HomeMy WebLinkAboutFOOTHILLS PARKWAY PUD - PRELIMINARY - 36-89 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT (2)FINAL DRAINAGE REPORT
FOR
FOOTHILLS PARKWAY P.U.D.
NOVEMBER 1989
STEWART & ASSOCIATES, INC.
SITE LOCATION:
Foothills Parkway P.U.D. is Lot 2, a part of Lot 1, and a portion of
the vacated South College Avenue Frontage Road in the Mourning Subdivision
Fort Collins, Colorado. It is bounded on the South by Foothills Drive,
on the West by Steeles Market, on the North by Dellenbach Chevrolet,
and on the East by South College Avenue. The net area is 0.99 acres.
The gross area, not including South College Avenue is 1.14 acres more
or less.
EXISTING CONDITIONS:
The existing site is gravel covered except for the existing frontage
road and Foothills Drive which are asphalt. There is no offsite runoff
across the site. The historic flow quantity is Q2 = 1.49 c.f.s., Q10
2.63 c.f.s. and Q100 = 5.64 c.f.s.
There is an existing old City standard curb inlet on the West side of
the frontage road at the Northeast corner of the site. The inlet ties
into the Cities 48 inch storm drain at this point. Approximatly 14.7
acres of runoff from developed property goes to this curb inlet. 3.5
acres of this land is detained and the remaining 11.2 acres flows there
undetained. Figure 1 shows this area. The historic runoff to this curb
inlet is Q = 12 c.f.s., Q10 = 21 c.f.s., and Q100 = 58 c.f.s. The
capacity o� this curb inlet is 15.46 c.f.s. The overflow for this low
area is the curb on College Avenue at an elevation of 5025.4 feet plus
or minus, if the curb inlet plugs. This area now acts as a detention
pond with the high water line at elevation 5023.3 more or less. the
existing detention area is shown on Figure 1. this area is not a designed
detention area.
PROPOSED DESIGN:
It is our proposal to detain the 100 year site flow in two detention
ponds and to release at a two year historic rate. The combined historic
two year rate from the detention areas is 1.49 c.f.s. The required
combined detention is 6274 c.f.s. Our combined detention will be 8030
c.f.s. the over detention is because of the elevation of the finished
floors of the buildings. The existing runoff from Foothislls Drive will
not be routed through the ponds but will flow directly the new proposed
curb inlet. Also, the newest entrance from Foothills Drive will also
go directly to the new inlet. We are going to increase the capacity
of the new curb inlet to 18.88 c.f.s. to help the existing flooding at
the old curb inlet.
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