HomeMy WebLinkAboutDrainage Reports - 01/13/1994Northern Engineering Services, Inc.
December 6, 1993
Mr. Glen Schleuter
Stormwater Utility
City of Fort Collins
235 Mathews
P.O. Box 580
Fort Collins, Colorado
80522-0580
re: Spring Court Storage
Amended P.U.D.
Fort Collins, Colorado
Project No. 9323.00
Dear Glen:
s C6
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Northern Engineering is pleased to submit this revised
Drainage Letter for your review. It represents a study of the
drainage characteristics for the proposed construction of two
storage buildings on the property located at 201 West Stuart
Street, Fort Collins, Colorado. Pavement surrounds the existing
buildings, therefore, the addition of new buildings will not change
the runoff characteristics of the site. Grading changes are to
accommodate the existing drainage patterns on the site. Presently,
two area inlets collect all runoff from the sub -basin. The basin's
imperviousness shall not change due to the proposed construction.
Overland flows will be channelled to the inlet at D.P.1; the
section of storm sewer up stream of that is to be abandoned. It
is assumed that the existing storm sewer is adequate in carrying
the historic runoff. The inlet capacity at D.P.1 will. be increased
by enlarging its area. The top of the grate will be raised 0.5
feet to accommodate the new grading (see Drainage Plan).
The Rational Method is used to quantify the peak flow. Storm
drainage criteria for the city of Fort Collins are used for
drainage calculations. The historic and developed basin boundaries
are to remain unchanged. The boundaries follow a slight ridge
along the edge of pavement to the north and south and are bounded
on the east by the car wash. The historic 100-year peak flow to
design point 1 is 3.6 cfs. The peak runoff for the developed
conditions will be the same.
420 S. Howes • Suite 202 • Fort Collins, Colorado 80521 • (303) 221-4158 • Fax (303) 221-4159
0
Spring Court Storage
Amended P.U.D.
Page 2
The Drainage Plan shows the project site within the floodplain
boundaries as determined by Engineering Professionals, Inc. in the
Spring Creek Master Drainageway Plan, March 1988. The floodplain
has been physically changed since then, but the maps have not been
updated yet. Therefore, special consideration will have to be made
for approval of the project.
Erosion Control during construction consists of roughening
bare soil and placement of gravel filters. when the pavement is
removed, roughening the bare soil, gravel filter dikes shall be
placed in the flowline to the existing inlets. After the new inlet
is rebuilt and the old one abandoned, a gravel inlet filter shall
be constructed around the new one and maintained until final
paving. The effeciency of these measures does not quite meet the
performance standard as calculated. A variance is requested due
to the nature of the project; it is small and the time that bare
ground is exposed during construction will be short. It seems
unreasonable to try and place erosion control on bare ground that
will immediately be built upon.
We would estimate the cost of erosion control to be
approximately $325.00 for the gravel filters. The cost of soil
roughening will be inherant to the asphalt removal.
If you should have any questions or comments as you review
this letter, please feel free to contact me at your earliest
convenience.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
EGI
Mary B. Wohnrade, I.p�;e�PE ✓O':e9'
Michael F. J ne . P.E. K*e . :.
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IREFERENCE:
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-641-
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Indicate by use of a bar line or symbols when erosion control measures will be installed.
Major modifications to an approved schedule may require submitting a new schedule for
approval by the City Engineer.
YEAR /'t ti4 .
MONTH IMAR- IAPR, IMar -3",4
OVERLOT GRADING
WIND EROSION CONTROL
Soil Roughening
Perimeter Barrier
Additional Barriers
Vegetative Methods
Soil Sealant
Other
RAINFALL EROSION CONTROL
STRUCTURAL:
Sediment Trap/Basin
Inlet Filters
Straw Barriers
Silt Fence Barriers
Sand Bags
Bare Soil Preparation
Contour Furrows
Terracing
Asphalt/Concrete Paving
Other
VEGETATIVE:
Permanent Seed Planting
Mulching/Sealant
Temporary Seed Planting
Sod Installation
Nettings/Mats/Blankets
Other
STRUCTURES: INSTALLED BY
VEGETATION/MULCHING CONTRACTOR
DATE SUBMITTED
MAINTAINED BY
APPROVED BY CITY OF FORT COLLINS ON
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