HomeMy WebLinkAboutDrainage Reports - 05/21/19903ras�,bnM� of ' �i�aQ
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STORM DRAINAGE REPORT�C .2
SPRINGBROOK P.U.D.
PREPARED FOR
MR. GARY MACKEY
APRIL 25, 1990
AS REVISF_U 5/1(f90
PREPARED BY
STEWART & ASSOCIATES, INC.
SITE LOCATION:
The site is located in the Northwest 4 of the Northwest '—, of Section
27, Township 7 North, Range 69 West of the Sixth P.M., Fort Collins,
Larimer County, Colorado. The site is bounded on the north by West Drake
Road, on the east by the constructed Georgetown Project, and undeveloped
on the west and south sides of the site. Spring Creek is adjacent to
the south side of the project. The site is shown on the vicinity map
at sheet 3 of this report.
SITE DESCRIPTION:
The site contains 6.28 gross acres. There is an existing house and shed
located in the Northwest part of the project. The majority of the site
is covered with grass type vegitation. There is a 21.5 foot driveway
access to a house south of the project'located along the east property
line of the site. The North 52 feet of Drake Road is constructed. The
south portion of the site is in the floodway of Spring Creek as shown
in the Spring Creek Master Drainageway Plan completed for the City of
Fort Collins by Engineering Professionals Inc., dated March, 1988. From
the City topography maps the site runoff is from the northwest to
southeast. The runoff in the southwest portion of the site is more to
the south. The slope of the site varies from 0.9% over the East z to
8.5% in the Southwest a. There is currently no offsite runoff across
the site. All runoff from the site is to Spring Creek. The existing
runoff from the site is Q2 = 2.55 c.f.s.; Q10 = 4.54 c.f.s.; Q100 = 9.69
c.f.s. more or less.
PROPOSED DESIGN:
The site will be subdivided into 21 lots, a street along the east side
of the site and a cul—de—sac running west to east in the middle of the
site. Drake Road will be constructed to arterial standards and the other
two to residential standards. The North 14 lots will be duplex lots
and the remaining 7 lots are single family lots. The existing house
is to remain.
There shall be no lots platted within the floodway. A11 houses in the
100 year flood plain will be required to have finished floor 12 feet
above the developed 100 year flood plain elevation. The Spring Creek
major drainageway will be used to determine this elevation. Due to the
close location of the site to Spring Creek we propose to not have any
detention.
The site has been divided into four sub —basins, as shown on the attached
map at sheet 11 of this report. Basin No. 1 is the rear yard of six
single family lots' along with Tract "B", which is that portion of the
subdivision within the floodway. The run—off quantities from Basin No.
1 are calculated on sheet 5 of this report. Run—off from Basin No. 1
is sheet flow directly into Spring Creek.
Springbrook P.M.
April 1990
Page 2
Basin No. 2 is the south 2 of Springbrook Court and the front of Lots
16, 17, 18, 19, 20 and 21. Calculation sheet 5 of this report shows
the run—off quantities from Basin No. 2. The 2 year run—off is 1.1
c.f.s., so the gutter capacity of Springbrook Court will not be exceeded.
The gutter capacity for Springbrook Court is calculated on sheet 8 of
this report.
Basin No. 3 is the duplex lots north of Springbrook Court along with
the north 2- of Springbrook Court. The calculations on sheet 6 show the
2 year run—off from this basin to be 2.8 c.f.s., so the gutter capacity
of Springbrook Court will not be exceeded.
Basin No. 4 is the south ? of Drake Road including.35 feet of pavement
and 35 feet of landscaping and walk from Springmeadows Lane to Taft Hill
Road. The calculated 10 year run—off from this basin is 5.8 c.f.s.,
per calculation sheet 6, and the allowable gutter capacity from
calculation sheet 7 is 19.5 c.f.s. Water from Basin No. 4 will turn
around the radius into the west gutter of Springbrook Lane. This flow
will not exceed the gutter capacity of Springbrook Lane from Drake Road
to Springbrook Court, and the combined 2 year flows of Basin 4 and Basin
3 across Springbrook Court can be carried by the 6 foot concrete pan.
The combined 2 year flow of Basins 4, 3 and 2, which is 7.2 c.f.s., will
meet at the southwest radius of Springbrook Lane and Springbrook Court.
This 7.2 c.f.s. will be carried by the west gutter of Springbrook Lane,
as calculated on sheet 9 of this report. The ow rom arger storms
may overtop the west curb and/or the centerline of the street. ,ELQw
that overto s the centerline can be carried by the east gutter, which
as no basin exce t t e east z of S rin rook Lane. ows which overtop
the west curb will go across ract "B", a green area, to Spring ree .
Sheet 11 of this report is the overall grading and drainage plan for
Springbrook P.U.D., and it shows all surface flows, both direction and
quantity.
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