RETENTION FACILITIES
Retention facilities are used for storage of stormwater runoff when site conditions are not conducive to infiltration, and can
be used for flow control provided that:
• The stormwater discharge is properly treated prior to the entering the facility; and,
• Retention facilities shall be sized for storage of the post -developed NCRS Type 1 100 year 24 hour storm event.
7.6.1 MINIMUM REQUIREMENTS
Retention facilities shall meet all requirement outlined for detention facilities and the additional requirements specified
in Section 7.7.
7.7 ADDITIONAL REQUIREMENTS FOR ALL FACILITIES
The following minimum requirements shall be met for all flow control facilities:
7.7.1 GENERAL
The design of flow control facilities shall adhere to the following:
• Pond bottoms shall be located a minimum of 0.5 feet below the outlet to provide sediment storage. Sediment storage
volume shall not be included in the design volume; and,
• In general, all pond bottoms shall be sloped from 0.5% to 1%. Roadside swales are considered flat if the swale
bottom slope is 1% or less. When calculating treatment volume, the designer can assume a flat bottom for
swale/pond bottom slopes up to 1%.
Drainage facilities shall be located within a drainage parcel. Refe cc 0 for specific information.
7.7.2 SETBACKS
• Setbacks for any detention pond, swale or dit mea re rom the maximum design operating depth) shall be at
least 30 feet when located up -gradient or 20 � e hen ocated down -gradient from septic tanks or drain fields.
• Pond overflow structures shall be locat d a min um of 10 feet from any structure or property line. The toe of the
berm or top of bank shall be a mini of 5 fee rom any structure or property line.
• Building Foundation: At least 50 feet the to of the facility's slope;
• Easement or property line: 20 feet from the top of the facility's slope;
• Floodplain: Outside 10-year High Water Level (HWL); and,
• Drainage facilities located at, or adjacent to, schools, nursing homes, day -cares, or similar facilities: At least 200
feet.
7.7.3 DRAWDOWN TIME
Detention and infiltration facilities shall have a minimum subgrade infiltration rate of
0.5 inches/hour and drain completely within 72 hours after a storm event. A drawdown time of 72 hours is intended to
prevent the onset of anaerobic condition and mosquito breeding.
7.7.4 SIDE SLOPES
Pond side slopes shall meet one of the following requirements:
• Interior side slopes shall not be steeper than 4H:IV;
• Pond walls may be vertical retaining walls, provided that:
o A fence is provided along the top of the wall for walls 2.5 feet or taller;
o An 8-foot-wide access ramp to the pond bottom is provided, with slopes less than 4:1 (horizontal to
vertical); and,
o The design is by a professional engineer with structural expertise if the wall is 4 feet or more
in height.
7.7.5 EMERGENCY OVERFLOW SPILLWAY
An emergency overflow spillway shall be provided to bypass the 100-year developed peak flow toward the downstream
conveyance system in the event of plugged orifices or high flows that exceeds the design storm.
Emergency overflow spillways shall be analyzed as broad crested trapezoidal weirs and comply with the following
requirements:
• The spillway shall have the capacity to pass the 100 year -developed peak flow;
• The full width of the spillway shall be armored with riprap and extend downstream to where emergency
overflows enter the conveyance system. The armoring may have a 4" topsoil and grass cover;
• Rip rap shall extend just beyond the point that bank and stream bed erosion occurs:
• If the detention/infiltration facility is located on an embankment, the overflow spillway shall be armored to a
minimum of 10 feet beyond the toe of the embankment; and;
• The overflow path shall be identified on the construction plans and easements shall be provided as necessary.
Engineers may choose to design the detention pond multi -stage outflow structure with an emergency bypass that can route
the 100-year storm through the structure and out of the pond directly into the conveyance channel. However, due to the
high potential for sedimentation and plugged orifices within these structures, an emergency overflow spillway shall
still be provided in order to reduce the potential for a pond berm breach for detention ponds that require an emergency
overflow spillway.
7.7.6 EMBANKMENTS
The height of an embankment is measured from the top of the berm tote catch point of the native soil at the lowest
elevation. Embankments shall meet the following minimum requirements:
• Embankments 4 feet or more in height shall be constpcte as recommended by a geotechnical engineer.
Depending upon the site, geotechnical recommendations y be necessary for lesser embankment heights;
• Embankments shall be constructed on native consolidated soil, free of loose surface soil materials, fill, roots,
and other organic debris or as recommended by the geotechnical engineer;
• Energy dissipation and erosion control shalM provided to stabilize the berm and its overflow;
• The embankment compaction shall produce a dense, low permeability engineered fill that can tolerate post -
construction settlements with minimal cracking. The embankment fill shall be placed on a stable subgrade,
placed in 6" lifts, and compacted to a minimum of 95% of the Modified Proctor Density (ASTM Procedure
D1557);
• Anti -seepage filter -drain diaphragms sh 1 be considered on all outflow pipes and are required on outflow pipes
when design water depths are 8 feet or greater;
• In the event of a berm fracture or failure, the berm shall allow the passage of water through the berm without
additional erosion or failure of the berm structure.
• Embankments must be constructed by excavating a key. The key width shall equal 50 percent of the berm base
width, and the key depth shall equal 50 percent of the berm height; and,
• The berm top width shall be a minimum of 4 feet.
7.7.7 FENCING
Fencing or other barriers may be required to protect the health, welfare and safety of the public. In general, fencing is
required for the following:
• Drainage facilities with the first overflow at 4 or more feet above the pond bottom;
• Drainage facilities with retaining walls 2.5 feet high or taller;
• Drainage facilities located at, or adjacent to, schools, nursing homes, day -cares, or similar facilities;
• Fencing is not required for a typical infiltration swale. However, the City Engineer reserves the authority to
require a fence along any swale or pond should there be a concern for safety; and,
• At the discretion of the City Engineer, if a pond is proposed as an amenity (i.e. enhancements to the disposal
facility are proposed, such as rocks, boulders, waterfalls, fountains, creative landscaping or plant materials), the
design will be reviewed on a case -by -case basis, such that the fencing requirements may be reduced or waived.
At the discretion of the City Engineer, marking fences, terraces, shallower side- slopes, egress bars, etc. may be allowed
instead of fencing.
The minimum fencing requirements are as follows:
• The fencing shall be at least 4 feet tall unless otherwise specified by the City Engineer, and provide visual
access; and,
• Gates are to be provided where drainage facilities are fenced. The gates shall be a minimum of 12 feet wide
with two leaves and have locks.
The City Engineer reserves the authority to waive any and all fencing in commercial areas, as reviewed and accepted on a
case -by -case basis by the City Engineer.
7.7.8 PLANTING REQUIREMENTS
Exposed earth on the pond bottom and interior side slopes shall be sodded, seeded, or vegetated in a timely manner, taking into
account the current season. Unless a dryland grass or other drought tolerant plant material is proposed, irrigation shall be
provided. All remaining areas of the tract or easement shall be sodded or planted with dryland grass or landscaped. Refer
to Appendix 7A for planting guidelines.
7.7.9 LANDSCAPING
Where space and circumstances allow, the landscaping scheme and common use areas shall be integrated with the
open drainage features and into the overall stormwater plan. Plants other than turf grass have characteristics that can
provide additional stormwater management benefits such as enhanced evobtranspiration and improved soil -holding
capabilities.
However, in all cases the landscaping and other uses must /subseNiet tothe primary stormwater needs and functions.
Landscaping shall not conflict with the collection, conveyan treatment, storage, and disposal of stormwater. The following
general principles should guide the landscaping and selectio ants in conjunction with stormwater facilities:
• Supplemental landscaping areas should be grouped into irregular islands and borders outside of the immediate
stormwater facilities and not uniformly dispersed throughout them. The constructed stormwater features should
be irregular and curved in shape to look`"more natural. Avoid straight lines and regular shapes where possible;
• Trees and shrubs shall not be planted on pond liners due to potential leakage from root penetration;
• Planting is restricted on berms that impound water either permanently or temporarily during storms;
• Trees and shrubs shall not be planted within 10 feet of drainage appurtenances such as outlet control structures,
manholes, catch basins, inlets and outlets, spillways, storm drain lines, and underground disposal structures
such as drywells or drain -fields. The minimum spacing between the tree or shrub and the drainage structure
shall be equal to the crown diameter of the mature plant;
• Trees and shrubs shall not be planted within the treatment, storage, and conveyance zones of swales, ponds,
and open channels, unless treatment and storage calculations take into account the mature tree size and allow
runoff to reach the drainage facilities;
• Self-limiting plants shall be used, not spreading or self -seeding types;
• Full-size forest trees and trees with aggressive root systems should not be used except where space and
circumstances allow. Deciduous trees with heavy shade and leaf -fall should also be avoided to allow the
survival of the surrounding grass areas and not plug drainage facilities. Evergreens and smaller ornamental
trees are normally better suited to urban conditions;
• Shrubs should be upright in form and groundcovers should have neat growth patterns to assist in their
maintenance and that of the surrounding grass areas; and,
• The plant selection needs to consider the native soil conditions and altered moisture conditions created by the
stormwater facilities. The plants need to be adaptable to the changes in site conditions. Plants that are self-
sufficient and self-limiting do not require year-round irrigation and require minimal care are encouraged.
Guidelines for plantings are listed in appendix 7A.
7.7.10 MAINTENANCE
Maintenance is of primary importance for drainage facilities to operate as designed. The requirements of Section 10 shall
be met as applicable.
100
7.8 SPECIAL REQUIREMENTS
7.8.1 FLOODPLAINS
Floodplain requirements are administered by the City Planning Department. Contact the City Flood Plain Administrator for
more information and specific requirements.
When any property is developed in or around identified Special Flood Hazard Areas all work must conform to the
requirements of the City of Kalispell Flood Plain Management Ordinance.
7.8.2 WETLANDS
A wetland analyses is required for all new development and redevelopment. A wetland checklist, located in Appendix 3
A, is required to be completed and submitted with the drainage report. The Wetland checklist helps to identify if wetland
resources may be present and further wetland assessment is required. If you check "yes" for any wetland indicators on the
checklist, a Wetland Assessment outlined in the Kalispell Stormwater Quality Management Plan is required. The
assessment must be performed by a wetland professional trained and familiar with the current US Army Corps of
Engineers Regional Supplements for Wetland Delineations and the most recent Army Corps of Engineers guidance for
Jurisdictional Determinations.
Protection strategies have been developed to protect wetlands from changes to their hydrology, plant diversity, function and
water quality. An on -site wetland assessment is required to determine the stormwater management classification for each
wetland. Refer to Stormwater Quality Management Plan Chapter 3.4 the procedure.
The protection standards and classifications acknowledge that w ds onstrate varying susceptibility to stormwater
impacts. The standards for the closest downstream wetland w U ess the wetland discharges into a lake, flow
control standards shall apply to discharges leaving the overfill site.
7.8.3 CLOSED DEPRESSION
Closed depressions are natural low areas that hold a fixed volume of surface water. Depending upon soil characteristics, a
closed depression may or may not accumulate surface water during wet periods of the year. Some closed depressions
may be classified as wetlands. If so, the engineer shall comply with the wetland criteria specified in this section.
Analysis of closed depressions shall include the following at a minimum:
• Identification of the location of the closed depression on the pre -developed basin map;
• A routing analysis of the drainage basins contributing to the closed depression to estimate the peak flow rates
and volumes entering the closed depression in the pre -developed condition;
• An estimation of the storage capacity of the closed depression for the 100- year storm event;
• If the closed depression will be filled in, a facility shall be provided that has the capacity to store the 100-year 24-
hour volume that was historically intercepted by the closed depression. This is in addition to the drainage facilities
required for flow control and treatment due to the increase in stormwater runoff. The construction plans shall
include a grading plan of any closed depression areas to be filled in. The grading plan shall show both existing and
finish grade contours. The plans shall also specify compaction and fill material requirements; and,
• Closed depressions have the same flow control requirement as retention facilities.
7.9 REGIONAL DETENTION PONDS
Regional Detention Ponds are located along major stormwater conveyances and natural drainage ways. Most regional
facilities serve more than a single development within a given contributing drainage basin. Regional facilities have the
potential to lessen flooding in existing drainage problem areas.
The City of Kalispell has adopted the 2008 Stormwater Facility Plan Update with proposed locations for regional
stormwater facilities and mapped natural drainage areas within the study area. The updated plan provides design data for 60
drainage basins including basin delineates, drainage area, and existing natural drainage ways. A quantitative analysis provides
approximate pond storage volumes, allowable peak discharge flow rates and potential regional pond locations.
101
Project owners shall coordinate with the City Staff early in the planning process when the project site is in an area for
which natural drainage ways and regional detention ponds are featured in the 2008 Stormwater Facility Plan Update.
102
APPENDIX 7A
Planting Guidelines
Planting Guidelines for:
Detention Pond: Seed mixtures
Common & Species Name
Bulk
Rate
(lb/ac)
% of Mix
Component
Bluebunch Wheatgrass -
Psuedoroegneria spicata (Goldar)
s
32
Thickspike Wheatgrass —
Elymus lanceolatus (Critana)
5
20
Rough Fescue
Festuca scabrella
3
12
Idaho Fescue
Festuca idahoensis (Joseph)
6
24
Prairie Junegrass
Koeleria macrantha (crastad)
3
12
Grass Totals:
25
100
Or
Slender Wheatgrass
Elymus trachycaulus (Revenue)
4
10
Mountain Brome
Bromus marginatis (Bromar)
6
15
Annual Ryegrass
Lolium multiflorum
6
15
Winter Wheat*
24
60
Cover Crop Totals:
40
100
GRAND TOTAL:
65
100
103
Planting Guidelines for:
Infiltration facilities, Detention facilities, Sivales, and Ditches
Common & Species Name
% of Mix
Component
Perinnial Rye Grass
15
Intermediate Wheatgrass
46
Creeping Fescue
8
Tall Fescue
31
Total 100
Or
Common & Species Name % of Mix
Component
Tall or Meadow Fescue
68
Seaside/ Creeping Bentgrass
10
Meadow Foxtail
10
Alsike Clover
6
Redtop Bentgrass
6
Total
100
Planting Guidelines for Wetponds: Wetland Grasses
Common & Species Name
% of Mix
Component
Redtop Bentgrass
35
Meadow Foxtail
35
Russian Wildrye
20
Red Fescue
7
Bridsfoot Trefoil
2
Blackeyed Susan
1
Total 100
Or
Common & Species Name % of Mix
Component
Redtop Bentgrass
35
Red Fescue
35
Meadow Foxtail
30
Total
100
104
Emergent Wetland Plant Species Recommend for Wetponds
Appendix 7A Planting Guidelines
Upland Sites
Agropyron riparian
Elymus trachycaulus
Elymus lanceolatus
Festuca idahoensis
Moist to Wet Sites
Elymus glaucus
Elymus trachycaulus
Leymus triticoides
Pascopyrum smithii
Emergent Species
(inundated but dry out)
Carex utriculata/rostrata
Carex nebrascensis
Carex lanuginosa
Eleocharis palustris
Juncus balticus
Juncus tennis
Scirpus actus
Inundated locations
Bechmania syzigachne
Carex aquatilis
Carex utriculata/rostrata
Eleocharis palustris
Glyceria striata
Juncus ensifolius
Juncus mertensiana
Juncus tennis
Sagittaria latifolia
Scirpus microcarpus
Scirpus americanus
Scirpus acutus
Typha latifolia
Common Name
streambank wheatgrass
slender wheatgrass
thickspike wheatgrass
Idaho fescue
Common Name
blue wildrye
slender wheatgrass
creeping /beardless wildrye
western wheatgrass
Common Name
beaked sedge
nebraska sedge
wooly sedge
creeping spiked rush
baltic rus
slender ru
hard s me
Common Name
western slough grass
water sedge
beaked sedge
creeping spiked rush
fowl mannagrass
3 stamen/dagger leaf rush
Merten's rush
slender rush
arrowhead
small fruited bulrush
olney's bulrush
hardstem bulrush
cattail
Pounds PLS per Acre
(pure stand) % by weight
5 30
6 20
6 30
3 20
6 30
6 20
6 30
8 20
105
shrubs Common Name
Willows- with standing long inundation
Salix dummondii Drummond willow
Salix boothii Booth's willow
Willows -requires longer dry period
Salix exigua sandbar/coyote willow
Salix bebbiana Bebb's willow
Salix geyeriana Geyer's willow
Moist upland shrubs -see also recommended species list from Native Plant Socie
Acer glabrum
rocky mountain maple
Amelanchier alnifolia
serviceberry
Cornus stolonifer
red osier dogwood
Eleagnus commutata
silverberry
Prunus virginiana
chokecherry
Ribes aurem
golden current
Sambucus racemosa
elderberry
Moist to wet forbs
Iris missouriensis
Mimulus lewisii
Roc
re(
Notes: Regional Disturbers for wetland
West, 4) Western Native Seeds, 5)Wind
s, 2) Blackfoot Native Plants, 3) Native
106
SECTION 8 - NATU RAL AN D
CONSTRUCTED CONVEYANCE SYSTEMS
8.1 INTRODUCTION
A conveyance system includes all natural or constructed components of a storm drain system that collects stormwater runoff
and conveys it away from structures, minimizing the potential for flooding and erosion.
Conveyance facilities consist of curbs and gutters, inlets, storm drains, catch basins, channels, ditches, pipes, and
culverts. The placement and hydraulic capacities of storm drain structures and conveyance systems shall consider the
potential for damage to adjacent properties and contain flooding within traveled roadways. The conveyance system shall
also provide discharge capacity sufficient to convey the design flow at velocities that are self-cleaning without being
destructive to the conveyance facilities. These objectives are achieved by designing all conveyance facilities using the
design storm event specified for the given facility and by adhering to requirements such as minimum velocity, freeboard,
cover, etc.
A properly designed conveyance system maximizes hydraulic efficiency by using the proper material, slope, and size.
Constructed conveyance systems should emulate natural, pre -developed conditions to the maximum extent practical. Field -
verified defined natural drainage ways must be preserved and protecte filling them in and building on top of them is not
an acceptable practice.
Inflow and discharge from the system shall occur at the natural drainage points in the same manner as the pre -developed
condition.
8.2 APPLICABILITY 204� IZ41Y7
All projects shall comply with this Basic Requir ment Conveyance Natural and Constructed regardless of whether the
project meets the regulatory threshold.
8.3 NATURAL AND CONSTRUCTED CHANNELS
8.3.1 CHANNEL ANALYSIS
A channel analysis shall be performed for all constructed channels proposed for a project and for all field -verified existing
natural drainage ways/channels present on -site (refer to Section 8.3.4 for details). The following requirements apply to
the Drainage Report and the road and drainage plans, when applicable:
• Complete channel calculations shall be provided, indicating the design peak flow rates and assumptions, such as
channel shape, slope and Manning's coefficient (see Table 5-4);
• Calculations, including the velocity, capacity, and Froude number shall be provided for each distinct channel
segment whenever the geometry of the channel changes (i.e. if the slope, shape or roughness changes significantly);
• The centerline and direction of flow for all constructed drainage ditches or natural channels within the project
limits are to be clearly shown on the construction plans and basin map. For all proposed channels, stationing
information shall be provided at all angle points;
• Calculations shall support the riprap area, thickness, riprap size and gradation, and filter blanket reinforcement for
all channel protection, which shall be provided when permissible velocities are exceeded (see Table 8-1). This
information shall be included in the plans;
107
Table 8-1
Permissible Velocities for Channels with Erodable Linings,
Based on Uniform Flow in Continuously Wet, Aged, Channels
Soil Type Of Lining
(Earth; No Vegetation)
Maximum Permissible
Velocities (feet/second)
Clear
Water
Fine sand (non -colloidal)
1.5
Sandy loam (non -colloidal)
1.7
Silt loam (non -colloidal)
2.0
Ordinary firm loam
2.5
Volcanic ash
2.5
Fine gravel
2.5
Stiff clay (very colloidal)
3.7
Graded, loam to cobbles (non -colloidal)
3.7
Graded, silt to cobbles (colloidal)
4.0
Alluvial silts (non -colloidal)
2.0
Alluvial silts (colloidal)
3.7
Coarse gravel (non -colloidal)
4.0
Cobbles
5.0
Shales and hard pans
6.0
Source: Special Committee on Irrigation esearch, American Society of Civil Engineers, 1926.
The Froude number shall be checked near the beginning and near the end of a channel that has significant grade
changes to determine if a hydraulic jump occurs (as indicated by the Froude number changing from <1 to >1, or
vice versa). Since it is difficult to correlate the location of a hydraulic jump to the actual location in the field, the
engineer shall propose evenly spaced riprap berms, check dams, or other protective measures to ensure that the
jump does not erode the conveyance facility;
When geosynthetics are used for channel protection, the plans shall clearly specify fabric type, placement, and
anchoring requirements. Installation shall be per the manufacturer's recommendation; and,
Plans for grass -lined channels shall specify seed mixture and irrigation requirements, as applicable.
8.3.2 MINIMUM REQUIREMENTS
Slope
Minimum grades for constructed channels shall be as follows:
• 1.0% for asphalt concrete; and,
• 0.5% for cement concrete, graded earth, or close -cropped grass.
Side Slopes
• Ditch cross -sections shall be trapezoidal; and,
• The side slope of roadside ditches shall be a minimum of 4:1.
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Location
Constructed channels shall not be placed within or between residential lots. Ditches, swales, and channels shall be
located within a drainage parcel. Ditches, swales, or channels may be allowed to traverse through lots in large -lot
subdivisions (lots of 1 acre or more) and consideration may be given to placement within an easement versus a parcel
The City Engineer will review these proposals on a case by -case basis.
Depth
The minimum depth of open channels shall be 1.3 times the flow depth or 1 foot; whichever is greater.
Velocity
Table 8-1 lists the maximum permissible mean channel velocities for various types of soil and ground cover. If mean
channel velocities exceed these values, channel protection is required (refer to Section 8.3.3). In addition, the following
criteria shall apply:
• Where only sparse vegetative cover can be established or maintained, velocities should not exceed 3 feet/second;
• Where the vegetation is established by seeding, velocities in the range of 3 to 4 feet/second are permitted;
• Where dense sod can be developed quickly or where the normal flow in the channel can be diverted until a
vegetative cover is established, velocities of 4 to 5 feet/second are permitted; and,
• On well established sod of good quality, velocities in the range of 5 to 6 feet/second are permitted.
8.3.3 CHANNEL DESIGN
Channel Capacity
Open channels shall be sized using the following variation of Manning'sformula.
Equation 8-1: Q=VA=1.486AR23S"-
n
Where: Q = rate of flow (cfs);
V = mean velocity in channel (feet/second);
A = cross -sectional area of flow in the channel (square feet);
R = hydraulic radius (feet); where R = A/P, and
P = wetted perimeter (feet)
S = channel slope (feet/foot); and,
n = Manning's roughness coefficient (Table 5-4).
Note: Manning's equation will give a reliable estimate of velocity only if the discharge, channel cross-section,
roughness, and slope are constant over a sufficient distance to establish uniform flow conditions. Uniform flow
conditions seldom, if ever, occur in nature because channel sections change from point to point. For practical
purposes, however, Manning's equation can be applied to most open channel flow problems by making conservative
assumptions.
Energy Dissipation Design
An energy dissipater is useful in reducing excess velocity, as a means of preventing erosion below an outfall or spillway.
Common types of energy dissipaters for small hydraulic works are: hydraulic jumps, stilling wells, riprap outfall pads, and
gabion weirs.
Channel Protection
Channel velocities shall be analyzed at the following locations, and if they are found to be erosive, channel protection shall
be provided:
• At the top of a watershed, at the point where the stormwater runoff becomes concentrated into a natural or
constructed channel;
• At all changes in channel configuration (grade, side slopes, depth, shape, etc.), if an erosive velocity is determined
at a change in channel configuration, the velocity shall be evaluated up the channel until the point at which the
velocity is determined not to be erosive; and,
• At periodic locations along the entire channelized route.
109
A material shall be selected that has revetment and armoring capabilities, and the channel shall be analyzed using the
Manning's "n" value for that material to determine if the material will reduce the velocity in the channel. In some
cases, vegetative cover (natural grasses, etc.) may provide excellent protection without changing the flow characteristics
and should be evaluated. If the calculations reveal that common materials such as riprap are not adequate, stronger
protection such as gabions and/or stilling pools may be necessary.
Riprap Protection at Outlets
If the velocity at a channel or culvert outlet exceeds the maximum permissible velocity for the soil or channel lining,
channel protection is required. The protection usually consists of a reach between the outlet and the stable downstream
channel lined with an erosion -resistant material such as riprap.
The ability of riprap revetment to resist erosion is related to the size, shape, and weight of the stones. Riprap-lined
channels are required to have filter fabric under the riprap. Riprap material shall be blocky in shape rather than elongated.
The riprap stone shall have sharp, angular, clean edges. Riprap stone shall be reasonably well -graded and a minimum size
of 6 inches.
Apron Dimensions: The length of an apron (La) is determined using the following empirical relationships that were
developed for the U.S. Environmental Protection Agency (ASCE, 1992):
Equation 8-2: La = 1.8 + (7 Do) for TW < Do/2
DO 3/2
Or
Equation 8-3: La = 3� + (7 Do) fo W > Do/2
DO 3/2
Where: Do = maximum inside tc e dth (feet);
Q = pipe discharge (cfs); and,
T W — tai ater de th (feet).
When there is no well-defined channel downstr of e apron, the width, W, of the apron outlet as shown in Figure 8-1,
shall be calculated using Equation 8-4 or 8-5:
a
w
Figure 8-1— Riprap Revetment at Outfall Schematic
Plan View
110
Equation 8-4: W = 3Do + (0.4 La) for TW > Do/2
Or
Equation 8-5: W = 3Do + La for TW < Do/2
When there is a well-defined channel downstream of the apron, the bottom width of the apron should be at least equal to
the bottom width of the channel and the lining should extend at least 1 foot above the tailwater elevation. The width of the
apron at a culvert outlet should be at least 3 times the culvert width.
Apron Materials: The median stone diameter, D50 is determined from the following equation:
Equation 8-6: D 50 = 0.02 Q4/1
Do (TW)
Where: D50 = the diameter of rock, for which 50% of the particles are finer.
The riprap should be reasonably well graded, within the following gradation parameters:
1.25 < D � < 1.50 and D15 = 0.5 and D m = 0.25
D50 D50 D50
Where: Dmax = the maximum partACe size;
Dram = the minimum particle size; and,
D15 = the diameter of rock, for which 15% of the particles are finer.
Minimum Thickness: The minimum thickness of the riprap ayer shall be 12 inches, Dmax or 1.5*D50, whichever is greater.
qV
Filter Blanket: A filter fabric blanket shall be placed under the riprap.
8.3.4 PRESERVATION OF NATURAL DRAINAGE WAYS (NDW)
New development shall be designed to protect existing natural drainage features that convey or store water or allow it to
infiltrate into the ground in its natural location. Preserving the NDW will help ensure that stormwater runoff can continue to
be conveyed and disposed of at its natural location. Preservation will also increase the ability to use the predominant systems
in conjunction with regional stormwater facilities.
Projects located within the City of Kalispell shall refer to the City of Kalispell's 2008 Storm Water Facility Plan
Update for specific details with regards to the location of NDW.
Definitions
The drainage ways that need to be preserved have been mapped and defined in the City of Kalispell's 2008 Storm Water
Facility Plan Update. Each natural drainage way shall be designed to pass the 100 year 24 hour storm event as described in
the Plan Update. Because every site is unique, the City Engineer shall make interpretations, as necessary, based on site
visits and technical information as to the exact location on aproject site. The City Engineer may also require the project
owner to provide engineering information to assist in this determination.
The maps denoting these drainage ways are not definitive; a computer program was used to identify the drainage ways.
The maps are only one tool that may be used to identify existing natural drainage ways; field verification will typically be
required to fully identify the existence of a drainage way and its significance with regard to a natural conveyance
system.
All projects shall be reviewed for the presence of natural drainage ways mapped in the 2008 Stormwater Facility
Plan, and a determination will be made as to their significance with regard to preservation of natural conveyance and potential
use as part of a regional system.
111
Protection
• No cuts or fills shall be allowed in predominant natural drainage ways except for perpendicular driveway or road
crossings with engineering plans showing appropriately sized culverts or bridges. Natural drainage ways shall be
preserved for stormwater conveyance in their existing location and state, and shall also be considered for use as
regional facilities;
• Less prominent drainage ways in a non-residential development and in a residential development containing lots 1
acre or smaller may be realigned within the development provided that the drainage way will enter and exit the
site at the pre -developed location and that discharge will occur in the same manner as prior to development;
• Realignment of a less prominent drainage way shall be defined as still following the "basic" flow path of the
original drainage way. An acceptable example would be if the drainage way is proposed to be realigned such that
it will follow a new road within the proposed development, and will be left in its existing state or utilized as part of
the project's on -site stormwater system.
• Stormwater leaving the site in the same manner shall be defined as replicating the way the stormwater left the site
in its existing condition. If the drainage way is preserved in its existing location and is left undisturbed, this goal
should be met;
• If the City Engineer accepts the proposal to allow a less predominant drainage way to be routed through the site
via a pipe or approved drainage material, the following additional criteria shall be met:
o Where the less prominent drainage way enters the site, the design shall ensure that the entire drainage
way is "captured" as it enters the site; i.e. the surrounding property shall not be regraded to "neck -down"
the drainage way so that it fits into a drainage easement or tract or structure intended to capture and reroute
the off -site stormwater runoff,
o Where the less prominent drainage way exits the site, the design shall ensure that the stormwater
leaves the pipe, pond or structure a significanKmay
ce from the edge of the adjacent property so
that by the time the stormwater reaches the prondary, its dispersal shall mimic that of the
pre -developed condition; and,
o Since some of the less prominent drainag ays o be useful for managing regional
stormwater, if identified as a significant drainage way (i.e. necessary conveyance for flood
control, or being considered as a confection to a planned regional facility or conveyance route),
then the drainage way may be subject to the same limitations and criteria as a predominant drainage
way.
• The size of the tract or easement containing the draurayge way shall be determined based on an analysis of the
existing and proposed stormwater flows directed to these drainage systems and any access and maintenance
requirements found in this manual; and,
• All new development containing lots that 1 acre or smaller shall be required to set aside the drainage way as
open space in a separate parcel. For new development containing lots that are greater than 1 acre, the drainage way
may be set aside in either a parcel or an easement.
8.4 CULVERTS
A culvert is a short pipe used to convey flow under a roadway or embankment. Culverts are used to pass peak flow from
defined drainage ways identified on contour maps. A culvert shall convey flow without causing damaging backwater flow
constriction, or excessive outlet velocities. Factors to be taken into consideration in culvert design include design flows, the
culvert's hydraulic performance, the economy of alternative pipe materials and sizes, horizontal and vertical alignment, and
environmental concerns.
8.4.1 CULVERT ANALYSIS
When applicable, the following items shall be included in the Drainage Report and on road and drainage plans:
• Complete culvert calculations that state the design peak flow rates, velocities at the inlet and outlet, flow
control type, and design information for the culvert such as size, slope, length, material type, and Manning's
coefficient (refer to Table 8-2);
• Headwater depths and water surface elevations for the design flow rate;
• Roadway cross-section and roadway profile;
• Location information for each of the culvert inverts and invert elevations;
• Type of end treatment (wingwall, flared end sections, etc); and,
• Wall thickness.
112
8.4.2 MINIMUM REQUIREMENTS FOR CULVERTS
Peak Flow Rate
• Culverts shall be sized to handle the design peak flow rates calculated using the methods described in Section 5
and the design criteria specified in Section 2;
• To avoid saturation of the road base, culverts shall be designed such that the water surface elevation for the
design storm event does not exceed the elevation of the base course of the roadway; and,
• Culverts shall be designed to convey the 100-year peak storm event without damage.
Table 8-2
Manning's Roughness Coefficient (n)
For Culverts
Material Type
n
Reinforced concrete pipe (RCP)
0.013
Ductile iron
0.012-.015
HDPE
0.013
CMP
0.024
HDPE = high -density polyethylene; CMP = corrugate etal pipe. Manning's
Coefficient (n) can also be based on manufactures s cations.
Allowable Headwater Elevation
• Headwater is the depth of water at the culvert entrance a a given design flow. Headwater depth is measured
from the invert of the culvert to the water surface; and, -
• Culverts shall be designed to carry the design runoff wi a headwater depth less than 2 times the culvert
diameter for culverts 18 inches or less in diameter, and less than 1.5 times the culvert diameter for culverts
more than 18 inches in diameter. A'�
Velocity and Slope
To avoid silting, the minimum velocity of flow thro gh culverts shall be 2.5 feet/second and the minimum slope shall be
0.5%.
Diameter
Table 8-3 lists required minimum culvert diameters.
Table 8-3
Minimum Culvert Sizes
Culvert Location
Minimum Size (inches)
Under public roads
12
Under private roads
12
Under driveways/approaches
12
Allowable Pipe Material and Pipe Joints
• Corrugated metal pipe:
o Joints shall be rubber gasketed and securely banded.
• Ductile iron;
o Joints shall be flanged, bell and spigot, or restrained mechanical joints;
113
Reinforced concrete:
o Joints shall be rubber gasketed;
High -density polyethylene (HDPE):
o Joints shall be joined by split corrugated coupling, with gaskets; and,
o Pipes and fittings shall be manufacture for high density polyethylene resin which shall meet or
exceed the requirements of Type 111, category 3, 4, 5, grade P23, P33 or P34, Class C per ASTM
D1248. In addition the pipe shall comply with all material and stiffness requirements of
AASHTO M294.
Pipe Anchoring
For grades greater than or equal to 20%, anchors are required unless calculations or the manufacturer's
recommendations show that they are not necessary.
Placement/Alignment
Generally, culverts shall be placed on the same alignment and grade as the drainage way. Design shall consider changes of
conditions over time and use design measures such as:
• Cambering or crowning under high tapered fill zones;
• Raising intakes slightly above the flow line to allow for sedimentation;
• Using cantilevered outfalls away from road banks to allow for toe erosion; and,
• Using drop inlets or manholes to reduce exit velocities on steep terrain.
Angle Points
The slope of a culvert shall remain constant throughout the entire lengthke
culvert. However, in situations where existing
roadways are to be widened, it may be necessary to extend an existin t a different slope; the location where the slope
changes is referred to as the angle point. The change in slope tends rocation in the culvert that catches debris and
sediment If an extension of a culvert is to be placed at a differe a existing culvert, a manhole shall be provided
at the angle point to facilitate culvert maintenance.
Outfalls
Outfalls shall conform to the requirements of all federal, state, and local regulations. Erosion control shall be provided at the
culvert outfall. Refer to Section 8.3.3 for additional information regarding outfall protection.
Structural Design
For culverts under roadways, the amount of cover r the culvert is defined as the distance from the top of the pipe to the
bottom of the pavement. It does not include asphalt or concrete paving above the base. The minimum amount of cover is 2 feet
for culverts. All pipe designs shall meet AASHTO HS-20 loading criteria.
Also, extreme fill heights (20 feet or greater) may cause structural damage to pipes and will require a special design or
adherence to the manufacturer's recommendations. Refer to manufacturers requirements for the maximum cover for
different pipe materials and sizes.
End Treatments
Culverts greater than 18 inches in diameter shall have end treatments. The type of end treatment used on a culvert depends on
many interrelated and often conflicting considerations:
• Projecting Ends is a treatment in which the culvert is simply allowed to protrude out of the embankment. This is
the simplest and most economical. There are several disadvantages such as susceptibility to flotation and erosion,
safety when projecting into a roadway clear zone (an area beyond the traveled roadway provided for recovery of errant
vehicles), and aesthetic concerns;
• Beveled End Sections consist of cutting the end of the culvert at an angle to match the embankment slope
surrounding the culvert Beveled ends should be considered for culverts 6 feet in diameter or less. Structural
problems may be encountered for larger culverts not reinforced with a headwall or slope collar;
• Flared End Sections are manufactured culvert ends that provide a simple transition from culvert to a
drainage way. Flared end sections are typically only used on circular pipe or pipe arches. This end treatment
is typically the most feasible option in pipes up to 48 inches in diameter. Safety concerns generally prohibit their
use in the clear zone for all but the smallest diameters;
• Headwalls are concrete frames poured around a beveled or projecting culvert. They provide structural support and
eliminate the tendency for buoyancy. They are considered feasible for metal culverts that range from 6 to 10 feet in
114
diameter. For larger diameters, a slope collar is recommended. A slope collar is a reinforced concrete ring that
surrounds the exposed culvert end; or,
• Wincwalls and Aprons are intended for use on reinforced concrete box culverts. Their purpose is to retain and protect
the embankment, and provide a smooth transition between the culvert and the channel.
8.4.3 CULVERT DESIGN
Culvert analysis is typically performed using commercially available computer software. If hand calculations are
proposed, example calculations can be found in technical publications and open channel hydraulics manuals.
8.5 STORM DRAIN SYSTEMS
A storm drain system is a network of pipes that convey surface drainage from catch basins or other surface inlets,
through manholes, to an outfall.
The design of storm drain systems shall take into consideration runoff rates, pipe flow capacity, hydraulic grade line, soil
characteristics, pipe strength, potential construction problems, and potential impacts on down -gradient properties.
8.5.1 PIPE ANALYSIS
The following items shall be included in the Drainage Report, or on road and drainage plans:
• A basin map showing on -site and off -site basins contributing nmoffto each inlet, which includes a plan view
of the location of the conveyance system;
• Complete pipe calculations that state the design peak flow rate d design information for each pipe run, such
as size, slope, length, material type, and Manning's coeffi ' (see Table 8-4);
• Velocities at design flow for each pipe run;
• The hydraulic grade line at each inlet, angle point, o et; d,
• The minimum depth from finish grade to pipe in rt an e minimum pipe slope necessary to satisfy the
freeboard and self-cleaning velocity requirement b provided.
able 8-4
Manning's oughness Coefficient (n)
N For Closed Systems
Material Type
n
Reinforced concrete pipe (RCP)
0.013
Ductile iron
0.012-.015
HDPE
0.013
PVC (only allowed in closed system)
0.012
HDPE = high -density polyethylene; PVC= Polyvinyl chloride,
Manning's Coefficient (n) can also be based on manufactures specifications.
Allowable Pipe Material and Pipe Joints
• Corrugated metal pipe:
o Joints shall be rubber gasketed and securely banded.
• Ductile iron;
o Joints shall be flanged, bell and spigot, or restrained mechanical joints;
• Reinforced concrete:
o Joints shall be rubber gasketed;
• PVC Pipe
o Pipe shall be install following procedures outlined in ASTM D2321;
o Joints shall conform to ASTM D3212, and gasket shall conform to ASTM F477;
o Pipe must be SDR 35 or thicker and meet the requirements of ASTM D3034;
• High -density polyethylene (HDPE):
115
o Joints shall be joined by split corrugated coupling, with gaskets;
o Pipes and fittings shall be manufacture for high density polyethylene resin which shall meet or
exceed the requirements of Type I11, category 3, 4, 5, grade P23, P33 or P34, Class C per ASTM
D1248 or ASTM D3350 minimum cell classification 324420C. In addition the pipe shall comply
with all material and stiffness requirements of AASHTO M294-Type S, M 252 M-96-Type S,
MP7-01, F 667-97, and F 405-97.
o ADS N-12 smooth interior pipe and Contech A-2000 PVC Drainage pipe, which meets all
required specification can be used or an approved equal.
8.5.2 MINIMUM REQUIREMENTS
Peak Flow Rate
Closed pipe systems shall be sized to handle the design peak flow rates. These peak rates can be calculated using the
methods described in Section 5 and the design criteria specified in Section 2.
Hydraulic Grade Line
The hydraulic grade line (HGL) represents the free water surface elevation of the flow traveling through a storm drain
system. Pipes in closed systems will be sized by calculating the HGL in each catch basin or manhole. A minimum of 0.5
feet of freeboard shall be provided between the HGL in a catch basin or manhole and the top of grate or cover.
Pipe Velocities and Slope
The pipe systems shall be designed to have a self-cleaning velocity of 2.5 feet/second or greater calculated under full
flow conditions even if the pipe is only flowing partially full during the design storm.
Pipe velocities should not be excessively high since high flow velocities (approaching and above 10 feet/second) cause
abrasion of the pipes. When the design velocities are 10 feet/second or gr er, manufacturer's recommendations
demonstrating that the pipe material can sustain the proposed velocities s 1 be provided.
When the grade of a storm pipe is greater than or equal to 20%, pipe anchors are required at the joints, at a minimum,
unless calculations and manufacturer's recommendations demonstrate that pipe anchors are not needed. Pipe
anchor locations are to be defined on the plans, and a pipe anchor detail shall be referenced or provided.
Pipe Diameter and Length
The minimum pipe diameter shall be 12 inches, d e maximum length of pipe between junctions shall be no greater than
300 feet. No pipe segment shall have a diameter s ler than the upstream segments.
Placement and Alignment
No storm drain pipe in a drainage easement shall have its centerline closer than 5 feet to a private rear or side property
line. A storm drain located under a road shall be placed in accordance with the City Engineer's requirements or standard
plans. A storm drain system located in the road shall not be placed vertically under the curb and gutter.
If it is anticipated that a storm drain system may be expanded in the future, provisions for the expansion shall be
incorporated into the current design.
OuyWls
Pipe outfalls shall be placed on the same alignment and grade as the drainage way. Outfalls shall conform to the
requirements of all federal, state, and local regulations. Erosion control is required at the storm system outfalls. Refer to
Section 8.3.3 for additional information regarding outfall protection.
Structural Design
The amount of cover over the pipe is defined as the distance from the top of the pipe to the bottom of the pavement. It does
not include asphalt or concrete paving above the base. The minimum amount of cover is 2 feet for culverts. All pipe designs
shall meet AASHTO HS-20 loading criteria.
Inverts at Junctions
Whenever two pipes of the same size meet at a junction, the downstream pipe shall be placed with its invert 0.1 feet below
the upstream pipe invert. When two different sizes of pipes are joined, pipe crowns shall be placed at the same
elevation. The exception to this rule is at drop manholes. Exceptions may be allowed by the City Engineer when
topographic conditions will significantly impact the depth of the disposal location.
Combined Systems
Combined sanitary and stormwater sewer systems are prohibited.
8.5.3 PIPE DESIGN
To analyze the conveyance capacity of a closed pipe system, the following general steps may be followed when steady
flow conditions exist, or conditions can be accurately approximated assuming steady flow conditions:
1. Estimate the size of the pipes assuming a uniform flow condition, using Equation 8-1. Refer to Table
for Manning's coefficient values;
2. For the pipe sizes chosen, determine uniform and critical flow depth;
3. Determine if upstream (accelerated) flow conditions or downstream (retarded) flow conditions exist.
Subcritical flow occurs when downstream conditions control, supercritical flow occurs when
upstream conditions control. Determine what flow regime will occur by comparing uniform flow
depth, critical flow depth, and initial flow depth. Identify hydraulic jump locations, and where any
other discontinuity of flow depth will occur; and,
4. Conduct a more detailed analysis by computing the hydraulic grade line. The direct step method or
standard step method is often used to calculate the hydraulic grade line. For supercritical flow, begin
at the upstream end and compute flow sections in consecutive order heading downstream. For sub -
critical flow, begin at the downstream end and co to flow sections in consecutive order heading
upstream.
The analysis of closed pipe systems is typically done using co ercially available computer software packages. If hand
calculations are proposed, example calculations can be found in technical publications on open channel hydraulics, such as:
"Handbook of Hydraulics", by Brater and King; and "Open -Channel Hydraulics" by French.
8.6 GUTTERS ACLowy
A gutter is a section of pavement adjacent to a roadway that conveys water during a storm runoff event. Gutter flow
calculations are necessary to establish the spread of water onto the shoulder, parking lane, or travel lane. Roadways shall
have an adequate non -flooded width to allow for the passing of vehicular traffic during the design storm events and shall
not over top the curb onto the boulevard or sidewalk. The non -flooded width (L) is shown in Figure 8-2 and the minimum
non -flooded widths for various road classifications are outlined in Table 8-5.
L
GUTTER FLOW CURB
- r
SIDEWALK
Figure 8-2 — Non -Flooded Road Width (L)
117
Table 8-5
Non -Flooded Road Width Requirements
Road Classification
Non -Flooded Width (L)
Private Road
12 feet
Local Street
12 feet
Collector Street, 2 Lane
16 feet
Arterials
Per City Engineer
Other road types
Per City Engineer
The non -flooded width shall be evaluated at low points and at proposed inlet locations. The non -flooded width shall also
be evaluated at intersections. Bypass flow shall be limited to 0.1 cfs at intersections and at the project boundary.
Non -flooded width and flow depth at the curb are often used as criteria for spacing pavement drainage inlets (curb or
grate inlets). Drainage inlets shall be spaced so that the non -flooded width requirements are met and stormwater does not
flow over the back of the curb. Spacing shall not exceed 400 feet regardless of flooded width and flow depth compliance.
Generally, inlets shall be placed in the uphill side of the curb return. Additionally, the first inlet shall not be located more
600 feet from the point where the gutter flow path originates.
Gutters shall have a minimum longitudinal slope of 0.5%.
8.6.1 GUTTER ANALYSIS
The drainage report shall include complete gutter calculations that state the design peak flow rates, design flow depth, road
cross slope, road grade, and non -flooded width.
The equation for calculating gutter flow is a modified rsion of Manning's equation.
Equation 8-7: QN=)6 sX1.67 SL 0.5 T 2.67
n
Where: Q = flow rate (cfs);
n = Manning's coefficient (from Table 8-8);
SL = longitudinal slope of the gutter (feet/foot);
Sx = cross slope (feet/foot); and,
T = spread (feet).
[K®
Table 8-6
Manning's Roughness Coefficients (1)
for Street and Pavement Gutters
Type of Gutter or pavement
n
Concrete gutter, troweled finish
0.012
Asphalt Pavement
Smooth Texture
0.013
Rough Texture
0.016
Concrete pavement
Float finish
0.014
Broom finish
0.016
Source: Federal Highway Administration (FHWA), Hydraulic Engineering
Circular No. 22, Second Edition
8.6.2 GUTTER DESIGN
Uniform Gutter Section
Uniform gutter sections have a cross slope that is equal to the cross slope of the shoulder or travel lane adjacent to the
gutter (see Figure 8-3). The spread (T) in a uniform gutter section e calculated using Equation 8-7 and solving
for T (spread) as follows:
Equation 8-8:
0.375
T = l.b? 0.5
X L
Figure 8-3 — Uniform Gutter Section
119
An example calculation for determining the non -flooded width and the depth of flow for a uniform gutter section is
provided in Appendix 8A.
8.7 DRAINAGE INLETS
Drainage inlets are used to collect runoff and discharge it to a storm drainage system. They are typically located in
gutter sections, paved medians, and roadside and median ditches.
Inlets most commonly used in the City of Kalispell are as follows:
• Grate Inlets consist of an opening in the gutter or ditch covered by a grate. They perform satisfactorily over a wide
range of longitudinal slopes. Grate inlets generally lose capacity as the grade of the road, gutter or ditch increases.
• Curb Inlets (combination inlets) consist of both a curb -opening and a grate inlet. They offer the advantages of both
grate and curb inlets, resulting in a high capacity inlet.
There are many variables involved in designing the number and placement of inlets, and in determining the hydraulic
capacity of an inlet. The hydraulic capacity of a storm drain inlet depends upon its geometry as well as the characteristics
of the gutter flow. Inlet capacity governs both the rate of water removal from the gutter and the amount of water that can
enter the storm drainage system. Inadequate inlet capacity or poor inlet location may cause flooding on the roadway
resulting in a hazard to the traveling public.
8.7.1 MINIMUM REQUIREMENTS
Peak Flow Rate
The capacity of drainage inlets shall be determined using the design peak flow rates. These rates can be calculated using the
methods described in Section 5 and the design storm criteria specified in Section 2. Bypass flow shall be limited to 0.1 cfs at
intersections and at the project boundary.
Structures
• Storm drain manhole ring and cover shall be East Jordan Ir Works Product No. NCR07-1738B, Olympic
Foundry 11-3804, or approved equal. The c shall be marked Storm or Storm Sewer. Open grates shall be used
only in paved area;
• Storm drain inlets shall be as follows:
o Straight (SD-6) and C Gutte (SD-4) Applications ..... East Jordan Iron Works #7222,
Olympic Foundry SM4913, or approved equal; and,
o Drive Over Curb & Gutter (SD-5) Applications..... East Jordan Iron Works #7711, Olympic
Foundry SM44, or approved equal.
• Catch basins shall be used in all public and private roads;
• Catch basins, inlets, and storm manholes shall be placed at all breaks in grade, pipe size change, and horizontal
alignments;
• Catch basins, inlets, and storm manholes shall have a minimum 24" sump below the lowest pipe invert elevation;
• Pipe runs shall not exceed 400 feet for all pipe sizes; and,
• Horizontal and vertical angle points shall not be allowed in a storm system unless a manhole is provided for
cleaning.
Grates
• All grate inlets shall follow requirement set in the City of Kalispell Standards for Construction and Design;
• Grate inlets on grade shall have a minimum spacing of 20 feet to enable the bypass water to reestablish its flow
against the face of curb;
• Drainage inlets shall not be located on the curved portion of a curb return;
• Grates shall be depressed to ensure satisfactory operation; the maximum depression is 1 inch; and,
• Inlets with larger openings may be used for additional capacity but must be approved by the City Engineer.
Curb Inlets
• All curb inlets shall follow requirement set in the City of Kalispell Standards for Design and Construction.
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Concrete Aprons
• Concrete aprons shall be used at the entrance to all open grate manholes, catch basins, and curb inlets. Apron shall
slope toward the grate as shown on the standard details. Refer to the City of Kalispell Standards for Design and
Construction for details.
• A minimum 2-foot apron shall be used with inlets when no curb and gutter is present. Refer to the City of
Kalispell Standards for Design and Construction for details.
Inlet Placement
• Inlets shall be located at intersections to prevent the flow from crossing the intersection.
• Inlets at intersection shall be located so they do not encroach upon the curb return.
• No drainage structure shall be permitted at an ADA ramp.
8.7.2 DRAINAGE INLET DESIGN
Grate Inlets, Continuous Grade
The capacity of an inlet on a continuous grade can be found by determining the portion of the gutter discharge directly
over the width of the inlet. On continuous grades (assuming that the grate has the capacity to intercept the entire flow
rate directed toward it), the amount of stormwater intercepted by a grate is equal to the amount of stormwater runoff
flowing directly over the grate plus the amount that flows in over the side of the grate through the slats/bars. The analysis
shall include a 35% clogging factor. The use of formulas for side flow interception for grate inlets found in SHWA
Hydraulic Engineering Circular No. 22 (HEC-22) will be accepted.
The following procedure is most accurate when velocities are in the range of 3 to 5 feet/second at a 2% or 3% longitudinal
slope. For instances where the velocity is found to exceed 5 feet/second, additional intermediate inlets can be
added, contributing basins redefined, and the associated velocities recalculated. While adding inlets is one solution to
reducing the velocity, more information may be found regarding to affect of 'de flow by consulting the HEC-22 Circular,
Section 4.4 Drainage Inlet Design. Note that commercially avail oftware may be used to determine grate inlet
capacity.
The capacity of a grate inlet on a continuous grad may be calculated using the procedure outlined below. Figure 8-5
identifies key parameters. Example calculations for g to *inlets on a continuous grade for a uniform gutter section are
provided in Appendix 8B.
1. Determine the runoff from the con 'outing b sin at the high point to the first inlet. This is the amount of runoff
that could be intercepted by the first inlet. Depth (d) can not exceed the top of the curb.
i
2. Select an inlet and note the grate width (GW) in the calculations (refer to Table 8- ).
Figure 3-5 —Typical Grate Inlet Cross -Section
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TABLE 8-7
Allowable Width and Perimeter
for Grate Capacity Analysis
Allowable Width
on a Continuous
Structure Type
Grade (feet)
Curb Inlet'
1.41
Roll -Over Grate Inlei
1.43
1 Bases on Olympic Foundry SM49B
2 Based on Olympic foundry SM44
Note: Readers should review the most current versions of the City Standard for Design
and construction for any revisions that may have been made to values provided in this
table.
3. Analyze the most upstream inlet. The width of flow (T) is calculated using the procedure described in Section
8.6.2. Verify that T is within the allowable limit (see Table 8-5, and then determine the amount of flow
intercepted by the grate (basin flow — bypass flow).
The inlet bypass flow on a continuous grade is computed llows:
Equation 8-9
8
B _ (T - W) 3
M
Where: QBp = portion of flow ou e the grate width (cfs);
Q = total flow of gutter approaching the inlet (cfs);
T = spread, calculated from the gutter section upstream of the inlet (feet); and
GW = grate inlet width perpendicular to the direction of flow (feet), see Table 8-9.
5. The velocity shall not exceed 5 feet/second. The velocity of flow directly over the inlet is calculated as follows:
Equation 8-10
— BP
Where: V1 = velocity over the inlet (feet/second);
SX = cross slope (feet/foot); and,
d = depth of flow at the face of the curb (feet),
given by: d = (7)(Sx )
If the non -flooded road width does not meet the minimum criteria, an additional inlet should be placed at
an intermediate location and the procedure repeated.
If the velocity exceeds 5 feet/second then side flow shall be considered using the method outlined in
HEC-22 Circular, Section 4.4 Drainage Inlet Design.
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6. The analysis is then repeated with the next inlet. The bypass flow (QBp) from the previous inlet shall be added to
the flow from the contributing basin to determine the total flow to the inlet at the station being analyzed.
7. The last inlet may require an adjustment of spacing (usually smaller spacing) in order to prevent a bypass flow
to the project boundaries.
Other Drainage Inlets
The design for the drainage inlets other than Grate Inlets, Continuous Grade described above shall be calculated
using the procedure outlined in SHWA Hydraulic Engineering Circular No. 22 (IEC-22). Example calculations can
also be found in the 2008 Spokane Regional Stormwater Manual, Chapter 8.
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APPENDIX 8A - EXAMPLE CALCULATION:
NON -FLOODED WIDTH (UNIFORM GUTTER
SECTION)
GIVEN
A crowned road with a uniform gutter section (as illustrated),
assuming an equal flow rate on each side of the road.
• Flow rate (Q) = 4.2 cfs
• Gutter width (W) = 1.5 feet
• Road/Gutter cross slope (SX) = 0.02feet/foot
• Longitudinal slope (SL) = 0.01 feet/ft
• Manning's friction coefficient, n = 0.016
• Road width (RW) = 30 feet
CALCULATIONS
G`�
I--" T
1. Calculate the spread (T) for half of the roadway using Equation 8-8.
0.375 (4.O.01� )0375
T_ 0. .5.67 0.5 0.5 )1.67 .01 Y.5 =1 feet
2. Calculate the non -flooded width using the following relationship for crowned roadways, and then
verify that the non -flooded width is within the allowable limit (refer to Table 8-5:
Non -flooded width = 2[(1/20W)+W—T)]
2[(1/2)(30) + 1.5—12.4)]
8.2 feet < 12 feet FAIL*
* Table 8-5 indicates that the minimum non -flooded width is 12 feet for roads. Therefore, the design fails to
meet the required non -flooded road width criteria. The design will need to be altered (i.e. try an additional inlet
placed at an intermediate location, contributing basins redefined, new flow rates calculated, and the above
steps repeated).
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APPENDIX 8B - EXAMPLE CALCULATION:
GRATE INLET CAPACITY (UNIFORM GUTTER
SECTION)
WISM21
A crowned private road with a uniform gutter section (as illustrated),
assuming an equal flow rate on each side of the road.
• Flow rate (Q) = 2.5 cfs
• Gutter width (W) = 1.5 ft
• Grate width (GW) =1.67 feet
• Road/Gutter cross slope (S,,) = 0.02 feet/foot
• Longitudinal slope (SL) = 0.03 feet/foot
17
• Manning's friction coefficient, n = 0.016
• Road width (RW) = 30 feet
CALCULATIONS
1. Determine the runoff from the contributing basin at th high point to the fast inlet;
• For this example, the design flow rate (Q) is given as 2.5 cfs
2. Select an inlet and note the grate wid
• For this example, the grate width (GW) is given as 1.67 ft
3. Calculate the spread (r) for half of the roadway using Equation 8-8.
0375 0.375
T—_ Q n _ {2.5X0.016) (0.56 St' Si5) 0.56 (0.02)"(0.03)°5—$•3lfeet
125
4. Calculate the non -flooded width using the following relationship, and then verify that the non -flooded width is
within the allowable limit (refer to Table 8-5):
Non -flooded width = 2[(1/2)(RW)+W—T)]
= 2[(1/2)(30) + 1.5 — 8.31)]
= 16.38 feet > 12 feet OK*
* Table 8-5 indicates that the minimum non -flooded width is 12 feet for private roads. Therefore, design has met
the required non -flooded road width criteria.
5. Calculate the inlet bypass flow using Equation 8-9:
• With 35% clogging factor, grate width (GW) = 1.67(1 - 0.35) = 1.09'
[(T) — 3 = . 8. 1-1.09 3=1.7.cfs
T 8.1
Therefore the capacity of the inlet = 2.5 —1.7 .78 cfs
6. Verify that the velocity does not exceed 5 feet/second. Th e oci ow directly over the inlet is calculated using
Equation 8-10 (where d = T Sx):
— �� .5 —1.72
VI= — 2�— 4.61f /s < feet/second OK*
(GFF)[d-0.5( )(S ] 1.04(8.3i)(0.02)-0.5(1.09X.o�,}I-
12
* *Refer to Section 8.7.2 for guidance when the velocity exceeds 5 feet/second.
7. The analysis is then repeated with the next inlet. The bypass flow (QBp) from the previous inlet shall be added
to the flow from the contributing basin to determine the total flow (Q) to the inlet at the station being analyzed.
126
SECTION 9 - EROSION AND SEDIMENT
CONTROL DESIGN
9.1 INTRODUCTION
Stormwater Management is increasingly important for the purpose of maintaining clean water and preserving waterbodies
such as streams, rivers, and lakes. The City of Kalispell's Stormwater Management Ordinance 1600 went into effect May 2,
2007, as mandated under the Federal Clean Water Act (CWA) and the Montana Pollution Discharge Elimination (MPDES)
regulation. These regulations are designed to improve water quality in waterbodies by reducing the amount of pollutants
that stormwater collects and carries into storm conveyance systems.
This section lists the steps for developing a construction site Stormwater Management Plan (also known as an Erosion and
Sediment Control Plan (ESC). Controlling erosion and preventing sediment and other pollutants from leaving the
project site during construction can be achieved by implementing the best management practices (BMPs) identified in this
section. The ESC plan shall outline specific construction BMPs for a project site to avoid adverse stormwater impacts from
construction activities on water resources, roads, drainage facilities, surrounding properties and other improvements.
Potential impacts due to erosion and sedimentation include:
• Sediment accumulation in culverts, storm drains and open channels, resulting in decreased capacities and the
potential for increased flooding and increased maintenance f quency;
• Sedimentation of storage ponds and swales, resulting in decre infiltrative and storage capacity, and the potential
for increased flooding and failure;
• Destruction of vegetation, topsoil and seeds, mak' r stab shment of vegetation difficult;
• Increased turbidity, reducing water quality in w er bo ; and,
• Air pollution due to fugitive dust.
Implementation of an effective construction site stormwater man gement plan may help to reduce these potential
impacts as well as other unforeseen environmentaPimpacts and associated costs.
9.2 APPLICABILITY
A City Stormwater Management Plan for construe sites is required for land -disturbing activities which include, but are
not limited to, excavation, planting, tilling, and grading, which disturbs the natural or improved vegetative ground cover so
as to expose soil to the erosive forces of rain, stormwater runoff or wind. All installations and maintenance of franchise
utilities such as telephone, gas, electric, etc., shall be considered land disturbing activities.
The following land -disturbing activities require a City Stormwater Management Permit:
• Any activity where the total volume of material disturbed, stored, disposed of or used as fill exceeds five (5)
cubic yards; or,
• Any activity where the area disturbed exceeds one thousand (1000) square feet provided it does not obstruct a
watercourse, and is not located in a floodplain.
The Stormwater Management Plan shall adhere to Ordinance 1600 and be submitted prior to any land -disturbing
activity. The following is a summarization of the standards set in Ordinance 1600.
9.3 EROSION AND SEDIMENT CONTROL (ESC) PLAN
A professional with a good working knowledge of hydrology and ESC practices, must prepare the ESC plan. A copy of
the ESC plan must be located on the construction site or within reasonable access to the site. As site construction progresses,
the ESC plan may require modification to reflect changes in site conditions.
The ESC plan must accompany the road and drainage plans, grading plan, or permit request and should be integrated into
the grading plan whenever possible. It must contain sufficient information to demonstrate to the City Engineer that potential
127
problems associated with erosion, sediment, and pollution have been adequately addressed for the proposed project.
The drawings and notes should be clear and concise and describe when and where each BMP is to be implemented.
9.3.2 MINIMUM REQUIREMENTS FOR ESC PLANS
At a minimum, all ESC plans must be legible, reproducible and on good quality, and must contain the following
information:
• Description of project, list of the locations of any existing water bodies and/or stormwater systems;
• Summary description of ESC BMPS utilized; and,
• Construction Sequence.
9.3.3 BEST MANAGEMENT PRACTICES FOR ESC PLANS
BMPS must be used to comply with the requirements of this section. It is not the intent of this section to limit
innovative or creative efforts to effectively control erosion and sedimentation. Experimental ESC management
practices to improve erosion control technology and meet the purpose and intent of this section are encouraged as a
means of solving erosion and sedimentation problems. It is important to note that not only do new facilities and
off -site properties need to be protected from erosion and sedimentation, but existing facilities on -site or downstream also
need to be evaluated and protected if there is potential for damage due to lack of erosion control.
As the season and subsequent site conditions dictate, alterations to existing ESC BMPS may be warranted or additional
ESC measures may be required. Note that items below are considered suggested general erosion and sedimentation
control notes and guidelines. The notes can be used on the ESC plan, when applicable to a given project site.
BMPS referenced in this section are from the Montana Departure Transportation Erosion and Sediment Control
Best Management Practices Manual (MDT ESC Manual). Detailed examples and descriptions of these BMPS are
included in MDT ESC Manual. At a minimum, the following items shalf be addressed in the ESC plan:
1. Construction Sequence
• Install temporary ESC BMPS; constructing sediment trapping BMPS as one of the first steps prior to grading;
• Clear, grub and rough grade for roads, teWorary access points and utility locations;
• Stabilize roadway approaches and temporary access points with the appropriate construction entry BMP;
• Temporarily stabilize, through re -vegetation or other appropriate BMPS, lots or groups of lots in situations where
substantial cut or fill slopes are a result of the site grading;
• Construct roads, buildings, permanent stormwater facilities (i.e. inlets, ponds, UIC facilities, etc.);
• Protect all permanent stormwater facilities utilizing the appropriate BMPS;
• Install permanent ESC controls, when applicable; and,
• Remove temporary ESC controls when:
o Permanent ESC controls, when applicable, have been completely installed;
o All land -disturbing activities that have the potential to cause erosion or sedimentation problems have
ceased; and,
o Vegetation had been established in the areas noted as requiring vegetation on the accepted ESC
plan on file with the City Engineer.
2. Clearing Limits
• Distinctly mark all clearing limits, both on the plans and in the field— taking precaution to visibly mark separately
any flood plain areas, and trees that are to be preserved —prior to beginning any land -disturbing activities,
including clearing and grubbing; and,
• If clearing and grubbing has occurred, there is a window of 14 days in which construction activity must begin,
otherwise the cleared area must be stabilized.
Suggested BMPS:
• Preserving Natural Vegetation
• Flood Plain Delineation
• Buffer Zones
• High Visibility Plastic or Metal Fence
• Stake and Wire Fence
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3. Construction Access Route
• Limit access for construction vehicles to one route whenever possible;
• Stabilize the construction access routes to minimize the tracking of sediment onto roadways;
• Install temporary vehicle tracking approach at site entrance locations;
• Inspect all roadways, at the end of each day, adjacent to the construction access route. If it is evident that sediment has
been tracked offsite and/or beyond the roadway approach, removal and cleaning is required;
• If sediment removal is necessary prior to street washing, it shall be removed by shoveling or sweeping and
transported to a controlled sediment disposal area;
• If street washing is required to clean sediment tracked offsite, once sediment has been removed, street wash
wastewater shall be controlled by pumping back on -site or otherwise prevented from discharging into systems
tributary to waters of the state; and,
• Locate wheel washes or tire baths, if applicable to ESC plan, on site. Dispose of wastewater into a separate
temporary on -site treatment facility in a location other than where a permanent stormwater facility is
proposed.
Suggested BMPs:
• Stabilized Construction Entrance/Exit
• Stabilized Construction Roadways
• Entrance/Outlet Tire Wash
• Rumble Strip/Cattle Guard
• Construction Road/Parking Area Stabilization
4. Install Sediment Controls
• Retain the duff layer, native topsoil, and natural v et tion i undisturbed state to the maximum extent
practical;
• Pass stormwater runoff from disturbed areas through se ent pond prior to leaving a construction site or
discharging to an infiltration facility;
• Keep sediment on the project site, to the maximum extent practical, in order to protect adjacent properties, water
bodies, and roadways;
• Stabilize earthen structures such as d dikes, and diversions with either quarry spalls, seed or mulch, or a
combination thereof,
• Locate sediment facilities such that they wl not interfere with natural drainage channels or streams; and,
• Inspect sediment control BMPs bi-weekly at a minimum, daily during a storm event, and after any discharge from
the site (stormwater or non-stormwater). The inspection frequency may be reduced to once a month if the site is
stabilized and inactive.
Suggested BMPs:
• Check Dams
• Street Sweeping and Vacuuming
• Silt Fence
• Vegetated Strip
• Straw Wattles (fiber rolls)
• Sediment Trap
• Desilting Basin
5. Soil Stabilization
• Select appropriate BMPs to protect the soil from the erosive forces of raindrop impact flowing water and wind, taking
into account the expected construction season, site conditions and estimated duration of use;
• Control fugitive dust from construction activity in accordance with state and local air quality Ordinances;
• Stabilize exposed unworked soils (including stockpiles), whether at final grade or not, within 14 days;
• Soils must be stabilized and seeded by October 15 of every year; and,
• Stabilization practices include, but are not limited to, temporary and permanent seeding, sodding, mulching,
plastic covering, erosion control fabric and mats, soil application of polyacrylamide (PAM) and the early application
of gravel base on areas to be paved, and dust control.
129
Suggested BMPs:
• Scheduling
• Preservation of Existing Vegetation
• Temporary Seeding
• Erosion Seeding
• Mulching (straw, wood)
• Geotextiles, Plastic Covers, and Erosion Control Nets/Blankets/Mats
• Sodding
• Topsoiling
• Polyacrylamide (PAM) for Soil Erosion Protection
• Surface Roughening
• Gradient Terraces
• Dust Control
6. Protection of Inlets
• Protect inlets, dtywells, catch basins and other stormwater management facilities from sediment, whether or not
facilities are operable, so that stormwater runoff does not enter the conveyance system (both on and off site)
without being treated or filtered to remove sediment;
• Keep roads adjacent to inlets clean; sediment and street wash water shall not be allowed to enter the conveyance
system (both on and offsite) without prior treatment; and,
• Inspect inlets weekly at a minimum and daily during storm eve s. Inlet protection devices shall be cleaned or
removed and replaced before 6 inches of sediment can a ulate.
Suggested BMPs:
• Inlet protection -products manufactured for grate inlet pro tion. Placing silt fence fabric or other drain fabric over
an inlet grate is an unacceptable practice and will n all ed.
7. Runofffrom Construction Sites
• Protect down -gradient properties, waterways, and stormwater facilities from possible impacts due to increased flow
rates, volumes, and velocities of sto ater runoff from the project site that may temporarily occur during
construction;
• Runoff from the construction site through detention/retention storage pond or swales shall be addressed in the
construction sequence. No sediment laden water shall pass through the flow control system and discharge to an
offsite storm conveyance systems;
• Construct stormwater control facilities (detention/retention storage pond or swales) before grading begins. These
facilities shall be operational before the construction of impervious site improvements; and,
• Protect permanent infiltration facilities that are used for flow control during construction.
Suggested BMPs:
• Scheduling
• Sediment Trap
• Temporary Sediment Pond
• Temporary/Permanent Seeding
8. Washout Site for Concrete Trucks and Equipment
• Designate the location of a slurry pit where concrete trucks and equipment can be washed out. Slurry pits are not to
be located in or upstream of a swale, drainage area, stormwater facility or water body, or in an area where a
stormwater facility is existing or proposed.
Suggested BMP:
• Concrete Waste Management
130
9. Material Storage/Stockpile
• Identify locations for storage/stockpile areas, within the proposed ESC plan boundaries, for any soil, earthen and
landscape material that is used or will be used on -site;
• Stockpile materials (such as topsoil) on -site, keeping off roadway and sidewalks; and,
• Maintain on -site, as feasible, items such as gravel and a roll of plastic, for emergency soil stabilization during a heavy
rain event, or for emergency berm construction.
Suggested BMP:
• Stockpile Management
• Material Use
• Material Delivery and Storage
10. Cut and Fill Slopes
• Consider soil type and its erosive properties;
• Divert any off -site stormwater run-on or groundwater away from slopes and disturbed areas with interceptor
dikes, pipes or temporary swales. Off- site stormwater shall be managed separately from stormwater generated
on -site;
• Reduce slope runoff velocities by reducing the continuous length of slope with terracing and diversion, and
roughening the slope surface;
• Place check dams at regular intervals within ditches and trenches that are cut into a slope; and,
• Stabilize soils on slopes, where appropriate.
Suggested BMPs:
• Tem11 -.7 and Perll?anant Caarlina
• Surface Roughening
• Gradient Terraces
• Interceptor Dike an(
• Grass -Lined Channf
• Pipe Slope Drains
• Level Spreader
• Check Dams
• Triangular Silt Dike
11. Stabilization of Temporary Conveyance Channels and Outlets
• Stabilize outlets of all conveyance systems adequately to prevent erosion of outlets, adjacent streambanks, slopes
and downstream reaches.
Suggested BMPs:
• Channel Lining
• Outlet Protection
13. Control of Pollutants Other Than Sediment on Construction Sites
• Control on -site pollutants, such as waste materials and demolition debris, in a way that does not cause contamination
of stormwater or groundwater. Woody debris may be chopped or mulched and spread on -site;
• Cover, contain and protect all chemicals, liquid products, petroleum products, and non -inert wastes present on -
site from vandalism use secondary containment for on -site fueling tanks;
• Conduct maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system
repairs, solvent and de -greasing operations, fuel tank drain down and removal, and other activities that may result
in discharge or spillage of pollutants to the ground or into stormwater runoff using spill prevention measures, such
as drip pans. Clean all contaminated surfaces immediately following any discharge or spill incident If raining,
perform on -site emergency repairs on vehicles or equipment using temporary plastic over and beneath the vehicle;
and,
• Locate pH -modifying sources, such as bulk cement, cement kiln dust, fly ash, new concrete washing and curing
waters, waste streams generated from concrete grinding and cutting, exposed aggregate processes, and concrete
pumping and mixer washout waters, downstream and away from any stormwater facilities or location of proposed
stormwater facilities.
131
Suggested BMPs:
• Concrete Waste Management
• Liquid Waste Management
14. Permanent BMPs
• Include permanent BMPs, if necessary, in the ESC plan to ensure the
successful transition from temporary BMPs to permanent BMPs; and,
• Restore and rehabilitate temporary BMPs that are proposed to remain in place after construction as permanent
BMPs.
15. Maintenance ofBMPs
• Inspect on a regular basis (at a minimum bi-weekly, and daily during/after a runoff producing storm event) and
maintain all ESC BMPs to ensure successful performance of the BMPs. Conduct maintenance and repair in
accordance with individual ESC BMPs outlined in this section; and,
• Remove temporary ESC BMPs within 30 days after they are no longer needed. Permanently stabilize areas that are
disturbed during the removal process.
9.4 STORMWA TER MANAGEMENT PERMIT
9.4.1 PERMIT RESPONSIBILITY
Greater Than or Equal to an Acre
Construction site disturbing greater than or equal to an acre in the City Limits are generally required to follow two sets of
guidelines. The guidelines are from the Montana Department ' n nromnelital Quality (MDEQ) and the City of Kalispell.
In order for a construction project to begin follow the steps belo arding stormwater permits and requirements.
A. MDEQ Requirements for the General Permit for Stormwater charges Associated with Construction Activity
(Permit MTR100000)
1. Develop a Stormwater Pollution Preventi Plan (SWPPP)
• The SWPPP is a document that is d loped to direct and assist operators in identifying sources of potential
pollutants at the construction activity site and Best Management Practices (BMPs) to be used to help ensure
pollutants do not impact receiving surface water through stormwater runoff.
• The SWPPP must contain a narrative description of the project and a drawing of the site with proposed
improvements and BMPs.
• The plan is to be kept on site and available for inspection by MDEQ and the City of Kalispell.
2. Review and submit a Notice of Intent (NOI)
• To obtain the forms necessary to complete the NOI refer to the MPDES General Permit for Stormwater Discharges
Associated with Construction Activity, which can be downloaded from www.deq.state.mt.us.
3. Provide a copy of the NOI, SWPPP, and approval letter to the City of Kalispell Public Works Department a
minimum of 5 days prior to starting land disturbance activities.
4. Post a copy of the complete NOI and SWPPP at the construction site until completion of construction activity.
5. Implement SWPPP prior to beginning land disturbance activity.
6. Inspect and maintain BMPs outlined in Permit MTR100000
7. At the completion of the project submit a Notice of Termination (NOT) following permit requirements. A copy of
the NOT must be submitted to the City of Kalispell Public Works Department.
B. City of Kalispell Stormwater Management Permit Requirements
1. Submit a complete Stormwater Management Permit Application to the City of Kalispell Public Works Department a
minimum of five (5) days prior to land disturbance.
• The permit application must have the following complete forms
1. Stormwater Management Permit Application Form
2. Stormwater Management GREATER Checklist (included in application packet)
3. NOI, SWPPP, Site Map and approval letter from DEQ
132
• The permit fee of $45 for sites greater than or equal to one (1) acre is to be paid at the time the permit application
is submitted.
2. Inspect and Maintain BMPs
• The permittee(s) will be required to perform a site inspection every 14 days and after major storm events to ensure
all BMPs have been constructed and are functioning properly.
• All inspections shall be documented in written form, kept on the project site, and made available for review and
duplication by the City.
3. All changes and notifications submitted to DEQ for the General Permit must also be submitted to the City. This
includes notification of facility contact changes and changes to authorization.
At the completion of the project, submit a copy of the Notice of Termination (NOT) to the City of Kalispell Public Works
Office.
Less Than an Acre
Owners/operators of construction sites less than one (1) acre are required to apply for a City of Kalispell Stormwater
Management Permit (SMP). The SMP requires submittals of an application form and a Stormwater Management Plan in
compliance with the City of Kalispell's Stormwater Management Ordinance 1600.
The Stormwater Management Plan shall contain the following items;
1. A completed Stormwater Management Plan checklist which outlines the project site's Best Management Practices
(BMPs)
2. A short narrative explaining how the permittee(s) will implement BMPs described on the checklist
3. A map of the construction site showing the locations of the BMPs
The Stormwater Management Permit application must be submitted e City of Kalispell Public Works Department a
minimum of five days before construction begins. A fee of $10 f i es than one (1) acre shall be paid at the time the
permit application is submitted.
9.4.2 MAINTENANCE RESPONSIBI
The owner or owner agent is responsible to ensure that BMPs're used, maintained, and repaired so that the performance
standards continue to be met. After all land -disturbing activity is complete and the site has been permanently stabilized,
maintenance and the prevention of erosion and sedimentation is the responsibility of the property owner.
9.4.3 INPECTIONS AND RECORDS
Site Inspections
• The permittee(s) will be required to perform a site inspection every 14 days and after major storm events to ensure
all BMPs have been constructed and are functioning properly.
• All inspections shall be documented in written form, kept on the project site, and made available for review by the
City.
Changes
All changes and notifications submitted to DEQ for the General Permit for Stormwater Discharges Associated with
Construction Activity (Permit MTR100000) must also be submitted to the City. This includes notification of facility
contact changes and changes to authorization.
9.4.4 ENFORCEMENT AND APPEALS PROCESS
If any violation is found, a notice will be issued to the Responsible Party. The notice will state the nature of the alleged
violation(s), the action required to fix the violation(s), and a time limit to fix the violation(s). The City has the authority to
issue a stop work order, clean the public way and bill the owner directly for the actual cost of cleanup plus a $200
administrative fee, and issuing a civil citation. Any person, firm, or corporation violating any of the provisions or terms of
Ordinance #1600 of the City of Kalispell may be subject to penalties as a municipal infraction pursuant of Chapter 1,
Article II of the Kalispell City Code. Each day of continued violation shall constitute a separate, additional offence.
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SECTION 10 - MAINTENANCE, PARCELS,
AND EASEMENTS
10.1 MAINTENANCE
10.1.1 INTRODUCTION
Proper maintenance of stormwater facilities leads to better performance and increases the life of the
facility. Insufficient maintenance of stormwater control facilities can lead to poor performance, shortened
life, increased maintenance and replacement costs, and property damage.
The City of Kalispell maintains the stormwater system structures located within the public road right of way. Drainage
parcels created by public projects will be maintained by the City of Kalispell. The project owner shall provide for the
perpetual maintenance of all elements of the stormwater system located outside the public right of way.
The high -frequency maintenance of vegetated cover, turf grass, and other landscaping within the public right of way and
within easements that accommodate public road runoff is the responsibility of the adjacent property owner. When
applicable, the following maintenance -related items shall be submitted with the Drainage Submittal (refer to Section 3)
for all projects:
• A copy of the conditions, covenants and restrictions (CC&R o e homeowners' association (HOA) in charge of
operating and maintaining all elements of the stormwater st
• A Financial Plan outlining the funding mechanism for th eration, maintenance, and repair of the private
stormwater system, including contingencies; and,
• An Operations and Maintenance (O&M) Manual.
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Appendix l0A outlines facility maintenance re mmendations and frequencies.
10.1.2 APPLICABILITY
All projects that meet the regulatory threshold and at propose drainage facilities or structures shall comply with the Basic
Requirement for operation and maintenance. See Section 2.1 for regulatory threshold descriptions.
10.1.3 HOMEOWNERS' AND PROPERTY OWNERS' ASSOCIATIONS
For privately maintained stormwater systems in residential neighborhoods, a homeowner's association shall be
formed to maintain the facilities located outside of the public right of way.
A draft copy of the CC&Rs for the HOA in charge of operating and maintaining the facilities associated with the stormwater
system shall be submitted as part of the Drainage Submittal review package. The CC&Rs shall summarize the
maintenance and fiscal responsibilities of the HOA and reference the O&M Manual. HOA dues shall provide funding for
the annual operation and maintenance and replacement costs of all facilities associated with the stormwater system.
For commercial/industrial and multi -family residential developments with joint stormwater systems and multiple
owners, a property owners' association (POA) or similar entity such as a business shall be formed, or a reciprocal -use
agreement executed.
Homeowners' associations and property owners' associations are to be non-profit organizations. A standard business
license is not acceptable for this purpose.
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10.1.4 OPERATION AND MAINTENANCE MANUAL
For stormwater systems operated and maintained by a HOA or POA, an O&M Manual is required. The O&M Manual
summarizes the tasks required to ensure the proper operation of all facilities associated with the stormwater system and
must include, as a minimum:
• Description of the entity responsible for the perpetual maintenance of all facilities associated with the stormwater system,
including legal means of successorship;
• A list of contact names, phone numbers, and address of the entity responsible for the perpetual maintenance of all
facilities associated with the stormwater system;
• Description of maintenance tasks to be performed and their frequency;
• An inspection check list to be used for the annual maintenance inspections. Refer to Appendix 10 B for an example
checklist;
• A list of the expected design life and replacement schedule of each component of the stormwater system; and,
• A general site plan (drawn to scale) showing the overall layout of the site, all the facilities associated with the
stormwater system, and their elevations.
10.1.5 MAINTENANCE AGREEMENT
The owner shall be responsible for the operation and maintenance of such measures outline in the Operation and
Maintenance Manual and shall pass such responsibility to any successor owner. Prior to the approval by the Public Works
Department of the stormwater management design plan, each owner shall submit a Maintenance Agreement. The
agreement shall be recorded in the office of the clerk and recorder for Flathead County, Montana.
The stormwater Maintenance Agreement shall be in a form approved he City, and shall, at a minimum meet the
following required elements of the Maintenance Agreement:
• Designate Responsible Party: Designate for the land deve nt th ner, governmental agency, or other legally
established entity (responsible party) which shall be perma y responsible for maintenance of the structural or non-
structural measures required by the Manual.
• Pass Responsibility to Successors: Pass the responsibi 1 y for such maintenance to successors in title.
• Property Description: Provide a legal descrtd
roperty.
• Operation and Maintenance Manual: Ens performance of the maintenance obligation required by the
Operation and Maintenance Manual.
• Signature: The agreement shall be signed designated responsible party.
The agreement shall be recorded in the office of the clerk and recorder for Flathead County, Montana and shall run with the
land.
10.1.6 FINANCIAL PLAN
A Financial Plan is required in order to provide the entity responsible for maintenance with guidance in regard to financial
planning for maintenance and replacement costs. The Financial Plan shall include the following items:
• A list of all stormwater-related facilities and their expected date of replacement and associated costs;
• Sinking fund calculations that take into consideration probable inflation over the life of the infrastructure and
estimates the funds that need to be set aside annually; and,
• A mechanism for initiating and sustaining the sinking fund account demonstrating that perpetual maintenance of
all facilities associated with the stormwater system will be sustained.
10.1.7 FAILURE TO MAINTAIN STORMWATER SYSTEMS
If the required maintenance and repairs are not being performed and inhibit the intended function of the stormwater system
the City may hire a contractor to perform the required maintenance and bill the HOA, POA, or responsible property
owner.
In the event the HOA, POA, or responsible property owner fail to perform the required maintenance and repairs to the
stormwater facility and inhibit the intended function of the stormwater system, a stormwater maintenance district program may
be formed in accordance with §7-12-4102 MCA incorporating all the lots with in a development. The taxes levied within
the maintenance district shall be determined by the Public Works Department with approval by the Kalispell City Council.
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10.1.8 MAINTENANCE ACCESS REQUIREMENTS
An access road is required when the stormwater system facilities/structures are located 8 feet or more from an all
weather drivable surface. When required, maintenance access roads shall meet the following minimum requirements:
• The horizontal alignment of all access roads shall be designed and constructed to accommodate the turning
movements of a Single -Unit Truck (as defined by AASHTO Geometric Design ofHighways and Streets, Exhibit
2-4, 2004 Edition). The minimum outside turning radius shall be 50 feet. The minimum width shall be 12 feet on
straight sections and 15 feet on curves;
• Access roads shall consist of an all weather, drivable surface:
o Reinforced turf is an acceptable surface and shall be installed per manufacturer's specifications and
recommendations. Turf Reinforcement Units: `GRASSPAVE 2', as manufactured by Invisible
Structures, Inc. in an acceptable product or approved equivalent.
o Access road shall not consist of gravel.
• Access roads shall be located within a 20-foot-minimum-width (or as required by the horizontal alignment
requirements) parcel or easement, extending from a public or private road;
• Access roads shall have a maximum grade of 8 percent;
• A paved apron must be provided where access roads connect to paved public roads; and,
The following access road requirements apply only when the City has assumed the responsibility of the maintenance
and operation of the facilities, though it is recommended that access roads for privately maintained facilities also be
designed to meet these criteria:
• If the maintenance access road is longer than 150 feet, a turn -around is required at or near the terminus of the access
road. Turn-arounds are required for long, winding, or steep con ' ' ns, regardless of the length of the drive, where
backing up would otherwise be difficult; and,
• Turn-arounds shall conform to the City's Standards for n Construction.
10.2 PARCELS AND EASEMENTS
Flow control and treatment facilities shall be located within an in idual parcel. Stormwater facilities serving commercial
projects do not generally require parcels or easements unless they serve more than one parcel.
A stormwater facility, as defined for this section, is a natural drainage way, constructed conveyance, swale, or flow control
facility. It is acceptable for other types of drainage systems, such as a pipe, to be in a drainage easement. Other
stormwater drainage systems in a drainage easement, such as pipes, shall not straddle private property lines.
10.2.1 PARCELS
A drainage parcel for access, maintenance, operation, inspection and repair shall be dedicated to the entity in charge of the
maintenance and operation of the stormwater system. A parcel will be dedicated when any of the following situations are
present:
• Facilities associated with a stormwater system serving a residential development are located outside of the public
right of way;
• Drainage ditches located in residential neighborhoods. The limits of the parcel may have to be delineated with a
permanent fence when the ditch is located near property lines; or,
• A natural drainage way is present.
Parcels shall be of sufficient width to provide access to, and maintain, repair or replace elements of the stormwater system
without risking damage to adjacent structures, utilities and normal property improvements, and without incurring additional
costs for shoring or specialized equipment.
10.2.2 EASEMENTS
A drainage easement for access, maintenance, operation, inspection and repair shall be granted to the entity in charge of
the maintenance and operation of the stormwater system. The easement shall grant to the City of Kalispell the right to
ingress/egress over the easement for purposes of inspection, maintenance or repair. If not in a parcel, the following
infrastructure shall be placed within drainage easements:
• Elements of a stormwater system, such as a pipe, located outside the public right of way. Easements for
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stormwater conveyance pipes shall be of sufficient width to allow construction of all improvements, including any
associated site disturbances, and access to maintain, repair or replace the pipe and appurtenances without risking
damage to adjacent structures or incurring additional costs for shoring or special equipment.
o No storm pipe in a drainage easement shall have its centerline closer than 5 feet to a private rear or side
property line.
o The storm drain shall be centered in the easement.
o The minimum drainage easement shall be 20 feet.
o The drainage easement shall not straddle lot lines;
For drainage ditches and natural drainage ways, the easement width shall be wide enough to contain the runoff from a
100-year 24 hour storm event for the contributing stormwater basin. Constructed drainage ditches shall not straddle lot
lines. Natural drainage ways (refer to Section 8.3.4) located on lots larger than 1 acre may be placed in an easement;
and,
Easements for access roads and turnarounds shall be at least 20 feet wide.
Easement documents shall be drafted by the project owner for review by the City Engineer and recorded by the project owner.
Off -Site Easements
When a land action proposes infrastructure outside the property boundaries, an off -site easement shall be recorded
separately from plat documents, with the clerk and recorders reception number placed on the face of the plat The easement
language shall grant the City of Kalispell the right to ingress and egress for purposes of routine or emergency inspection and
maintenance. The following shall be submitted to the City Engineer for review:
• A legal description of the site stamped and signed by a surveyor;
• An exhibit showing the entire easement limits and easement bearings, stamped and signed by a surveyor;
• Proof of ownership for the affected parcel and a list of signat?p and,
• Copy of the draft easement.
For plats and binding site plans, the off -site drainage facility shall�be clearly identified on the plans and operation and
maintenance responsibilities shall be clearly defined prior to acceptance of the project.
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APPENDIX 10A - FACILITY MAINTENANCE
RECOMMENDATIONS
The following are operation and maintenance tasks for Treatment BMPs and Flood Control Facilities and should
be used to create the required Operation and Maintenance Manual. Maintenance of facilities is driven by annual
inspections that evaluate the condition and performance of the stormwater facilities. Based on inspection results,
specific maintenance tasks will be triggered. An annual maintenance inspection form for facilities can be
accessed at CWP website: Hwww.ewp.org/Resource Library/Center Does/SW/peguidance/Tool6.pdf. A more
detailed maintenance inspection form is also available from Appendix B of CWP (2004) and from the City of
Kalispell Public Works Department.
' WET POND MAINTENANCE
First Year Maintenance Operations
Successful establishment of wet ponds requires that certain tasks be undertaken in the first year.
• Initial inspections: For the first six months following construction, the site should be inspected at least twice
after storm events that exceed a 1/2 inch.
• Planting of Benches: The aquatic benches should be planted with emergent wetland species.
• Spot Reseeding: Inspectors should look for bare or eroding areas in the contributing drainage area or around
the pond buffer, and make sure they are immediately stabilized with grass cover.
• Watering: Trees planted in the pond buffer need watering d ing the first growing season, In general,
consider watering every three days for first month, and t weekly during first year (Apr — Oct), depending
on rainfall
Inspections and Routine Maintenance Tasks
Maintenance of wet ponds is driven by annual inspection v ate the condition and performance of the facility
(see Table below).
Suggested Annual Maintenance Inspection Points for Wet Ponds
Activity
Measure sediment accumulation levels in toy
Monitor the growth of wetland plant, tree and shrubs planted. Record species and approximate coverage, and
note presence of any invasive plant species.
Inspect the condition of stormwater inlets to the pond for material damage, erosion or undercutting.
Inspect upstream and downstream banks for evidence of sloughing, animal burrows, boggy areas, woody growth
or gully erosion that may undermine embankment integrity.
Inspect the pond outfall channel for erosion, undercutting, rip -rap displacement, woody growth, etc.
Inspect condition of principal spillway and riser for evidence of spalling, joint failure, leakage, corrosion, etc.
Inspect condition of all trash racks, reverse sloped pipes or flashboard risers for evidence of clogging, leakage,
debris accumulation, etc.
Inspect maintenance access to ensure it is free of woody vegetation and check to see whether valves, manholes or
locks can be opened and operated.
Inspect internal and external pond side slopes for evidence of sparse vegetative cover, erosion or slumping, and
repaired immediately.
Note: For a more detailed maintenance inspection checklist, see Appendix B in CWP (2004) Stormwater Pond
and Wetland Maintenance Guidebook.
Maintenance is needed so stormwater ponds continue to operate as designed on a long-term basis. Wet ponds normally
have less routine maintenance requirements than other stormwater treatment options. Stormwater pond maintenance
activities range in terms of the level of effort and expertise required to perform them. Routine stormwater pond
maintenance, such as mowing and removing debris or trash, is needed several times each year (See Table below).
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More significant maintenance such as removing accumulated sediment is needed less frequently, but requires more
skilled labor and special equipment. Inspection and repair of critical structural features such as embankments and
risers, needs to be performed by a qualified professional (e.g., a structural engineer) that has experience in the
construction, inspection, and repair of these features.
The maintenance plan should clearly outline how vegetation in the pond and its buffer will be managed or harvested in
the future. Periodic mowing of the stormwater buffer is only required along maintenance rights -of -way and the
embankment. The remaining buffer can be managed as a meadow (mowing every other year) or forest. The
maintenance plan should schedule a shoreline cleanup at least once a year to remove trash and floatables.
Typical Wet Pond Maintenance Tasks and Frequency
Maintenance Items
Frequency
•
Pond buffer reinforcement plantings and planting of aquatic
One time - After First Year
benches.
•
Mowing — twice a year.
Quarterly or After Major Storms
•
Remove debris and blockages.
(>1 inch)
•
Repair undercut, eroded, and bare soil areas.
•
Shoreline cleanups to remove trash, debris and floatables.
•
Full maintenance inspection.
Annual
•
Open up riser to access valves.
•
Repair broken mechanical components if needed.
•
Forebay Sediment Removal.
5-7 years
•
Repair pipes, riser and spillway where needed.
1 5-25 years
qmp� & INFILTRATION MAINTENANCE
Maintenance Inspections
Annual site inspections are critical to the performance anriielt�raytionof infiltration practices, particularly for small-
scale and conventional infiltration practices. Mai cepractices is driven by annual inspections that
evaluate the condition and performance of the pra � below).
Ongoing Maintenance
Effective long-term operation of infiltration pr s requires a dedicated and routine maintenance inspection
schedule with clear guidelines and schedules, as shown in the Table below. Where possible, facility maintenance
should be integrated into routine landscaping maintenance tasks.
PointsSuggested Annual Maintenance Inspection
Activity
The drawdown rate should be measured at the observation well for three days following a storm event in excess
of 0.5 inch in depth. If standing water is still observed in the well after three days, this is a clear sign that that
clogging is a problem.
Check inlets, pretreatment cells and any flow diversion structures for sediment buildup and structural damage.
Note if any sediment needs to be removed.
Inspect the condition of the observation well and make sure it is still capped.
Check that no vegetation forms an overhead canopy that may drop leaf litter, fruits and other materials that could
clog the device.
Evaluate the vegetative quality of the adjacent grass buffer and do spot reseeding if cover is less than 90%.
Generally inspect the upland CDA for any controllable sources of sediment or erosion.
Look for weedy growth on rock surface that might indicate sediment deposition or clogging.
Inspect maintenance access to ensure it is free of woody vegetation and check to see whether valves, manholes or
locks can be opened and operated.
Inspect internal and external infiltration side slopes for evidence of sparse vegetative cover, erosion or slumping,
and repaired immediately.
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Typical Maintenance Activities for Infiltration Practices
Activity
Schedule
•
Replace pea gravel/topsoil and top surface filter fabric (when
As needed
clogged).
•
Mow grass filter strips as necessary and remove clippings.
•
Ensure that contributing area, practice and inlets are clear of
Quarterly
debris.
•
Ensure that the contributing area is stabilized.
•
Remove sediment and oil/grease from pretreatment devices,
as well as overflow structures.
•
Repair undercut and eroded areas at inflow and outflow
structures.
•
Check observation wells following 3 days of dry weather.
Semi-annual Inspection
Failure to percolate within this time period indicates clogging.
•
Inspect pretreatment devices and diversion structures for
sediment build-up and structural damage.
•
Remove trees that start to grow in the vicinity of the trench.
•
Clean out accumulated sediments from the pretreatment cell
Annually
POND MAINTENANCE
Maintenance Inspections
Maintenance of ED ponds is driven by annual inspections that evaluate condition and performance of the facility
(see Table below). Based on inspection results, specific maintenance tas s will be triggered.
Common Maintenance Issues
Ponds are prone to a high clogging risk at the h
least twice a year after initial construction. The
manage vegetative growth. The bottom of c
over.
These aspects of pond plumbing should be inspected at
ging water levels in ponds make it difficult to mow or
soggy, and water -loving trees such as willows may take
The maintenance plan should clearly outline hoNf vegetation in the pond and its buffer will be managed or harvested in
the future. Periodic mowing of the stormwater buffer is only required along maintenance rights -of -way and the
embankment. The remaining buffer can be managed as a meadow (mowing every other year) or forest. The
maintenance plan should schedule a shoreline cleanup at least once a year to remove trash and floatables that tend to
accumulate in the forebay and on the bottom of ponds.
Frequent sediment removal from the forebay or sump area is essential to maintain the function and performance of a
pond. Maintenance plans should schedule cleanouts every 5-7 years, or when inspections indicate that 50% of forebay
or smp area capacity has been lost.
Suggested Annual Maintenance Inspection
Activity
Measure sediment accumulation levels in forebay.
Monitor the growth of wetlands, trees and shrubs planted. Record species and approximate coverage, and note
presence of any invasive plant species.
Inspect the condition of stormwater inlets to the pond for material damage, erosion or undercutting.
Inspect upstream and downstream banks for evidence of sloughing, animal burrows, boggy areas, woody growth
or gully erosion that may undermine embankment integrity.
Inspect pond outfall channel for erosion, undercutting, rip -rap displacement, woody growth, etc.
Inspect condition of principal spillway and riser for evidence of spalling, joint failure, leakage, corrosion, etc.
Inspect condition of all trash racks, reverse sloped pipes or flashboard risers for evidence of clogging, leakage,
debris accumulation, etc.
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Inspect maintenance access to ensure it is free of woody vegetation and check to see whether valves, manholes or
locks can be opened and operated.
Inspect internal and external pond side slopes for evidence of sparse vegetative cover, erosion or slumping, and
Note: For a more detailed maintenance inspection checklist, see Appendix B in CWP(2004) Stormwater Pond
and Wetland Maintenance Guidebook.
—'"= DRY SWALE MAINTENANCE _
Maintenance Inspections
Inspections are used to trigger maintenance operations such as sediment removal, spot revegetation and inlet
stabilization. Several key maintenance inspection points are detailed in the Table below. Ideally, inspections should be
conducted in the spring of each year.
Suggested for Dry Swales
Activity
Add reinforcement planting to maintain 95% turf cover on vegetation density. Reseed any salt killed vegetation.
Remove any accumulated sand or sediment deposits on the filter bed surface or in pretreatment cells.
Inspect upstream and downstream of check dams for evidence of undercutting or erosion, and remove and trash
or blockages at weep holes.
Examine filter beds for evidence of braiding, excessive ponding or dead grass.
Check inflow points for clogging and remove any sediment.
Inspect side slopes and grass filter strips for evidence of any Zo lly erosion and repair.
Look for anv bare soil or sediment sources in the contribuAg kainagrarea and stabilize.
Routine Maintenance and Operation
Once established, dry swales have minimal maintenance need:oVtside of the spring clean up, regular mowing and
pruning and management of trees and shrubs. The surface o e filter bed can become clogged with fine sediment
over time, but this can be alleviated through e aeratio r deep tilling of the filter bed. Additional effort may be
needed to repair check dams, stabilize inle oint and rmove deposited sediment from pretreatment cells.
r ]W' BIOSWALE AND GRASS CHANNEL MAINTENANCE
Maintenance Inspections
Annual inspections are used to trigger maintenance operations such as sediment removal, spot
revegetation and inlet stabilization. Several key maintenance inspection points are detailed in the Table
below. Ideally, inspections should be conducted in the spring of each year.
Ongoing Maintenance
Once established, bioswales and grass channels have minimal maintenance needs outside of the Spring
clean up, regular mowing, repair of check dams and other measures to maintain the hydraulic
efficiency of the channel and a dense, healthy grass cover.
Suggested Spring Maintenance Inspections/Cleanups for Grass Channels
Activity
Add reinforcement planting to maintain 90% turf cover. Reseed any salt killed vegetation.
Remove any accumulated sand or sediment deposits behind check dams.
Inspect upstream and downstream of check dams for evidence of undercutting or erosion, and remove and trash
or blockages at weep holes.
Examine channel bottom for evidence of erosion, braiding, excessive ponding or dead grass.
Check inflow points for clogging and remove any sediment.
Inspect side slopes and grass filter strips for evidence of any rill or gully erosion and repair.
141
Look for any bare soil or sediment sources in the contributing drainage area and stabilize immediately.
r BIORETENTION MAINTENANCE
First Year Maintenance Operations
Successful establishment of bioretention areas requires certain tasks be undertaken in the first year.
• Initial inspections: For the first six months following construction, the site should be inspected at least twice
after storm events that exceed a half- inch
• Spot Reseeding: Inspectors should look for bare or eroding areas in the contributing drainage area or around
the bioretention area, and make sure they are immediately stabilized with grass cover
• Fertilization: one-time, spot fertilization for initial plantings
• Watering: Once a week during the first two months, and then as needed during first growing season (Apr —
Oct), depending on rainfall
• Remove and replace dead plants. Since up to ten percent of plant stock may die off in the first year,
construction contracts should include a care and replacement warranty to ensure vegetation is properly
established and survives during the first growing season following construction. The typical thresholds for
replacement are 85% survival of plant material and 100% survival of trees.
Maintenance Inspections
It is highly recommended that a spring maintenance inspection and cleanup be conducted at each bioretention area.
The Table below presents some of the key maintenance problems.
Suggested Spring Maintenance Inspections for Bioretention
Activity
Check to see if 90% mulch + vegetative cover has been achieved in the bed, and measure depth of remaining
mulch.
Check for sediment buildup at curb cuts, gravel diaphragms oVKavement edges that prevent flow from getting
into the bed.
Check for any winter or salt -killed vegetation and replace with hardier species.
Note presence of accumulated sand, sedi ent and trash in pretreatment cell or filter beds and remove.
Inspect bioretention side slopes and grass filter stps for evidence of any rill or gully erosion and repair.
Check bioretention bed for evidence of mulchlWotation, excessive ponding, dead plants or concentrated flows
and take appropriate remedial action.
Check inflow points for clogging and remove any sediment.
Look for any bare soil or sediment sources in the contributing drainage area and stabilize immediately.
Routine and Non -Routine Maintenance Tasks
Maintenance of bioretention areas should be integrated into routine landscaping maintenance tasks. If landscaping
contractors will be expected to perform maintenance, their contracts should contain specifics on unique bioretention
landscaping needs, such as maintaining elevation differences needed for ponding, proper mulching, sediment and trash
removal, and limited use of fertilizers and pesticides. A customized maintenance schedule must be prepared for each
bioretention facility, since the maintenance tasks will differ depending on the scale of bioretention, the landscaping
template chosen, and the nature of surface cover. A generalized summary of common maintenance tasks and their
frequency is provided in the Table below.
Suggested Annual Maintenance Activities
Maintenance Tasks
for Bioretention
Frequency
• Spring inspection and cleanup.
Annual
• Add reinforcement planting to maintain desired vegetation
density.
As needed
• Spot weeding, erosion repair, trash removal, and mulch
raking.
Twice during growing season
• Sediment removal in pretreatment cells and inflow points.
Once every two to three years
• Mowing of grass filter strips and bioretention turf cover.
At least four times a year
14
• Remove invasive plants using recommended control
methods.
As needed
• Supplement mulch to maintain a 3 inch layer.
Annual
• Replace mulch layer.
Every three years
• Prune trees and shrubs.
Annual
• Stabilize contributing drainage area to prevent erosion.
When needed
The most common non -routine maintenance problem involves standing water. If water remains on the surface for more
than 48 hours after a storm, adjustments to the grading may be needed or underdrain repairs may be needed. The
surface of the filter bed should also be checked for accumulated sediment. Core aeration or deep tilling may relieve the
problem.
143
APPENDIX IOB - FACILITY INSPECTION
CHECKLIST
Stormwater Management Facility Inspection and Maintenance Log (Sample)
Property Address:
Inspection Date:
Inspection Time:
Inspected By:
Date and Time of Last Rainfall:
Type of Stormwater Management Facility:
Location of Facility on Site (in relation to buildings or other structures):
Water levels and observation (Oil sheen, Smell, Turbidity, etc.):
Sediment accumulation and record of sediment removal:
Condition of Vegetation (Height, survival rates, invasion species present, etc.) and record of replacement and
management (mowing, weeding etc.)
Condition of physical properties such as inlet , outlets, piping, fences, irrigation facilities, and side slopes.
Record damaged items and replacement activities:
Presence of insects or rodents. Record control activities:
Identify safety hazards present. Record resolution activities:
144
ABBREVIATIONS AND ACRONYMS
• AASHTO—American Association of State Highway and Transportation Officials
• APWA—American Public Works Association
• ARC —Antecedent Runoff Condition
• ASTM—American Society for Testing and Materials
• BMP—Best Management Practice
• CC&R—Conditions, Covenants and Restrictions
• cfs—Cubic Feet per Second
• CMP—Corrugated Metal Pipe
• CN—Curve Number
• ESC—Erosion & Sediment Control
• FEMA—Federal Emergency Management Agency
• FHWA—Federal Highway Administration
• FIRM —Flood Insurance Rate Map
• FS—Factor of Safety
• GW—Grate Width
• GSC—Geotechnical Site Charact(
• HDPE—High-Density Polyethylc
• HGL—Hydraulic Grade Line
• HOA—Homeowner' s Associatior
• IBC —International Building Codi
• Manual —City of Kalispell StormN
• MDT —Montana Department of Transportation
• NDW—Natural Drainage Ways
• NOAA—National Oceanic and Atmospheric Administration
• NPDES—National Pollutant Discharge Elimination System
• NRCS
—Natural Resources Conservation Service
• O&M
—Operation and Maintenance
• PAM—Polyacrylamide
• POA—Property
Owners Association
• SCS—Soil Conservation Service
• sf—Square
Feet
• TMDL—Total
Maximum Daily Load
• TPH—Total Petroleum Hydrocarbons
• TSS—Total Suspended Solids
• USGS—United States Geological Survey
• WSDOT—Washington State Department of Transportation
145
REFERENCES
1. AASHTO Geometric Design of Highways and Streets, Exhibit 2-4, 2004 Edition [Section 10.1.6]
2. Open Channel Hydraulics, 1959, Ven Te Chow (1959) [Tables 5-4, 8-4]
3. Engman (1983) [Tables 5-3 and 5-4]
4. FHWA, Hydraulic Engineering Circular No. 22, Second Edition [Table 8-6, Section 8.6.2]
5. Florida Department of Transportation Drainage Manual (1986) [Tables 5-3 and 5-4]
6. Handbook of Applied Hydrology, (Chow, Ven Te, 1964) [Section 5.4]
7. Handbook of Hydraulics, by Brater and King
8. Infiltration Rate and Soil Classification Correlation, File No. 0188-082-00, May 28, 2004; prepared by
GeoEngineers, Budinger & Associates, Inc., and Cummings Geotechnology, Inc. [Chapter 4 Appendices]
9. King County Surface Water Design Manual, 1998. [Figures 6-2, 6-3, 7.2, 7.3, 7-8, and 7.4 ]
10. Length of an apron (La) is determined using the following empirical relationships that were developed for the U.S.
Environmental Protection Agency, ASCE (1992) [Section 8.3.2]
11. NOAA Atlas 2, Volume IX, 1973 [Sections 5.3.8 and Table 5-5]
12. Open -Channel Hydraulics by French. [Section 8.4]
13. WSDOT Standard Plans, July 2001 [Section 8.3]
14. SCS National Engineering Handbook (1985). [Section 5.3.2 and Table 5-2]
15. Section 3-8 of the U.S. Bureau of Reclamation Drainage Manual. [Chapter 4 Appendices]
16. MTD Hydrology Manual [figure 5-1, Section 5.3.10, Section 5.5, Table 5-6, 5-7, 5-8]
17. Spokane Regional Stormwater Manual, April 2008 [Everywhe ]
18. Soil Conservation Service's Technical Release No. 55 , (21 I-TR-55, Second Ed., June 1986). [Section 5.3.3
and Table 5-1]
19. Special Committee on Irrigation Research, American Society of it Engineers, 1926. [Table 8-1]
20. Standard Plans jointly published by WSDOT and APWA (M2 1-01) [Section 8.6.1]
21. Stormwater Management Manual for Eastern Washington [Section 6]
22. WSDOT Highway Runoff Manual (2004) [Tables 5-3 and 5-4]
23. City of Kalispell 2008 Storm Water Facility Plan Update [Section 8]
24. City of Kalispell Stormwater Quality Management Plan [Section 6]
25. Knox County Tennessee Stormwater Management Manual [Section 6]
26. Georgia Stormwater Management Manual [Section 6]
27. Montana Natural Resource Conservationn[Section 61
28. Baywide Stormwater Design Specification [Section 6 and 10]
146
CHAPTER IV
CONSTRUCTION STANDARDS
CS-01 Proiect Requirements
Contractors installing water, sanitary sewer, storm sewer and roadways or any other public
improvements shall be subject to the following requirements:
Construction Contractor Registration. Any Contractor working within an existing Public Right -of -
Way or Easement shall be registered with the Montana Department of Labor and Industry,
Employment Relations Division.
Insurance and Bonding. Insurance and bonding shall be in accordance with Section GP-07 and GP-08,
as applicable.
Pre -Construction Conference. Prior to any construction start a preconstruction conference shall be
held. The Public Works Department, the Project Engineer, the Owner, and the Contractor shall be
represented. Items to be discussed at the pre -construction conference are construction schedule, shop
drawing submittals, utility installation, materials testing, uality control, maintenance bond, and other
items as may be necessary.
Shop Drawing Submittal. If the proposed items to be installed differ from the approved plans and
specifications, shop drawings shall be submitted for review not later than ten (10) business days prior
to the proposed installation.
CS-02 Construction Standards.
All water, sanitary sewer, storm drain and roadway systems, or any other construction of
infrastructure within the public right-of-way or easement, shall be constructed, inspected, and tested in
accordance with the current edition of The Montana Public Works Standard Specifications and the
Standards for Design & Construction of the City of Kalispell and other standards referenced elsewhere
in this document. With respect to the design and/or construction of public facilities, any conflict(s) or
difference(s) between the Montana Public Works Standard Specifications, the City of Kalispell
Subdivision Regulations, and the City of Kalispell Standards for Design and Construction shall be
resolved in favor of the City of Kalispell Standards for Design and Construction.
Underground Utilities. All underground electrical, gas, phone, and TV cable lines must be installed at
least three (3) feet horizontally from water, sanitary sewer and storm sewer mains and services.
CS-03 Construction Inspection, Testing, and Quality Control
A Professional Engineer, or his designated representative, shall provide construction inspection and
testing as required. Inspection and testing shall be in accordance with the current edition of the
Montana Public Works Standard Specifications and the Standards for Design and Construction
Kalispell, MT. The following quality control procedures will apply to all utility and roadway
construction projects. The City reserves the right to conduct independent quality control testing at the
147
City's expense during any phase of the construction. The Contractor shall bear the expense of failed
tests and the expense of bringing the material into conformance with the required specifications.
1. All water main valves and fittings, fire hydrants, sewer manholes, wet wells and sewer/water
main crossings shall be inspected and approved by the Professional Engineer, or his designated
representative, prior to backfilling.
2. A Professional Engineer, or his designated representative, shall be present for all tests required
in Section 02660 and Section 02730 of the Montana Public Works Standard Specifications. A
written record of all test results shall be submitted to the Public Works Department.
3. A Professional Engineer, or his designated representative, shall provide the Public Works
Department with photocopies of daily inspection reports, including Proctors and compaction
test results for all projects. These reports shall be submitted on a weekly basis.
The following minimum compaction testing procedures shall apply to all utility and roadway
construction projects. An independent accredited testing laboratory shall be retained to provide the
following tests and frequency. Random longitudinal test locations are required. The following are
minimum compaction test requirements. The Professional Engineer, or his designated representative,
may require additional tests. For projects containing les than 300 linear feet of improvements, a
minimum of one compaction test for each improvemen 11 be required for the improvements listed
below.
1. Utility Trenches and Underground Structures:
For trenches up to eight (8) feet in depth, density t sts shall be taken at twelve (12) inches above the
pipe at one-half the trench depth and at the surface. For trenches greater than eight (8) feet in depth,
density tests shall be taken at twelve (12) inches above the pipe, at one-third and two -third the trench
depth levels, and at the surface. ly
The minimum density shall be 95% Standard Proctor, ± 3% optimum moisture.
Horizontal Frequency:
1. Utility Mains — One set of tests per 300 feet.
2. Service Lines — One set of tests per three (3) services per utility type.
3. Open Pit — Minimum of one test (Open Pit — at each manhole, water valve, storm inlet, curb
inlet, vault, etc.)
Each test location shall be separated horizontally from a prior test location.
2. Street sub grade:
All sub -base: 95% Standard Proctor, ± 3% optimum moisture. One random density test, every 300
linear feet of street.
All crushed gravel base: 95% Standard Proctor, ± 3% optimum moisture. One random density test,
every 300 linear feet of street.
148
Television Inspection. The City of Kalispell reserves the right to inspect all underground utility
systems by the use of a television camera prior to final acceptance. The City will perform the initial
inspection at no cost to the contractor. If the City is required to clean debris, gravel, etc. from the line
in order to perform the TV inspection, the costs for the cleaning services will be billed to the
Contractor. Any deficiencies found by the initial TV inspection shall be corrected by the contractor.
The cost of the additional TV testing required to ensure the deficiencies have been corrected will be
billed to the Contractor.
CS-04 Record Drawings and Proiect Acceptance.
Upon project completion and before final acceptance, a Professional Engineer shall certify to the City
that the construction of the public utilities and roadways meets the requirements of the approved
construction documents. The Engineer shall submit one set of record drawings (hard copy and DWG
digital format) and one set of the test results as required under Section CS-03 of these standards to the
Public Works Department. The City will not accept the project until record drawings and test results
have been approved by the City Engineer. The two year maintenance guarantee period will begin on
the date stated in accordance with Section GP-08 Maintenance Bond for New Infrastructure. The
Project Engineer shall provide quantities and unit costs of all City owned infrastructure.
CS-05 Two Year Guarantee Inspection.
The Project Engineer, or his designated representative, shall conduct a two year guarantee inspection,
to be attended by a representative from the Public Works Department. The inspection shall take place
not less than ninety (90) days prior to the expiration date of the Maintenance Bond. The maintenance
bond will be released when all deficienc' e been corrected to the satisfaction of the City
Engineer.
The City Engineer, the Project Engineer, his designated representative, shall notify the Principal as
listed in the Maintenance Bond of any work found to be not in accordance with the approved
construction documents. The Principal shall restore the work to meet the requirements of the approved
construction documents prior to the release of the Maintenance Bond. The City expressly reserves the
right to draft the Maintenance bond for repairs not completed by the Owner, Developer, or Contractor
within thirty calendar days of being advised that repairs are required.
CS-06 Boulevard Landscaping.
The Contractor shall place a minimum of 4" of topsoil within the boulevard. The finished surface of
the topsoil shall provide adequate drainage from the top of the sidewalk to the top of the curb. Topsoil
shall be fertile, natural loam surface soil, free of clay, weeds, roots or stones larger than one inch in
any dimension. Boulevard landscaping shall be placed in accordance with the Kalispell Street Tree
Ordinance and a plan approved by the Kalispell Parks and Recreation Department.
149
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CHAPTER V
STANDARD DRAWINGS
0l
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❑F
0 4" ASPHALT -SHALL BE TYPE B (ASPHALT CONCRETE PAVEMENT
SURFACE COURSE TYPE B SHALL BE ACCOMPLISHED IN ACCORDANCE
WITH SECTION 02514 PART 1 THROUGH PART 3 OF THE 2006 ADDENDUM
TO THE MONTANA PUBLIC WORKS STANDARD SPECIFICATIONS, FIFTH
EDITION, MARCH 2O03. SEE DS-4 ASPHALT SURFACING, REGRADING
PAVEMENT AND MATERIAL TESTING REQUIREMENTS.
Q 5" CRUSHED GRAVEL BASE, -314" DIAMETER@95% DENSITY Q 3%
OPTIMUM MOISTURE) PER AASHTO T-99
Q 15" SELECT SUB-BASE@950k DENSITY L 3% OPTIMUM MOISTURE] PER
AASHTO T-991.
1, THICKNESSES OF ASPHALT, CRUSHED GRAVEL AND SUS -BASE SHALL
BE AS SHOWN, UNLESS AN ALTERNATE DESIGN IS APPROVED. THE FINAL
STREET DESIGN SHALL BE APPROVED BY THE CITY ENGINEER PRIOR TO
START OF CONSTRUCTION.
2. THE WIDTH OF THE RIGHT-OF-WAY MAY BE INCREASED DUE TO UTILITIES,
OR OTHER REQUIREMENTS.
3. THE MAXIMUM GRADE SHALL BE 8%/
4. ON STREET PARKING GOVERNED BY CITY OF KALISPELL SUBDIVISION
REGULATIONS.
I1TII ITY NOTF,
ALL NEW UTILITIES SHALL BE PLACED UNDERGROUND. EXCEPT FOR SEWER AND WATER,
UNDERGROUND UTILITIES, IF PLACED IN THE STREET RIGHT-OF-WAY OR EASEMENT, SHALL BE
LOCATED BETWEEN THE BACK OF THE SIDEWALK AND THE EASEMENT LINE. NO UNDERGROUND
UTILITIES SHALL BE PLACED IN THE BOULEVARD BETWEEN THE BACK OF CURB AND SIDEWALK.
REV! 71241W
CONSTRUCTIONCITY OFKALISPELDARDS I COLLECTOR STREET I SD-1
150
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SOULEVARD 1 BOULEVARD
3
(Dd" ASPHALT - SHALL BE TYPE B (ASPHALT CONCRETE PAVEMENT
SURFACE COURSE TYPE B SHALL BE ACCOMPLISHED IN
ACCORDANCE WITH SECTION 02510 PART 1 THROUGH PART 3 OF
THE 2006 ADDENDUM TO THE MONTANA PUBLIC WORKS
STANDARD SPECIFICATIONS, FIFTH EDITION, MARCH 2O03.SEE D5-4
ASPHALT SURFACING, REGRADING PAVEMENT AND MATFRIAL
TESTING REQUIREMENTS.
Q B" CRUSHED GRAVEL BASE, -314" DIAMETER@95%
DENSITY ( 3% OPTIMUM MOISTURE) PER AASHTO T-99.
(J)9' SELECT SUB-BASE@95% DENSITY (+ 3% OPTIMUM
MOISTURE) PER AASHTO T-99
1, THICKNESSES OF ASPHALT, CRUSHED GRAVEL AND SUB -BASE SHALL
BE AS SHOWN, UNLESS AN ALTERNATE DESIGN IS APPROVED. THE
FINAL STREET DESIGN SHALL BE APPROVED BY THE CITY ENGINEER
PRIOR TO START OF CONSTRUCTION.
2. THE WIDTH OF THE RIGHT-OF-WAY MAY BE INCREASED DUE TO
UTILITIES, OR OTHER REQUIREMENTS.
3. THE MAXIMUM GRACE SHALL BE 8%.
d_ ON STREET PARKING GOVERNED BY CITY OF KALISPELL
SUBDIVISION REGULATIONS.
UTILITY NOTE:
ALL NEW UTILITIES SHALL BE PLACED UNDERGROUND, EXCEPT FOR SEWER AND WATER,
UNDERGROUND UTILITIES, IF PLACED IN THE STREET RIGHT-OF-WAY OR EASEMENT, SHALL BE
LOCATED BETWEEN THE BACK OF THE SIDEWALK AND THE EASEMENT LINE. NO UNDERGROUND
UTILITIES SHALL BE PLACED IN THE BOULEVARD BETWEEN THE BACK OF CURB AND SIDEWALK.
REV7/24/09
CONSTRUCTION STANDARDS
CITY OF KALISPELL
LOCAL STREET
SD-2
151
4" ASPHALT - SHALL BE TYPE B (ASPHALT CONCRETE PAVEMENT
SURFACE COURSE TYPE B SHALL BE ACCOMPLISHED IN
ACCORDANCE WITH SECTION 02510 PART 1 THROUGH PART 3 OF
THE 2006 ADDENDUM TO THE MONTANA PUBLIC WORKS
STANDARD SPECIFICATIONS, FIFTH EDITION, MARCH 2O03. SEE
DS-4 ASPHALT SURFACING, REGRADING PAVEMENT AND MATERIAL
TESTING REQUIREMENTS.
6- CRUSHED GRAVEL BASE, -314" 0IAMETER*95% DENSITY
(* 3% OPTIMUM MOISTURE) PER AASHTO T-99
9" SELECT SUB-BASE@95% DENSITYL+3%.OPTIMUM
MOISTURE) PER AASHTn T-99
04" CRUSHED GRAVEL SHOULDER, -314- DIAMETER@95%
DENSITY(± 3% OPTIMUM MOISTURE) PER AA5HTO T-99
1. THIS CROSSSECTIpN MAYBE USED ONLY WHEN THE AREA ADJACENT
TO THE PROPOSED DEVELOPMENT DOES NOT HAVE CURBING OR
ESTABLISHED STORM DRAINAGE SYSTEMS. THIS CROSS-SEC-PON MUST
BE APPROVED BY THE CITY COUNCIL PRIOR TO INCORPORATING INTO
THE DRAWINGS.
2. THICKNESSES OF ASPHALT, CRUSHED GRAVEL AND SUB -BASE SRALL
BE AS SHOWN, UNLESS AN ALTERNATE DESIGN IS APPROVED. THE
FINAL STREET DESIGN SHALL BE APPROVED BY THE CITY ENGINEER
PRIOR TO START OF CONSTRUCTION-
3. THE WIDTH OF THE PAVEMENT WILL DEPEND ON LOCAL
CONDITIONS SUCH AS WIDTHS OF EXISTING STREETS IN
THE AREA, ANTICIPATED TRAFFIC VOLUME, FUTURE
EXTENSION$, ETC-
4. THE WIDTH OF THE RIGHT-OF-WAY MAY BE INCREASED DUE TO
UTILITIES, OR OTHER REQUIREMENTS,
5. ON STREET PARKING GOVERNED BY CITY OF KALISPELL
SUBDIVISION REGULATIONS.
6- THE MAXIMUM GRADE SHALL BE 5%.
REV: 7124109
CONSTRUCTION STANDARDS
CITY OF KALISPELL RURAL ROAD SD-3
152
210
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25 MAX- 2°4 MAX
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(iD 4- ASPHALT - SHALL BE TYPE B {ASPHALT CONCRETE PAVEMENT SURFACE COURSE TYPE B SHALL BE
ACCOMPLISHED IN ACCORDANCE WITH SECTION 02510 PART 1 THROUGH PART 3 OF THE 2006
ADDENDUM TO THE MGNTANA PUBLIC WORKS STANDARD SPECIFICATIONS, FIFTH EDITION, MARCH
2003. SEE IDS-4 ASPHALT SURFACING. REGRADING PAVEMENT AND MATERIAL TESTING
REQUIREMENTS.
t } 6" CRUSHED GRAVEL BASE, - 14" DIAMETER495% DENSITY Lt 3% OPTIMUM MOISTURE)
PER AASHTO T-99
RESIDENTIAL: 9" SELECT SUB-BASE@95% DENSITY Lt 3% OPTIMUM MOISTURE) PER
AA8HT4 T-99
RESIDENTIAL ALLEY
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10' 10'
2% MAX 2% MAX
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( 4• ASPHALT - SHALL BE TYPE B {ASPHALT CONCRETE PAVEMENT SURFACE
COURSE TYPE B SHALL BE ACCOMPLISHED IN ACCORDANCE SMITH SECTION
02510 FART 1 THRDUGH PART 3 OF THE 2006 ADDENDUM TO THE MONTANA
PUBLIC WORKS STANDARD SPECIFICATIONS, FIFTH EDITION, MARCH 2O03.
SEE DS-4ASPHALT SURFACING. REGRADING PAVEMENT AND MATERIAL TESTING
REQUIREMENTS.
6' CRUSHED GRAVEL BASE, -314- DIAMETER@95% DENSITY L+ 3% OPTIMUM
MOISTURE) PER AASHTO T-99
} BUSINESS: 15' SELECT SUB -BASE[ 95% DENSITY (+ 3% OPTIMUM MOISTURE)
PER AASHTD T-99
BUSINESS DISTRICT ALLEY REV: 7124109
URBAN DESIGN STANDARD ALLEY SD-4
153
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1. 1/2" EXPANSION JOINT MATERIAL SHALL BE PLACED AT EACH POINT OF
CURVATURE AND POINT OF TANGENCY.
2. CONTRACTION ]DINTS SHALL BE PLACED AT EVERY 15' OF CURB LENGTH
AND SHALL HAVE A MINIMUM DEPTH OF 3/4" AND A MINIMUM WIDTH OF
1/8". CONTRACTION JOINTS SHALL BE CONSTRUCTED BY SAWING OR
SCORING. A TOOL SHALL BE USED WHICH WILL LEAVE CORNERS ROUNDED
AND DESTROY AGGREGATE INTERLOCK FOR THE SPECIFIED MINIMUM
DEPTH.
3. EXPOSED EDGES SHALL BE FINISHED TO A RADIUS OF 1/4
4. CONCRETE SHALL BE M-4000 WITH 3/4" MAXIMUM AGGREGATE, MINIMUM
28-DAY STRENGTH OF 4000 PSI, 6%❑+ 1 1/2%❑ AIR ENTRAINMENT, AND
MAXIMUM SLUMP OF 4".
S. INDIVIDUAL CONTRACTORS FORMS MAY VARY SLIGHTLY FROM THIS
PATTERN. PATTERNS DIFFERING MATERIALLY FROM THE ABOVE
DIMENSIONS SHALL BE SUBMITTED TO THE CITY FOR REVIEW.
6. FOUR INCHES OF CRUSHED GRAVEL BASE MATERIAL, -3/4" DIAMETER
IS REQUIRED FOR THE CURB AND GUTTER FOUNDATION. THE BASE
MATERIAL SHALL BE COMPACTED TO 95% DENSITY L 3% OPTIMUM
MOISTURE) PER AASHTO T-99.
REV: 1 a131108
CONSTRUCTION STANDARDS
CITY OF KALISPELL CURB AND GUTTER SD-5
154
Ri.
4
WA14MON JUNTa' Ma► AT EACHPONTOF
CURVATURE ANDPOINT OF a
2. CONTRACTION JOINTS• 1 AT EVERYOF CURB LENGTH
f SHALL HAVE A MINIMUF4 DEPTH OF OF A MMUM11 OF
CONTRACTION JOINTSCONSTRUCTED BY SAWINGOR
SCORING.•• USED WHICH WILLO •• ►:►
/ DESMY AGGREGATE INTERLOCKFOR THE SPECIFIED MD[[MUM
• '
3. SSM EDGES SHALL BE FINISHED TO A RADIUS OF 11,r.
4. CONCRETE • 111 WITH 3/411 MAMUM AGGREGATE,III
28-DAY STRENGTH OF III "i ENIMMENT, AND
MAXMUM SLUMP OF
S. INDPMK CONTRACTORS FORM MAY VARY SLlGHTLYFROM I.
PATTERN. PATTERNS DUTERING MATERIALLY FROM THE ABOVE
DIMENSIONS SHALL BE SUBMITTED TOTHE CITY FOR REVIEW.
FOUR INCHES OF CRUSHED GRAVEL a' DIAMETER
IS REQUIRED FOR THE CURB AND GUTTER FOUNDATION. THE BASE
MATERIAL SHALL BE COMPACTED TO 95% DENSITY (+ 3% OPTI14UM
• I. •
7. THIS CURB DOES NOT MEET HANDICAPPED ACCESS RE"BeM AND
SHALL NUT BE USED FOP ACCESS TM�4
REV:10/31/08
STAND
I
CONSTRUCT
CITY OFION KALISPELLARDS I DRIVE OVER CURB & GUTTER I SD-6
R4" S R11"
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1. 1/2" EXPANSION JOINT M M14 SHALL BE PLACED AT EACH POINT OF
CURVATURE AND POINT OF TANGENCY.
2. CONTRACTION JOINTS SHALL BE PLACED AT EVERY JT OF CURB LENGTH
AND SHALL HAVE A KKNUM DEPTH OF 3/4' AND A MINIMUM WIDTH OF
1/8'. CONTRACTION JOINTS SHALL BE CONSTRUCTED BY SAWING OR
SCORING. A TOO- SHALL BE USED WHICH WILL LEAVE CORNERS ROUNDED
AND DESTROY AGGREGATE INTERLOCK FOR THE SPECIFIED MINIMUM
DEPTH.
3. VISIBLE EDGES SHALL BE FINISHED TO A RADIUS OF 1/4, UNLESS OTHERWISE NOTED.
4. CONCRETE Stall BE M-40M WITH 3/4" MAXIMUM AGGREGATE, MINIMUM
28-DAY STRENGTH OF 4000 PSI, 696+ 11/2% AIR ENTRAINMENT, AND
MAXIMUM SLUMP OF 4".
5. INDMDUAL CONTRACTORS FORMS MAY VARY SLIGHTLY FROM THIS
PATTERN. PATTERNS DIFFERING MATERIALLY FROM THE ABOVE
DIMENSIONS SHALL BE SUBMITTED TO THE CITY FOR REVIEW.
6. FOUR INCHES OF CRUSHED GRAVEL BASE MATERIAL, -3/4' DIAMETER
IS REQUIRED FOR THE CURB FOUNDATION. THE BASE MATERIAL. SHALL
BE COMPACTED TO 95% DENSITY L 3% OPMUM MOISTURE) PER AASHTO T-99.
7. ONLY ALLOWED WITH SPECIFIC APPROVAL OF CITY ENGINEER.
REV: 10/31/08
CONSTRUCTION STANDARDS CITY OF KALISPELL STRAIGHT CURB SD-7
SIDEWALK
",LOCAL ST -
fi' COLLECTOR
S=2.00% MAX S=2.00% MIN
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I:Is1914XVIsViIII
1. PRE -FORMED 1/2" EXPANSION JOINT MATERIAL MEETING THE REQUIREMENTS
OF AASHTO M-213 SHALL BE PLACED AT 45-FOOT INTERVALS AND AT ALL
COLD JOINTS.
2. CONTRACTION JOINTS SHALL BE SPACED THE APPROXIMATE SAME
DIMENSION AS THE WIDTH, BUT NOT TO EXCEED SIX FEET.
CONTRACTION JOINTS SHALL BE CONSTRUCTED BY SAWING OR SCORING.
A TOOL SHALL BE USED WHICH WILL LEAVE THE EDGES ROUNDED AND
DESTROY AGGREGATE INTERLOCK FOR THE SPECIFIED MINIMUM DEPTH.
CONTRACTION JOINTS SHALL BE A MINIMUM OF I/4 OF THE TOTAL DEPTH
OF THE CONCRETE.
3. ALL VISIBLE EDGES AND JOINTS SHALL BE ROUNDED WITH AN EDGING TOOL WITH
A MINIMUM 114" RADIUS.
4, CONCRETE SHALL BE M-4000 WITH 3/4" MAXIMUM AGGREGATE, MINIMUM
2$-DAY STRENGTH OF 4000 PSI, 6%+ 1 1/2% AIR ENTRAINMENT, AND
MAXIMUM SLUMP OF 4".
5. SIX INCHES OF CRUSHED GRAVEL BASE MATERIAL, -3/4" DIAMETER IS REQUIRED
FOR THE SIDEWALK FOUNDATION. THE BASE MATERIAL SHALL BE COMPACTED
TO 95% DEN5ITY (+ 3% OPTIMUM MOISTURE) PER AASHTO T-99.
6. SIDEWALK THICKNESSES:
RESIDENTIAL: 4"
COMMERCIAL: 6"
REV: 10/31 /081
CONSTRUCTION
CITY OF KALISPELDARaS
SIDEWALK SD-8
157
A
'
SIDEWALK
6'R
6' IN BOULEVARD C014CRETE
FLOWLINE
GURB q4D-GMER
SD-5 OR SD 7)
7
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, 4" CONCRETE W/6" BASE MATERIAL
12%*'m (4" RESIDENTIAL- 6" COMMERCIAL)
4" BASE MATERIAL
SECTION A -A
BASE MATERIAL SHALL BE CRUSHED GRAVEL, —3/4" DIAMETER
COMPACTED TO 95% DENSITY (+ 30,4-OPTIMUM MOISTURE) PER AASHTO T-99
CONCRETE SHALL BE M-4000 WITH 3/4" MAXIMUM AGGREGATE, MINIMUM
28-DAY STRENGTH OF 4000 PSI, 6% + 1 1/2% AIR ENTRANEMENT, AND
MAXIMUM SLUMP OF 4"
REV: 10/31/08
CONSTRUCTION STANDARDS
CITY OF KALISPELL
DRIVEWAY DETAIL FOR CURB & GUTTER
SD-9
A
SIDEWALK
60 IN 6'R�y CONCRETE
BOULEVARD
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2% MA)(
DRIVEWAY SECTION
4'--J '---�BASE MATERIAL
SECTION A -A
BASE MATERIAL SHALL BE CRUSHED
GRAVEL, -3/4" DIAMETER
COMPACTED TO 95% DENSITY (+ 3% OPTIMUM MOISTURE) PER AASHTO T-99
CONCRETE SHALL BE M-4000 WITH 3/4" MAXIMUM AGGREGATE, MINIMUM
28-DAY STRENGTH OF 4000 PSI, 6%
1 1/2% AIR ENTRANEMENT, AND
MAXIMUM SLUMP OF 4"
REV: 10/31/08
CONSTRUCTION STANDARDS
CITY OF KALISPELL
DRIVEWAY DETAIL FOR STRAIGHT CURB
SD-10
14" THICKNESS OF 3 - 6 INCH STONE
MIN LENGTH * MIN WIDTH *
RESIDENTIAL 30 FEET 15 FEET
COMMERCIAUBLISINESS 60 FEET 25 FEET
Rock Construction Entrance: Conform W the Drawing and the Following'
• 3" - 6" diameter washed rock.
• Underlying Filter Fabric Requirements: See below
Woad Slash Mulch Construction Entrance:
• Raw wood slash only. No chipped -up manufactured wood or 6conicaliy treated wood is allowed.
• Splinler material to an average approximate leogtb of h inches with a maximum length of 20 inches. Bark and woad
splinters less than 2 inches long stall um exceed 20 percent by mass of tht material.
• Underlying Geotexule: See below
• Minimum Thickness of Slash Mulch Placed: 14 inches.
Construction Entrance Filler FabricGeotexdk Property Rcquiremems:Grab tensile strength minimum = 200lbs (ASTM
D4632)
• Elongation minimum = 1544 (ASTM D4632)
• Seam veaking strength miuinnun= 180 Ibs (ASTM D4632)
• Apparent opening size maximum = 0.3 mm (950 sieve) (AS1M D4751)
• Penmirtiviry minimum = 0.31see (ASTM D4491)
ALL VEHICLES ENTERING AND EXITING THE CONSTRUCTION ANOIOR BUILDING SITE SHALL TRAVERSE THE VEHICLE
TRACKING PAD TO MINIMIZE MUD AND DIRT FROM TRACKING OFFSITE. ROCK SHALL BE REPLENISHED IF TRACKING
OCCURS. TRACKING PAD SHALL BE RENEWED AS NECESSAY TO RETAIN ITS EFFECTIVENESS. ALL MATERIAL
SPILLED, DROPPED, WASHED OR TRACKED FROM VEHICLES ONTO ROADWAYS SHALL BE REMOVED IMMEDIATELY.
,> wsykliffol.]
CONSTRUCTION STANDARDS
CITY OF KALISPELL VEHICLE TRACKING CONTROL 5❑-11
100
HUB OR BELL OF EQUAL
DIAMETER AS SERVICC' '"'C
1. THIS TYPE OF CONNECTION SHALL BE USED ON
EXISTING MAINS OF 15 INCHES OR LARGER DIAMETER.
2. HUB OR BELL OF EQUAL DIAMETER AND TYPE OF
PIPE WHICH WILL BE USED FOR THE SERVICE LINE
SHALL BE USED FOR THE CONNECTION FITTING TO
THE EXISTING MAIN.
3. HUB OR BELL SHALL NOT PROTRUDE MORE THAN 1/4
INCH INTO EXISTING MAIN.
4. ALL CONNECTIONS TO MAINS SHALL BE
WATERTIGHT. A FILLET OF GROUT OR EPDXY SHALL
BE APPLIED AROUND THE DIAMETER OF THE HUB OR
BELL TO ASSURE A WATERTIGHT, LEAKPROOF
CONNECTION.
5. CONNECTION DETAILS SHALL BE SUBMITTED TO THE
PUBLIC WORKS DEPARTMENT FOR APPROVAL
PRIOR TO INSTALLATION.
6. ALL CONSTRUCTION PHASES OF THIS TYPE OF
CONNECTION SHALL BE INSPECTED BY THE
PUBLIC WORKS DEPARTMENT.
7. EXISTING LINES LESS THAN 15 INCH DIAMETER SHALL
BE TAPPED WITH AN APPROVED, COMMERCIALLY
AVAILABLE TAPPING SADDLE.
CONSTRUCTION CITYOFKA IS STANDARDS I STORMSERVICE RCONNECTIONS & SANITARY ER I SD-12 I
101
12' CONCRETE VALVE COLLAR
ALL VISHE EDGES AND JOINTS SHALL BE ROUNDED WITH
AN EDGING TOOL WITH A MINIMUM 11C RADIUS.
CONCRES SHALL BE M4W0 WITH 31C MAXIMUM
AGGREGATE, MINIMUM 28-DAY STRENGTH OF 4000 PSI, S%+
1 1/2%Alit ENTRANMENT AND MAXIMUM SLUMP OF C.
SET DEPTH OF VALVE BOX IN ACCORDANCE WITH
MPWSS STANDARD DRAWING NO.02213-2 -
.W �..A.IL1/V - I AO
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S" THICK 314 MINUS
S' THK]( CONCRETE
VALVE BOX COLLAR DETAIL
SET DEPTH OF RING IN ACCORDANCE WITH
MPWSS STANDARD DRAWING NO, 02213-1
S' THICK 304 MINUS CRUSHED STONE BASE
MANHOLE COLLAR DETAIL
ICON CITY OFIKALISON PELL RDS I MANHOLE AND VALVE BOX COLLAR I SD-13 I
102
TAPPING SADDLE:
3/4" THROUGH 2" - MUELLER BR213 SERIES BRONZE
3" & LARGER - ROMAC SSTIII STAINLESS STEEL TAPPING SLEEVE
SERVICE LINE: w
3/4" THROUGH 3" - PE Z
4" & LARGER - CLASS 150 PVC z MUELLER H-10308 CURB BOX
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MUELLER 300 SERIES CORP. STOP
MUELLER 300 SERIES CURB STOP
-' MUELLERiHUNT THERMAL -COIL
METER BOX WITH DUAL CHECK
VALVE BACKFLOW PREVENTER,
INSULATING PAD, AND CENTER
LOCKING LID.
FILTER FABRIC
SET CURB BOX AND METER
BOX AT FINISHED GRADE
METER BOX INSULATION PADS SHALL BE PROVIDED AS FOLLOWS:
3/4" METER -1S" INSULATION PAD
1" METER -18" INSULATION PAD
NOTE: METER BOXES ARE REQUIRED WHERE METERS
CANNOT BE INSTALLED IN FROST PROOF AREAS WITHIN
THE STRUCTURE.
REV:10/31/08
CONSTRUCTIONCITY OFKAL SPELLDS I WATER SERVICE LINE I SD-14
103
WATER MAINS AND SERVICES
SANITARY AND STORM SEWER MAINS AND SERVICES
REPAIR SURFACE TO ORGINAL
OR BETTER CONDITION --
4" ASPHALT IN TWO EQUAL LIFTS - DENSITY AND
SURFACE REQUIREMENTS SHALL BE IN
ACCORDANCE WITH MPWSS SEC 02510
PARAGRAPH 3.28
6- CRUSHED GRAVEL BASE,
9"-12' SELECT- SUBBASE
3" MINUS CRUSHED
SECTIONMPWSS .
PARAGRAPH c
1.5" TO 3.5 " DIAMETER CRUSHED STONE
TO STABILZE UNSTABLE FOUNDATION
AS DIRECTED BY PROJECT ENGINEER
ALL PIPE BEDDING AND TRENCH
BACKFILL SHALL BE COMPACTED TO 95
% DENSITY (± 3% OPTIMUM MOISTURE)
IN ACCORDANCE WITH AASHTO T-99
ALL TRENCH CONSTRUCTION SHALL
CONFORM TO CURRENT OSHA STANDARDS -
EXCAVATIONS
INSTALL DETECTABLE WARNING TAPE
AND TONER WIRE ON ALL WATER
MAINS AND SEWER FORCE MAINS PER
SECTION DS-02 AND DS-03
BEDDING, HAUNCHING & INITIAL
BACKFILL SHALL BE 3/4- MINUS
CRUSHED STONE, A CLEAN MEDIUM OR
COARSE SAND (UNIFIED SOIL
CLASSIFICATION AND/OR ASTM), OR
ENGINEER SHALL SUBMIT
DOCUMENTATION THAT THE BEDDING,
HAUNCHING AND INITIAL BACKFILL WILL
MEET THE REQUIREMENTS FOR CLASS
1 B MATERIALS AS DEFINED IN ASTM D
2321 WITH A MAXIMUM PARTICLE SIZE
OF 314"
REV:10/31/08
I CONSTRUCTION
SSTANDARDS I TYPICAL UTILITY TRENCH ISD-15 I
104
ALL SIGN BLANKS SHALL BE 0.080 GAUGE FLAT 18" MINIMUM BACK OF CURB
ALUMINUM STOCK. TO EDGE OF SIGN
STREET NAME SIGNN BLANKS SHALL BE 9' IN
HEIGHT. LENGTH SHALL BE DETERMINED BY
THE STREET NAME. I I i s�wm I
STOP SIGN FACES SHALL BE3M HIGH ( C I I 30" 'STOP' SIGN
INTENSITY GRADE REFLECTIVE SHEETING OR l
APPROVED EQUAL
STREET NAME SIGN BACKING SAHLL BE 3M
GREEN 3277 HIGH INTENSITY GRADE
RIGID GALVANIZED PIPE
REFLECTIVE SHEETING OR APPROVED EQUAL
X:2"
LETTERING SHALL BE 6' HIGH IN CAPITAL
0_
10' LONG 2" ID 2 3/8" OD
LETTERS'
LV
STOP SIGNS SHALL BE ATTACHED TO THE SIGN
=
POST WITH A U-BOLT STYLE SIGN MOUNTING
CLAMP.2"
GALVANIZED
STREET NAME SIGNS SHALL BE ATTACHED TO
z
COUPLING FLUSH WITH
THE TOP OF THE SIGN POST WITH A ROUND
CAP SIGN HOLDER WITH A 6' LONG MOUNTING
—
TOP OF CONCRETE BASE
BRACKET. A 6' LONG 90' CROSSPIECE SHALL
BE USED FOR DUAL SIGN APPLICATIONS.
12" DIA. X 24" DEEP 3000
PSI CONCRETE BASE
1/2" X 4" HEX BOLT ANCHOR
4' MIP
G�aTAlI�1�7/I7
CONSTRUCTION STANDARDS I STREET SIGNS I SD-16 I
CITY OF KALISPELL
16
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CONSTRUCTION STANDARDS
CITY OF KALISPELL
STREET INTERSECTION GUTTER
SD-17
100
6' R Q� 5�0� �y
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INSTALL 24" X 60' TRUNCATED DOME
PANEL IN ACCORDANCE WITH THE ADA
ACT.
1. PEDESTRIAN RAMPS SHALL COMPLY WITH THE AMERICANS WITH
DISABILITIES ACT/ACCESSIBILITY GUIDELINES FOR BUILDINGS AND FACILITIES.
2. THE LEAST POSSIBLE SLOPE SHALL BE USED FOR PEDESTRIAN RAMPS. THE
MAXIMUM SLOPE SHALL BE 1:12 (8.33%).
3. THE CROSS SLOPE SHALL BE NO GREATER THAN 1:50 (2.00%).
4. A LANDING AREA THE WIDTH OF THE RAMP AND AT LEAST 36 INCHES IN
LENGTH SHALL BE PROVIDED AT THE TOP OF THE RAMP. SLOPE OF THE
LANDING SHALL NOT EXCEED 1:50 (2.00%) IN ALL DIRECTIONS.
5. ALTERNATE DESIGNS AND LOCATIONS SHALL MEET THE REQUIREMENTS OF
THE AMERICANS WITH DISABILITES ACT/ACCESSIBILITY GUIDELINES FOR
BUILDINGS AND FACILITIES AND SHALL BE APPROVED BY THE PUBLIC WORKS
DEPARTMENT PRIOR TO START OF CONSTRUCTION.
6. PEDESTRIAN RAMPS SHALL BE A MINIMUM OF 60 INCHES WIDE. REV:10131=
I CONSTRUCTION
CTION STANOF S E DARDS ( PEDESTRIAN RAMP SD-18
CIT
107
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TRUNCATED DOME
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IMRM
00
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MAXIMUM 1:12
RETROFIT ARE
a d o o f l
MAXIMUM
1. PEDESTRIAN RAMPS SHALL COMPLY WITH THE AMERICANS WITH DISABILITIES
ACTIACCESSIBILITY GUIDELINES FOR BUILDINGS AND FACILITIES.
2. IN INSTANCES WHEN IT WILL BE TECHNICALLY INFEASIBLE FOR A PEDESTRIAN RAMP TO BE
CONSTRUCTED TO FULL AND STRICT COMPLIANCE WITH ADA STANDARDS, THE
PEDESTRIAN RAMP MUST BE INSTALLED TO PROVIDE ACCESSIBILITY TO THE MAXIMUM
EXTENT FEASIBLE. ALTERNATIVE DESIGNS SHALL BE APPROVED BY THE PUBLIC WORKS
DEPARTMENT PRIOR TO CONSTRUCTION.
CONSTRUCTION STANDARDS '
CITY OF KALISPELL RETROFIT PEDESTRIAN RAMP SD-19
168
PAVEMENT GRADE
❑ESIGN TOP OF CURB GRADE
0.2 FT BELOW ❑ESIGN
TOP OF CURB GRADE
2'
0.2 FT BELOW
PAVEMENT GRADE
0.2 FT BELOW DESIGN
TOP OF CURB GRADE
(SET TO LONGITUDINAL
STREET GRADE)
1. REINFORCE CONCRETE WITH 10110 6 X 6
WWF SUPPORTED WITH #3 REINFORCING
BARS AT 48" ON CENTER EACH WAY ON 3"
HIGH CHAIRS
2. CONSTRUCT PR10R TO PAVING.
10131 /08
CONSTRUCTION STANDARDS CONCRETE CURB INLET APRON I SD-20
CITY OF KALISPELL
169
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