HomeMy WebLinkAboutREINHOLTZ / FORNEY PUD - PRELIMINARY & FINAL - 61-87 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTFINAL DRAINAGE REPORT
FOR
CHAPARRAL P.U.D.
FORT COLLINS, COLORADO
PREPARED FOR:
PROGRESSIVE LIVING STRUCTURES
PREPARED BY:
SHEAR ENGINEERING CORPORATION
DECEMBER, 1987
PROJECT NO: 1005-5-86
4431 Hollyhock, Ft. Collins, CO 80526 (303) 226-5334
GENERAL LOCATION AND DESCRIPTION
Chaparral P.U.D. is a 10.04 acre tract. located in the. Southeast
Quarter of Section 27, T 7 N, R 69 W of the 6th P.M., in the City
of Fort Collins, Colorado.
More specifically, Chaparral P.U.D. is located at the Southwest corner
of the intersection of Shields Street and Casa Grande Boulevard. It
is the last portion of the original Wagon Wheel subdivision to be developed.
This property was originally a part of the 3rd Filing of Wagon Wheel
Subdivision. Wagon Wheel Subdivision, 3rd Filing was replatted as Casa
Grande P.U.D. Chaparral P.U.D. is now a replat of Tracts 3 and 4
of Casa Grande P.U.D.
Please refer to the grading/drainage plan attached for actual Chaparral
boundaries.
Chaparral P.U.D. will consist of 55 single family lots.
DRAINAGE BASINS AND SUB -BASINS
Chaparral P.U.D. is contained within, and is a part of the Wagon
Wheel Subdivision Master Drainage Plan. Wagon Wheel Subdivision
and Chaparral P.U.D. is contained within, and is a part of, the City
of Fort. Collins Spring Creek Basin.
® A detention pond will be provided on the Chaparral P.U.D. site to
satisfy the detention requirements for approximately 31 acres of up-
stream development which includes Wagon Wheel Subdivision Filing 2,
Casa Grande P.U.D. and Chaparral P.U.D. The pond location is con-
sistent with the proposed pond location in the Wagon Wheel Subdivision
Master Drainage Plan.
An 18" RCP storm sewer, which is located in Lymen Street, directly
north of Chaparral P.U.D., and which directs storm flows to a larger
detention facility in the. Northeast corner of Wagon Wheel Subdivision,
dictates the Chaparral P.U.D. detention pond release rate and in turn,
the size of the detention pond for the contributing area to the pond.
The existing 18" RCP storm sewer and end section currently located
on the Chaparral P.U.D. site, will be utilized as the pond outlet.
(See grading and drainage plan.)
There is a 24" RCP storm sewer in Casa Grande Boulevard which
directs storm flows to the same inlet which accepts storm flows from
the existing 18" RCP on the Chaparral P.U.D. site. All flows which
enter this inlet, release into the previously discussed 18" RCP storm
sewer in Lymen Street.
It is evident that during less frequent rainfall events, as the 18"
RCP in Lymen Street reaches its capacity, the 24" RCP will begin
to back up at the same rate as the detention pond. The 24" RCP
is therefore considered to contribute to the detention pond.
0
DRAINAGE DESIGN CRITERIA
The rational method for determining peak flows to various design points
was used for establishing inlet sizes, storm sewer flows and required
sizes and street flows. Rational method analysis begins upstream of
Chaparral P.U.D., utilizing existing drainage reports for Wagon Wheel
Subdivision. The cumulative runoff method for determining detention
requirements was used. The maximum capacity of the existing 18"
RCP storm sewer in Lymen Street is 6.6 cfs. This will be used as
the detention pond release rate. Figures from the Storm Drainage
Design Criteria used with this report are included for reference.
DRAINAGE FACILITY DESIGN
All storm drainage facilities which are not currently constructed, have
been designed according to City of Fort Collins Storm Drainage Design
Criteria. Figures from the Storm Drainage Criteria used with this
report are included for reference. Figure 5-1 for storm sewer design
data summarizes storm sewer design.
CONCLUSIONS
A storm 'sewer system for the remaining contributing area to the deten-
tion pond area is provided. The detention pond will detain storm
flows for 2 year storms as well as less frequent storms, .because the
18" storm sewer in Lymen Street has a capacity of 6.6 cfs which is
® less than 2 year design flows to Concentration Point 5 (detention pond
outlet) . This includes those flows in Casa Grande Boulevard and
the existing 24" RCP in Casa Grande Boulevard, installed with the.
development of Wagon Wheel Subdivision.
The available storage in the detention pond is approximately 3.5 acre
feet. An overflow will be provided along the Shields Street berm,
with an elevation of 78.50. Storm flows from smaller frequency storms,
once the detention pond capacity has been reached, will spill over
into Shields Street and Foothills Drainage Basin. These flows enter
the Cunningham Corners drainage system. and continue within the Foothills
Basin drainage system.
The Chaparral storm sewer system has been designed so that no, sur-
charging occurs within the system once the detention pond capacity
is reached. Refer to storm sewer construction drawings for additional
information.
REFERENCES
® 1. Final Drainage Study, Wagon Wheel Subdivision; Melody Construction
Company; Revision date: October, 1979.
2. Revision to Final Drainage Study, Wagon Wheel Subdivision, Third
Filing; Melody Construction Company; Dated: April 3, 1981.
3. Final Drainage Report for Casa Grande P.U.D. ; Shear Engineering
Corporation; Revision date: July, 1985.
4. Drainage Study for Horsetooth Commons P.U.D. ; Red Peak En-
gineering; Dated: January, 1987.
5. City of Fort Collins Storm Drainage Design Criteria; May, 1984.
11
11
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DRAINAGE CRITERIA MANUAL
STORM SEWERS
DesignLocation
of
angni-M-Laugnnn cnymtsn
FIGURE 6-1. TYPICAL FORM FOR STORM DRAINAGESYSTEM PRELIMINARY DESIGN' DATA
rFtcC�CC-T
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FIGURE 6 •
STORM DRAINAGE CRITERIA MANUAL
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REFERENCE: 'Urban Hydrology.For Small Watersheds" Technical
Release No. 55. USDA, SCS Jan. 1975.
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