HomeMy WebLinkAboutSPRING CREEK FARMS REZONING - 24-00C - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE RELATED DOCUMENTsubsequently, through a proposed storm sewer network to the proposed storm water detention
and water quality facility (refer to the attached Master Drainage Plan sheet 1 of 2)
Pursuant to a conversation with Mr. Wes Lamarque, City of Fort Collins Utilities, the allowable
post development 100-year release rate for the drainage within the Foothills Basin is twenty
cubic feet per second (cfs) or . 0.4 cfs per acre. Therefore, the allowable 100-year post
development release rate for the project site is limited to 2 cfs. The detention volume estimate
was performed by routing the post -developed condition, site -specific 1-hour hydrograph with a
maximum release rate of 2 cfs. On -site soils were determined to be the "C" hydrologic group
classification according to the Soil Conservation Service's Larimer County study. Estimating a
ninety-five percent imperviousness for the site, the resulting 100-year manning's "C" coefficient
was found to be 0.89 (from Table RO-5, UDFCD Vol. I). The results of the routing reveal that
the site will require approximately 43,528 cubic feet, or 1.00 acre-foot, of detention storage.
Water quality considerations will require approximately 7,135 cubic feet, or 0.164 acre-feet,
additional storage resulting in a combined total approximate "required storage volume of 50,663
cubic feet or 1.163 acre-feet. The detention and water quality pond is proposed to be located at
the southeasterly corner of the site adjacent to the existing storm sewer outfall and,
correspondingly, at the low point of the site. The existing grate inlet was found to be
approximately seven feet in depth thereby limiting the proposed pond to approximately six feet
maximum storage depth. With an anticipated average depth of approximately three feet,
approximately one-third of an acre will be designated for the detention and water quality pond.
The Spring Creek Farms Retail project, comprising approximately 5 acres of neighborhood
commercial use, will result in planned drainage improvements within the Foothills Basin. Storm
sewer improvements and a storm water detention and water quality facility will be implemented.
This improvements will be designed to control on -site and off -site storm water runoff and
provide significant reductions in post -developed storm water runoff as well as providing for the
enhancement of post developed storm water quality.
Please feel free to contact our office at (970) 484-1921 should you have questions or desire
clarification regarding the recommendations presented in this letter report.
Sincerely,
JIM SELL DESIGN, INC. D`0�RE�`e
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cc: 2460.1 project file
2460.1 Drainage Letter 12 28 05.doa
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December 30, 2005
Mr. Glen D. Schlueter
Stormwater Development Manager
City of Fort Collins Utilities
700 Wood Street Street
Fort Collins, CO, 80522-0580
RE: Spring Creek Farms Retail
Rezoning Application
Site Improvement Proposal -Drainage Evaluation
Dear Mr. Schlueter:
LANDSCAPE ARCHITECTURE
PLANNING
ENGINEERING
GRAPHIC DESIGN
This letter report is to address the proposed concept level drainage design with regards to above
referenced project. The proposed Spring Creek Farms Retail project is a planned neighborhood
commercial use situated on a 4.98-acre tract of land located at the northwest comer of the
intersection of E. Drake Road and Timberline road within the City of Fort Collins. The project is
located within the Foothills Basin as designated by the City of Fort Collin's Stormwater
Management Master Plan. The site historically outfalls to the east along E. Drake Road. An
existing thirty-six inch storm sewer located in E. Drake Road currently serves the project site.
The project site, as well as the entire Foothills Basin, outfalls to the 100-year floodplain of the
Poudre River (refer to the attached City of Fort Collins Stormwater Drainage Basins Exhibit).
The proposed project is located within the Spring Creek Farms North parcel comprising 55.35
acres. A major basin divide, dividing the Foothills Basin on the south and the Spring Creek
Basin on the north, runs east -west through the northerly most portion of this parcel resulting in
approximately fifty -acres within the Foothills Basin drainage. The project site lies at the low
point of this approximate fifty -acre drainage, namely, the southeasterly area. Subsequently, the
remaining forty-five acres of the drainage will impact the project site. Peak runoff for the 2-, 10-
and 100-year storm frequencies were evaluated for the undeveloped condition for the off -site
areas west and north of the project site, designated sub -basin H-1 and sub -basin H-2, respectively
(refer to the attached Master Drainage Plan sheet 2 of 2). The results of that evaluation are
summarized in the following table.
Basin
Area
Final
C
C
C
2yr
10yr
100yr
Q
Q
Q
Name
Tc
2-year
10-year
100-year
Intensity
Intensity
Intensity
2-year
10-year
100-year
acres
min
in/hr
in/hr
in/hr)
(cfs)
(cfs
cfs
H-1
22.20
20.5
0.02
0.17
0.36
1.59
2.78
5.53
0.71
10.49
44.20
H-2
18.20
121.9
0.02
0.1.7
0.36
1.53
2.62
5.33
0.56
8.11
34.92
Storm water runoff from the off -site areas is proposed to be intercepted by storm sewer and
conveyed through the site. Stone water runoff within the site will be conveyed overland and,
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