HomeMy WebLinkAboutDrainage Reports - 10/24/1990DRAINAGE REPORT
FOR
THE BRIDGES II P.U.D.
PREPARED BY
STEWART & ASSOCIATES. INC.
OCTOBER 18, 1990
SITE LOCATION:
The Bridges II P.U.D. is a Replat of Part of Lot 1 of the Bridges P.U.D.,
First Filing, situate in the Northwest ', of Section 22, Township 7 North,
Range 69 West of the Sixth P.M., Fort.Collins, Larimer County, Colorado.
All construction in the Bridges P.U.D•, First Filing, lying above the
New Mercer Canal has been completed including the required detention
pond below the ditch. The purpose of the Bridges II P.U.D. is to create
two building sites in place of three building sites as shown on the
First Filing.
SITE DESCRIPTION:
The site consists of native grasses, gravel, and dirt. The slope of
the existing ground is North to South and the grades vary from 10% away
from the New Mercer Canal to 0.40% over the Southerly part of this
project. There is to be no construction below the Larimer County Canal
No. 2 or above the New Mercer Canal except for the 24 foot wide access
road. There is no offsite drainage onto the property.
PROPOSED DESIGN:
The original drainage report was designed for a developed site of 8.5
acres and an undeveloped site of 4.3 acres of .the total site area of
12.8 acres. Our development of these two buildings is a reduction of
the original design by one building. The detention required for the
site was 60,480 cubic feet. A copy of the original report is included
with this, report.
The runoff from the West building drains to the inlet in the cul—de—sac.
The runoff from the East building drains to a corner of the parking
area and then in a concrete pan to an inlet at the angle point between
the 15 inch P.V.C. and the flume across the Larimer County No. 2 Canal.
These two flow systems keep runoff from entering directly into the No.
2 Canal.
Both buildings have 4 inch perforated sub —drains designed to encompass
each building. The sub —drain discharges a maximum of 0.35 c.f.s. into
the upstream inlet. The flume will carry 8.0 c.f.s. across the No.
2 Canal. The runoff from the site in a 100 year frequency storm is
7.9 c.f.s. The detention pond has a 1.0 foot freeboard and has a 15
inch outlet pipe. The 0.35 c.f.s. of sub —drain water can be accommodated
through the pond.
Calculations have been made and are included with this report for the
sizing of the drain Swale, pipe, and area inlets.
Franklin D. Blake, P.E. & L.S. ';° J t61
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COMPUTATIONS:,'
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James H. Stewart and Associates, Inc.
Consulting Engineers and Surveyors
214 North Howes Street
P.O. Box 429
Fort Collins, Colorado 80522
(303)482-9331
March 28, 1986
Mr. Tom Gathmann
Storm Drainage Department
City of Fort Collins
P.O. Box 580
Fort Collins, Colorado 80522
Dear Tom:
Laboratory:
301 Lincoln Court
P.O. Box 429
Fort Collins, Colorado 80522
(303)484-6309
This is regarding the revised storm drainage report for the Replat of
Part of Tracts 1 and 2, The Bridges P.U.D. First Filing.
The basic changes in the plan are that an additional building is being
proposed below the New Mercer Canal and a vehicular bridge is being built
to access the buildings below the Canal. The twenty foot wide driveway
that was originally proposed between the New Mercer Canal and the Larimer
County Canal No. 2 will not be needed for emergency access. Therefore
the runoff should be reduced by a small amount because the impervious
surfacing is being reduced by a small amount.
We are, therefore, not proposing any changes in the storm drainage system
for the development. The detention pond and the underground storm drain
system have been completed. Not all of the concrete pan has been con-
structed at this time.
If you have any questions regarding this matter, please call.
Sincerely,
JAMES H. STEWART AND ASSOCIATES, INC.
Richard A. Rutherford, P.E. & L.S.
President
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