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FINAL DRAINAGE REPORT
FOR
MAPLE STREET APARTMENTS
CITY OF FORT COLLINS
STATE OF COLORADO
JANUARY, 1985
PROJECT NO.: 332.3
Prepared by:
Engineering Professionals, Inc.
2625 Redwing Rd., Suite 110
Fort Collins, CO 80526
(303) 226-3852
INTRODUCTION
This final drainage report is.submitted in conjunction with
construction drawings for Maple Street Apartments prepared by
Engineering Professionals, Inc. The City of Fort Collins "Storm
Drainage Design Criteria and Construction Standards" were used as
a guideline during the preparation of this report.
SITS DESCRIPTION
The Maple Street Apartments are located at 1216 Maple Street
in north -central Fort Collins, and are more particularly
described as part of lots 7 and 8 of the Tennyson Heights
subdivision. The site contains 22,000 square feet and slopes to
the north and west at approximately 1.3%. A portion of the site
is currently occupied by a single-family residence, while the
remainder of the site is vegetated by trees, shrubs and lawn. A
13-unit apartment building and parking lot are proposed for
construction on the site.
HISTORIC DRAINAGE
The site has historically drained to the north and west,
storm water leaving the site at the northwest corner of- the
property, crossing adjacent lands to the west and north, then
discharging to Cherry Street. Historic discharges from the site
are estimated to be .20 cfs and 0.70 cfs for the 2-year and 100-
year events, respectively. .
DRAINAGE UNDER DEVELOPED CONDITIONS
The historic site drainage pattern will not be altered by
development except for the addition of approximately 3400 cubic
feet of parking lot detention to meet City of Fort Collins Storm
' Drainage Design Criteria detention requirements. Storm water
developed on the site will flow through parking lot detention to
the northwest corner of the property. A valley pan will be
' installed from the northwest site corner to Cherry Street across
adjacent property to allow the storm water to discharge into
Cherry Street as it has done historically. Releases from the
' parking lot detention area will be limited to the 2-year historic
discharge of .20 cfs by a 2.76" orifice in a concrete headwall.
' We propose to use a 2-1/2" (nominal) schedule 40 PVC pipe as the
orifice. This .size of pipe has an inside diameter of 2.469
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inches, which closely approximates the required diameter of 2.76
inches. Maximum water depth in the detention area is .93 feet;
should the orifice plug, the top of the headwall will be set .93
feet above the orifice invert in order to act as an'overflow weir
to limit significant increases in water depth. Estimated
developed discharges are .84 cfs and 3.30 cfs for the 2-year and
100-year events, respectively.
MNS:psm
Respectfully submitted,
ENGINEERING PROFESSIONALS, INC.
Jonathan B. Howard
Michael N. Schmid, P.E.
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PROJECT NAME:
MAPLE_ (STREET
APARTMEN"fS
PROJECT NUMBER: 33L.3--111
DEVELOPED RATIONAL COEFFICIENT= .6'-9
BASIN AREA=
.51 ACRES
ALLOWABLE RELEASE RATE= .38 CFS/ACRE
INFLOW
OUTFLOW
DETENTION
TIME,
VOLUME,
VOLUME
VOLUME,
MINUTES
CU. FT.
CU. l=T.
CU. FT.
10
1900.26
1. 16. 28
1783.98
20
2744.82
C-3 .56
2512.26
30
3325.45
348.84
276.61
40
3694.95
465.12
3229.83
50
3958.67
581.4
3377.47
60
4117.23
697.68
3419.55
70
4249.19
31.3.96
3435.23
80
4328.37
930.24
3398.13
90
4441.85
1.046.52
3395.34
100
4486.72
1 1 [,2. 6
3323. 92
110
4557.98
1279.08
3278.9
120
4560.62
1395.36
3165.26
130
4563. 'PG
151. 1 . 64
3051.62
.140
4618.68
1627.9;'
2990.77
150
4711.06
1744.
2966. 86
160
4771.76
1860. 48
2911.281
170
4935.39
1. 976. 76
172958. 63
180
5083.19
2093.04
2990.11)
190
5014.57
32
2805.25
200
5120.14
2325.6
2794.54
210
5154.45
2441. 88
92712. 57
220
5225.71
2558.16
2667.55
230
52:81..14
2G74.44
2606.7
240
5320.73
2790.72
2530.01
250
5344.48
'c'907 '
2437.48
260
5421.02
3023.28
2297.74
270
5415.74
3139.56
22'76. 18
280
5394.62
3 '5 5. 84
2138. 78
290
5434. '.' 1
370i. 12
2062. 09
300
5463.24
:;488. 4
1974.85
310
5481. 72
.3G'Z14. E,8
1877.04
320
5489.64
3720.96
1.768.68
330
5487
38--;7. 24
1649. 76
340
5563. 54
L"'
1610. 02
350
5634.79
4069. 8
1 565
360
5510.75
4186.08
1324.67
REQUIRED DETENTION VOLUME, CU. = 3435.23