HomeMy WebLinkAboutSTONEBRIDGE GARDEN APARTMENTS PRELIM PUD - 82 93 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTCOMPUTATION
James H. Stewart & Assoc.
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Fort Collins, Colorado
Sheet No. of
Job No.
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GENERAL LOCATION OF
COLLINDALE SOUTH POND
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Table 3.-
Summary of Storm Runoff Computations
for Coll indale South
Storm
return
Peak
Drainage area frequency
Land use
Area
% Perv.,
Rainfall
Runoff
flow
(ac.)
(in.)
(in.)
(cfs)
North area 2-yr.
Existing
160
100,
1.23
0.08
16
2-yr.
Developed
16.0 '•
54
1.23
0.59
120
100-yr.
Existing
160
100
3.15
1.73
280
100-yr.
Developed
160
54
3.15
2.32
540
South area 2-yr.
Existing
70.
100.
1.23
0.08
5
2-yr.
Developed
.70
.27 ...
1.23
0.83
60
100-yr. -
Existing
70.
100
3.15
1.73
100
100-yr.
Developed
70
27
3.15
2.62
210
1.. -5- RESOURCE COMULTMTS IHC
Table
1.
Pervious
Area for
North
Drainage
Proposed
land use
Area
%
Pervious
(ac.)
Single family
110
60
Multi -family
12 dwelling/ac.
10
50
Multi -family
20 dwelling/ac.
4
40
Industrial
20
30
Shopping
0.3
5
Park
8
90
Pond
8
0
Total -
.160
Table
2.
Pervious
Area for
South
Drainage
Proposed
land use
Area
%
Pervious
(ac.)
Multi -family
12 dwelling/ac.
11
50
Pervious x
area
41
3
1
4
0
5
0
54% pervious
Pervious x
area
8
Multi- amity
20 dwelling/ac. _ 14 40 8�
Industrial 23 30 10
Shopping 22 5 1
Total - 70 27% pervious
-4- RESOURCE COH U WTS INC
The northern portion of the site naturally drains into the pond --drainage
ways, as well as streets and storm sewers, will provide paths to the pond
from this area. One small area of proposed multi -family housing units
north and west of Lemay Avenue was assumed not to contribute storm water
runoff to the pond. This area will utilize a separate drainage plan.
There appears to be almost no contributions to the site drainage
from surrounding areas. The western boundary of the property is Lemay
Avenue and areas to the west drain south along Lemay to Harmony Road.
South of Harmony Road the drainage is southeasterly. North of the site is
the Collindale golf course, whose major drainage is north or into ponds
on the golf course.
The pond will consist of a small dam on the east side with the main
portion of the pond to be excavated. The source of water for the pond
will be drain tiles which currently originate on the property and surface
near the east property line. This water currently flows under the rail-
road through a 36-inch culvert located at the proposed outlet to the pond.
Runoff Computations
The site was divided into the two drainage areas (north and south)
for computational purposes. The existing land use on these areas was
assumed to be 100 percent pervious for each drainage area. The pervious
area was then determined for each drainage area based on the proposed land
use, and Tables 1 and 2 show these computations.
Hydrographs were computed for each drainage area with the 2-year and
100-year storm and for the existing and developed conditions utilizing
the Colorado Urban Hydrograph procedure. The results of the computations
are summarized in Table 3. The inflow hydrographs for the detention pond
are the summation of the hydrographs for the north and south areas. Figures
2 and 3 show the resulting inflow hydrographs for the 2-year and. 100-year
storms, respectively.
-3- RESOURCE COMULTMTS IriC
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FIGURE I SITE DRAINAGE. GoLPEN PA.EPPOW�
DESIGN HYDROLOGY
COLLINDALE SOUTH DETENTION POND
Introduction
The Collindale South detention pond is located in the Southeast 1/4,
NSection 31, T7N, R68W.' This pond, which will normally contain water,
will also act as a storm -water detention storage for the Collindale South
development located on 230 acres in the South 1/2 of Section 31. The
M general layout and site drainage is shown in Fig: 1. The pond is gener-
ally designed to release storm water at no greater rate than the existing
conditions. The pond will be adjacent to a proposed neighborhood park.
This park will provide additional detention storage for storms greater
than a 2-year frequency.
Criteria for Detention
Discussions with City of Fort Collins personnel have produced the cri-
teria for detention that the rate of release of runoff from the development
cannot exceed the peak runoff rates prior to development. This criteria
must be followed for both the 2-year and 100-year storms. The City has
also requested that computation of these rates be made by the Denver
Regional Council of Governments' Colorado Urban Hydrograph procedure.
Utilizing these criteria for release of storm water from detention, the.,
effects of increased runoff downstream•of the development will be minimized.
Site Conditions
+ The existing condition of the site is that of agricultural row crops.
Fig. 1 shows the proposed developed condition of the property. A pond
approximately 3 acres -in size will be constructed on the eastern boundary
of the property forrecreational and storm -water detention purposes. The
pond will be located in the low portion of the property in a natural drainage
swale which drains a major portion of the site.
The site is generally divided into two areas of drainage as shown on
Fig. 1. The southern drainage area naturally drains to the southeast.
Plans are to construct a drainage way which will carry the storm water
from this area north along the east property line into the detention pond.
-1- RESOURCE CONSULTANTS IIyC
APPENDIX
STEwART&A�60CIATES
103S.MELr
FORT CO 80521
PH. 93 1 FAX
gOLLINS,
Consulting Engineers and Surveyors
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STEWART&ASjOCIATES
Consulting Engineers and Surveyors
By: Date: Client:
Project: (--'[7 u r- r7 e
Subject:
103 S. MELD, ,A, FORT COLLINS, CO 80521
PH. 482-9331 FAX 482-9382
4f . Sheet No. of _
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Stonebridge Apartments at Courtney -Park East
Page 2
The composite C factor for the proposed Stonebridge site is 0.643, and
the calculated release and required detention volume are 2.3 c.f.s. and 53,999
cubic feet.
A variance will be requested from the storm drainage criteria because
the runoff from Wheaton Drive and Harmony Road cannot be routed through the
onsite Stonebridge detention ponding area. This runoff goes directly into
the major swale along Harmony Road via existing inlets and pipes.
EROSION CONTROL
I presume the entire site will be overlot graded to provide the building
pads, parking lots and ponding area. The installation of curbs should follow
immediately thereafter, and roadbase and pavement will soon follow. While
the utilities and curbs are being installed, the building foundations and slabs
will be under construction. It appears that the curbs, base course, and
building slabs will provide erosion control during the site development.
Sediment control, such as inlet filters, sediment traps, silt fences and straw
bale swale barriers, will be utilized during the construction period and until
vegetative erosion control is established.
The Stonebridge site is located in a moderate rainfall and wind erodibility
zone.
Q' FQ
Phillip V Robinson, P.E. & L.S. Z*� 4502
enclosures •
�'01rnmH11p
PRELIMINARY DRAINAGE REPORT
OF
STONEBRIDGE APARTMENTS
AT
COURTNEY PARK EAST
PROJECT LOCATION AND EXISTING CONDITIONS
Stonebridge Apartments at Courtney Park East is an 8.2 acre site located
north of Harmony Road and west of Wheaton Drive. The site is in the Golden
Meadows area and drains to the Golden Meadows regional detention pond. The
site is in the Fox Meadows drainage basin.
The adjacent streets, Harmony Road and Wheaton Drive, are fully
constructed, and all offsite drainage facilities are in place. The site drains
to Wheaton Drive and also to a major drain Swale which runs west to east along
the north side of Harmony Road. The runoff from Wheaton Drive goes into this
swale via catch basins and storm drain pipes. This major Swale carries runoff
east to the west side of the U.P. Railroad, and then it turns north along the
railroad and then dumps into the Golden Meadows regional pond. A map of the
Golden Meadows area which shows flow patterns is included with this report.
There is offsite drainage onto the site from the existing Courtney Park
development lying to the west. One point of offsite drainage is at the
southwest corner of the site where a 15—inch pipe from an existing detention
pond drains into the existing major swale running west to east across the site.
The other offsite runoff comes onto the west side of the site from 0.64 acres
of the rear yards of the Courtney Park apartments.
PROPOSED DEVELOPMENT AND DRAINAGE FACILITIES
The site will be developed with eight apartment buildings and the
accompanying parking and recreation facilities. The density will be
approximately 20 units per acre.
In 1978, Resource Consultants did a drainage study of the entire Golden
Meadows area, and a regional detention pond was constructed to handle runoff
from this area. Included with this report are Pages 1, 2, 3, 4, 5 and 6 of
this 1978 report along with a plan of the detention pond and a map of the entire
Golden Meadows area.
The Stonebridge Apartments site is located in the southwest corner of
the Golden Meadows site approximately 3000 feet from the regional detention
pond. All of the drainage facilities, piping and swales are in place between
Stonebridge and the pond, but these facilities are not adequate to carry the
entire 100—year runoff, so we plan to have onsite detention in the parking
lots and landscaped areas.
The 1978 Resource Consultants report considered this site to be 40 percent
pervious, which equates to a C factor of 0.60.
In the 1980 drainage report for Golden Meadows Fifth, a C factor of 0.5
was estimated for this Stonebridge site, along with a detention quantity of
1.2 acre feet and a release of 5.0 c.f.s.
PRELIMINARY DRAINAGE REPORT
OF
STONEBRIDGE APARTMENTS
AT
COURTNEY PARK EAST
FORT COLLINS, COLORADO
PREPARED
FOR
JUNGE/REICH/ASSOCIATES
PREPARED
BY
STEWART & ASSOCIATES, INC.
103 SOUTH MELDRUM STREET
FORT COLLINS, COLORADO 80521
303/482-9331
DECEMBER 6, 1993