HomeMy WebLinkAboutDrainage Reports - 05/16/2012February 8, 2012
Mr. Wes Lamarque
City of Fort Collins
Storm Water Utility
700 Wood Street
Fort Collins, CO 80522
INTERWESTim, �7
I CONSULTING G R O U P
City of Ft. Collins rov Plans
Approved By
Date
LT
Re: Radiant Park— Lot 1 of Staley/Poudre School MLD 00-S1535
Storm Drainage Report
Dear Wes,
Please accept the following letter on behalf of the City of Fort Collins Parks Department to
demonstrate the site's compliance with the City of Fort Collins Drainage Standards. Note that
the Erosion Control and Stormwater Management Plan report has been submitted as a separate
document.
INTRODUCTION
Radiant Park is a proposed neighborhood park located in the Northeast Quarter of Section 9,
Township 6 North, Range 68 West of the Sixth Principal Meridian, City of Fort Collins, County
of Larimer, State of Colorado. It contains 9.2 acres and is bounded on the north by Kechter
Road, the south by Muskrat Creek Drive, the west by Outlot I of Fossil Lake P.U.D., Second
Filing and the east by Zach Elementary School. The site is bisected by McClellands Creek.
Please refer to the attached vicinity map.
The site is in the McClellands Basin and is included in the City's Storm Water Management
Model (SWMM) basins 503 and 504.
EXISTING CONDITIONS
The site currently has an existing concrete trail system and pedestrian bridge but otherwise is
vacant. The north portion of the site sheet flows south to McClellands Creek and the south
portion of the site sheet flows north to McClellands Creek.
1218 WEST ASH, SUITE C WINDSOR, COLORADO 80550
TEL. 970.674.3300 • FAX. 970.674.3303
Mr. Wes Lamarque
February 8, 2012
Page 2 of 3
PROPOSED DEVELOPMENT
The proposed development consists of a new concrete trail system, sand play ground area,
restroom and shelter and educational platforms with seating areas. The site will also include a
play field and a new pedestrian bridge. The existing pedestrian bridge is to be removed, with a
new bridge spanning the Erosion Buffer installed to the southeast of the site.
The bottom chord of the new core area bridge is to be set at a minimum elevation of 4886.08 in
order to free span the proposed 100-year WSEL of McClellands Creek. The existing and
proposed floodplain documentation is in a separate report "Floodplain Modeling Report for
Radiant Park". The shorter bridge located to the southeast of the site is breakaway.
BASIN DESCRIPTIONS
The site is divided into two basins, the northern (Basin A) and the southern (Basin B). The
basins are delineated on the Erosion Control plan which is attached to this report.
Basin A is comprised of the portion of the site north of McClellands Creek. It includes a concrete
trail system, play equipment, shelter and the drive aisle of Zach Elementary. This basin drains to
the south to McClellands Creek. The time of concentration for this basin is 13.6 minutes.
Basin B is comprised of the portion of the site south of McClellands Creek. It includes a concrete
trail system, playground, restrooms and the educational platforms. This basin drains to the north
to McClellands Creek. The time of concentration for this basin is 14.2 minutes.
According to the SWMM model, the peak flow of McClellands Creek in this area is at a time of
1 hour and 20 minutes. Please refer to the appendix for reference to the model. Because our
basins' time of concentrations are much shorter than the time to peak flow of McClellands
Creek, it has been deemed acceptable by the City that detention will not be provided for this site.
WATER QUALITY
As the drainage leaves the site, water quality will be achieved through a network of best
management practices (BMPs) including grass buffers, a grass swale and permeable pavement
systems.
The grass buffer between the concrete trail and McClellands Creek will treat most of the
concrete trail area. Water will sheet from the concrete trail to the grass buffer where filtration of
sediment will occur before the water reaches McClellands Creek.
A grass swale, located in basin B will treat a portion of the sidewalk located on the west portion
of the site. The swale will convey flow in a slow and shallow manner were filtration of sediment
will occur. Flow will be directed to a culvert where it will then flow north to McClellands
Creek. A scour stop system will be used as a level spreader at the outlet of this pipe.
Mr. Wes Lamarque
February 8, 2012
Page 3 of 3
The playground area will have a surface area of sand which will also facilitate sedimentation.
An underground drain system will drain to a large culvert located in the educational platform
area. This culvert directs flow to McClellands Creek
The educational platform areas are all pervious pavement systems which will allow movement of
water into the layers below the pavement surface thus providing treatment and reduce effective
imperviousness.
The building and shelter includes approximately 2,500 sf of impervious area. Bioretention was
considered as a treatment option for this area; however, it has been determined that the specified
planting for this site will not work with the required media or shape of the bioretention facility.
Water instead will go through a dense shrub bed and then about 40 to 50 feet of native planting
prior to entering the low flow channel state of McClellands Creek.
CONCLUSION
The design minimizes impacts to other utilities and properties and maintains the existing
drainage flow paths as much as possible. The design will effectively control damage from storm
runoff originating from the site. The recommended BMPs are sufficient to reduce runoff peaks,
volumes and pollutant loads from the relatively minimal impervious areas of the site.
We appreciate your time and consideration in reviewing this submittal. Please call if you have
any questions (970) 674-3300 Ext. 103.
Sincere ,
r1D
Erika Schneider, P.E. Colorado Professional Engineer 41777
Interwest Consulting Group
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ENVIRONMENTAL PROTECTION AGENCY - STORM WATER MANAGEMENT MODEL - VERSION PC.1
DEVELOPED BY METCALF + EDDY, INC.
UNIVERSITY OF FLORIDA
WATER RESOURCES ENGINEEERS, INC. (SEPTEMBER 1970)
UPDATED BY UNIVERSITY OF FLORIDA (JUNE 2973)
HYDROLOGIC ENGINEERING CENTER, CORPS OF ENGINEERS
MISSOURI RIVER DIVISION, CORPS OF ENGINEERS (SEPTEMBER 1974)
BOYLE ENGINEERING CORPORATION (MARCH 1985, JULY 1985)
TAPE OR DISK ASSIGNMENTS
JIN(1) JIN(2) JIN(3) JIN(4) JIN(5) JIN(6) JIN(7) JIN(8) JIN(9) JIN(10)
2 1 0 0 0 0 0 0 0 0
JOUT(1) JOUT(2) JOUT(3) JOUT(4) JOUT(5) JOUT(6) JOUT(7) JOUT(6) 17OUT(9) JOUT(10)
1 2 0 0 0 0 0 0 0 0
NSCRAT(1) NSCRAT(2) NSCRAT(3) NSCRAT(4) NSCRAT(5)
3 4 0 0 0
WATERSHED PROGRAM CALLED
*** ENTRY MADE TO RUNOFF MODEL •••
MCCLELLANDS BASIN MODEL (FULLY INTEGRATED) EXISTING CONDITIONS JUN 30 1999
ADOPTED 100-YEAR EVENT FILE: MMCEX.DAT Used for EXTRAN hydrographs 3/22/00
NUMBER OF TIME STEPS 600
INTEGRATION TIME INTERVAL (MINUTES) 1.00
1.0 PERCENT OF IMPERVIOUS AREA HAS ZERO DETENTION DEPTH
FOR 25 RAINFALL STEPS, THE TIME INTERVAL IS 5.00 MINUTES
FOR RAINGAGE NUMBER 1 RAINFALL HISTORY IN INCHES PER HOUR
1.00 1.14 1.33 2.23 2.84 5.49 9.95 4.12 2.4B 1.46
1.22 1.06 1.00 .95 .91 .87 .84 .81 .78 .75
.73 .71 .69 .67 .00
MCCLELLANDS BASIN MODEL (FULLY INTEGRATED) EXISTING CONDITIONS JUN 30 1999
ADOPTED 100-YEAR EVENT FILE: MMCEX.DAT Used for EXTRAN hydrographs 3/22/00
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Interwest Consulting Group
RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: Radiant Park
PROJECT NO: 1096-012-56
COMPUTATIONS BY: es
DATE: 21612012
Recommended Runoff Coefficients from Table 3-3 of City of Fort Collins Design Criteria
Recommended % Impervious from Urban Storm Drainage Criteria Manual
Streets, parking lots (asphalt):
Sidewalks (concrete):
Roofs:
Landscape Areas:
Runoff
%
coefficient
Impervious
C
0.95
100
0.95
96
0.95
90
0.25 1
0
SUBBASIN
DESIGNATION
TOTAL
AREA
(ac.)
TOTAL
AREA
(sq.ft)
ROOF
AREA
(sq.ft)
PAVED
AREA
(sq.ft)
SIDEWALK
AREA
(sq.ft)
LANDSCAPE
AREA
(sq.ft)
RUNOFF
COEFF.
(C)
%
Impervious
A
3.3
142,662
0
11,271
12,426
118,965
0.37
16
B
5.9
255,834
600
0
17,808
237,426
0.30 1
7
Total
9.15 1
398,495 1
600 1111.271
30,234 1
356.391 1
0.32
10
Equations
- Calculated C coefficients & % Impervious are area weighted
C=s(Ci Ai) /At
Ci = runoff coefficient for specific area, Ai
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
At = total area over which C is applicable; the sum of all Ai's
Cval and Imperviousness.xls
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