HomeMy WebLinkAboutFOSSIL CREEK OFFICE PARK EAST PUD PRELIMINARY AND FINAL - 52 91B - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTa . 1
James H. Stewart and Associates, Inc.
Consulting Engineers and Surveyors
September 18, 1980
Mr. Russ Legg
Subdivision Administrator
Iarimer County Planning Office
P.O. Box 1190
Fort Collins,. CO 80522
Dear Russ:
This is to explain and add information regarding storm drainage at Cameron
Park, Second Filing.
The effects of upstream development have been considered. There are approxi-
mately 193 acres in the drainage basin above the Colorado and Southern Rail-
road. This basin only extends Westerly to South Shields Street and lies
between two major basins, Mail Creek and Fossil Creeek. The basin is shown
on the enclosed U.S.G.S. map as the cross bitched area. The historic runoff
from a two year frequency storm is 27 c.f.s. and the historic runoff from a..
100 year frequency storm is 101 c.f.s.. It is our assumption that any furthe3
development West of the tracks will be required to have storm water deten-
tion and will release at a historic two year rate. Therefore, the present
conditions, with a 100 year frequency storm, could be expected, which has a
quantity of the 101 c.f.s. mentioned above. The existing 36 inch diameter
steel pipe will carry 80 c.f.s. at the present 2% slope, however, it will
carry approximately 260 c.f.s. when water is backed up to the top of the
existing railroad enbanlanent. I, therefore, have come to the conclusion
that the present pipe should not be enlarged, since the existing pipe will
carry 2 1/2 times the 100 year frequency storm.
.Uiere_are_two_additiona.l_culverts_througti the railroad embanlanent. There is
a 24" concrete culvert that is an abandoned irrigation culvert and is on top
of the hill. There also is an. existing 21" concrete culvert at the South-
west corner of Cameron Park. It drains a very small area of approximately
7 acres on the West side of the railroad. As Mr. Gregory stated at the
Planning Commission meeting, his group owns the property to the South of
Cameron Park and they will develop a small drain Swale in the existing
thalweg which is South Of the South line of Cameron Park.. Any drainage
from pots 20, 21, and 22 will be carried by the gutter, in what was known as
Sundown Road, to the drain swale in the adjacent property.
There is approximately 6 acres in the First and Second Filings which do
not drain to the ponds. This area produces a developed runoff for a two
year storm of 8.6 c.f.s. and a 100 year storm of 31.2 c.f.s.. The drainage
will be carried in Cameron Drive and the Frontage Road and across Mr.
Gregory's land to Fossil Creek. This front 6 acres will not.have detention,
however, the ponds are going to detain a greater than required quantity so
OFFICE-214 NORTH HOWES • P.O. BOX 420 0 FORT COLLINS. COLORADO 605?2 . TELEPHONE 303/482.9331
Mr. Russ Legg
September 18, 1980
Page 2
the net effect is good.
The three ponds have a surface area of approximately 52,000 square feet.
We will have at. least 2.5 feet of storm water storage above the permanent
pond water levels. New dikes, spillways, outlet pipes and drop structures
will be constructed for the middle and North ponds. The existing dikes will
be reconstructed to provide adequate protection so.that.-they will not .fail.
The enclosed drainage plan shows the preliminary plan of the proposed drain-
age system.. If you have any further questions regarding the system, please
call.
Sincerely,
JMES H. SMVART & ASSOCIATES, INC.
Richard A. Rutherford, P.E. & L.S.
Secretary -Treasurer
RAR/cj f
Enclosure
xc: Jon Gregory
o�
COMPUTATIONS
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Fort Collins, Colorado
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