HomeMy WebLinkAboutDrainage Reports - 01/05/1989FINAL DRAINAGE REPORT
SEVEN LAKES P.U.D. PHASE II SUBDIVISION
STEWART & ASSOCIATES, INC.
January 5, 1989
STEWART&ASSOCIATES
Consulting Engineers and Surveyors
January 5, 1989
Mr. Robert Smith
Storm Drainage Utility
City of Fort Collins
P 0 Box 580
Fort Collins, Co. 80522
Dear Bob:
This is the final storm drainage report for Seven Lakes P.U.D., Phase
II Subdivision, which is situate in the Southwest '' of Section 17,
Township 7 North, Range 68 West of the Sixth P.M. It is located on the
North side of East Prospect Road between Prospect Park Way and Sharp
Point Drive. It contains 11.24 acres net and is zoned I.P. — Planned
Industrial. The site is in the Spring Creek Basin and is near the
confluence of Spring Creek and the Cache la Poudre River.
The site is in the Spring Creek flood plain according to the Flood
Insurance Rate Map, Panel No. 080102 0004 A dated July 16, 1979. Since
the map was published, Spring Creek has been relocated to the North and
flows through several existing ponds. The flood plain map has not been
revised, however we are proposing the floor elevations be elevated to
at least 1.50 feet above the 100 year flood elevation shown on the FIRM
map.
Because of the very close proximity to both Spring Creek and the Cache
la Poudre River there will be no onsite storm water detention provided.
Approximately 8.5 acres of the developed portion of Seven Lakes P.U.D.
drains onto this site from the West. The North half of East Prospect
Road drains Easterly in the existing and proposed curb and gutter to
Sharp Point Drive and then Northerly to the existing drain swale at the
North property line. The existing and proposed development drain
Northerly and Easterly internally and away from East Prospect Road.
The runoff from East Prospect Road and Sharp Point drive in a ten year
storm is 6.63 cubic feet per second and can be carried in the curb and
gutter. The land lying Easterly and .Northerly of this site drains to
Spring Creek and the Cache la Poudre River and not onto this P.U.D.
The developed portion of Seven Lakes drains to this site in an existing
concrete pan and through the site in an existing temporary drainage swale
that will be relocated. The off site storm water from the West, when
fully developed, will be 15.17 cubic feet per second in a two year storm.
A double area inlet will collect part of this two year storm water and
the low flow water and discharge into an 18 inch storm drain that will
James H. Stewart —2—
and Associates, Inc.
214 N. Howes Street
P.O. Box 429
Ft. Collins, C080522
303/482-9331
Mr. Robert Smith
January 5, 1989
Page 2
carry it to the relocated drainage swale. The concrete pan will continue
Easterly and Northerly to carry the overflow water to the drainage swale.
This storm drain and pan will be built with the Phase I building,
A 15 inch storm drain is proposed for Sub —basin II because of the flat
grades encountered. Most of the site is being filled so minimum grades
were designed to minimize the amount of fill material required. The
Westerly two inlets and the pipe discharging them will be built in Phase
I and the rest of the pipe system will discharge into a temporary drain
swale that will carry the storm water to the Northeast corner of the
P.U.D.
The main drainage swale along the North property line will be completed
in Phase I. The Easterly 400 feet of the Swale is existing and it and
the new reach of the swale will carry the 100 year fully developed flow
of 103.7 cubic feet per second.
The storm water run off calculations using the Rational Method and the
calculations for sizing of the swales are enclosed. Also a reduction
of the grading and drainage plan is enclosed.
If you have any questions regarding this report, please call.
Sincerly,
Richard A. Rutherford, P. E. & L.S.
President
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Enclosures
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