HomeMy WebLinkAboutDrainage Reports - 05/10/1991Gives-,� ,2�oer
OVERLAND HILLS SECOND FILING
FINAL DRAINAGE REPORT
PREPARED
FEBRUARY 6. 1991
PREPARED BY
STEWART & ASSOCIATES. INC.
SITE LOCATION:
The site is located in the Northwest a of Section 33, Township 7 North, Range 69 West
of the Sixth P.M., Fort Collins, Larimer County, Colorado. The area is 9.1916 acres
more or less. It is located in the Spring Creek Drainage Basin.
EXISTING CONDITIONS:
The site is bounded on the East by Tract A, Springfield Sixth Filing, which is a
detention pond. The outlet swale from this detention pond flows across our property
to Spring Creek. The Swale has been relocated to fit the final design of our
subdivision. The new swale will be 10 feet South of the South right—of—way line of
Horsetooth Road. The site is bounded on the South by an existing single family
residence and a portion of the Overland Hill First proposed subdivision. There is
no development on the West or North side. The site drains South to North and then
West to the Spring Creek Drainageway. Spring Creek Drainageway is along our West
property line. It is a non —improved channel that flows from the South to the North.
The drainageway North of our property has been regraded for farming. This will have
to be revised to allow for water to again flow in the drainageway. Springfield owners
are presently working to resolve this problem. There is an existing farm road into
the single family home South of our property. This entrance will be replaced by the
streets developed in Overland Hills First Filing. The site has an average slope of
about 1.6%. There is no offsite drainage from the North, East or West sides of this
proposed site. There will be some offsite flows from the existing single family
residence to the South. This offsite drainage flows to Spring Creek across the back
of Lot 4 and is not routed through our street system. This area is minimal and has
little effect on our developed site. There will not be any runoff from Overland Hills
First Filing. That water is rerouted to pass through the Springfield Detention Pond.
The existing site runoff to Spring Creek is Q2 = 2.7 c.f.s., Q10 = 5.1 c.f.s and Q100
= 10.3 c.f.s.
DEVELOPED CONDITIONS:
The proposed site will be divided into 4 lots served by a cul—de—sac from Horsetooth
Road. The average size lot will be about 2.3 gross acres. Because of the proximity
to Spring Creek Drainageway there will be no detention for these 4 lots. Tract "A"
has been platted and will be deeded to the City for drainage and trail use. The Spring
Creek 100 year floodway lies in this tract. The site is divided into Basin "A" and
Basin "B". All of the runoff from Basin "A" flows directly to Spring Creek
drainageway. The discharges from Basin "A" are Q = 1.01 c.f.s., Q1 = 1.80 c.f.s.
and Q700 = 3.61 c.f.s. The runoff from Basin "B" flows to the curb inlet shown on
Horsetooth Road. The discharges from Basin "B" are Q2 = 5.28 c.f.s., Q10 = 9.57 c.f.s.
and Q1np = 18.92 c.f.s. An 8.0 foot wide curb inlet is required on Horsetooth Road
to handle the 10 year flows. The South one half of Horsetooth Road can handle 6 c.f.s.
which exceeds the developed 2 year flow.
The 100 year floodway line and the 100 year floodplain line shown on the enclosed
drawing were taken from the "Floodplain Analysis for Overland Hills Subdivision" 'for
Filings 1 and 2 completed this year and revised by Resource Consultants, Inc. on
January 18, 1991. We are including with this report a copy of the outflow from the
detention pond on Tract "A" of Springfield Sixth Filing. An easement has been granted
from Kim Stuart to the Springfield Homeowners Association for this outflow swale.
Also included is a plan of the downstream outfall across the a'�£al t,IA�d of David and ?
Mary Whitham. Negotiations are underway at this time to $"er�axee� A qItitfall easement.-).
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✓� � � ��4Cr` °°°�GISTER•O° so 7� �G
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Franklin D. Blake, P.E. & L.S. F"} ;y 7839
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COMPUTATIONS
Stewart & Associates, Inc. 214 N. Howes St. Ft. Collins, CO 80521 (303) 482.9331
By: Date Client: Sheet No.- _of�_
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