HomeMy WebLinkAboutDrainage Reports - 03/01/1979 (2)DRAINAGE STUDY
LAKE STREET TOWNHOUSE P.U.D.
PREPARED FOR
LES KAPLAN, PLANNING CONSULTANT
528 S. Howes Street
Fort Collins, Colorado
PREPARED BY
JOE ROESSER, JR., P.E.
BRADFORD L. SMITH & ASSOCIATES
155 N. College Avenue
Fort Collins, Colorado
March 1979
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TABLE OF CONTENTS
EXISTING CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
PARAMETERS AND ASSUMPTIONS, DEVELOPED PROPERTY . . . . . .
. . . . . 2
AREA
I -
CALCULATIONS . . . . . . . . . . . . . . . . . . .
. . . . . . . . 3,4,5,6
AREA
II
- CALCULATIONS . . . . . . . . . . . . . . . . . .
. . . . . . ... 7,8,9,10
AREA
III
- CALCULATIONS . . . . . . . . . . . . . . . . . .
. . . . . . . . 11,12,13,14
AREA
IV
- CALCULATIONS . . . . . . . . . . . . . . . . . .
. . . . . . . . 15
AREA
V -
CALCULATIONS . . . . . . . . . . . . . . . . . . .
. . . . . . . . 16
EXISTING CONDITIONS
The property to be considered is a 3.345 acre tract located in the Southwest
1/4 of Section 14, Larimer County Colorado, and inside the City limits of Fort
Collins. The property is bounded on the north by West Lake Street, on the south
by Prospect Street, by Shields Street on the west, and at the dead end of Summer
Street on the west. A more particular description of the property is given by the
legal description for the West Lake Townhose P.U.D.
The existing ground cover is an open field, lightly vegitated throughout on
heavy soil; the north 2.5 acres slope on the average 1.75% from southwest to north-
east. Drainage is accomplished by way of the curb and gutter in West Lake Street.
The southern acre slopes on the average 2.5% from norhteast to southwest. Drainage
for this area is accomplished by way of the curb and gutter in Prospect Street.
-1-
ASSUMPTIONS AND PARAMETERS
DEVELOPED PROPERTY
Twenty townhouse units are planned for the 3.3455 acre parcel. A twenty-
five to forty foot wide street will provide access through the area, together with
off-street parking, roll-over curb, gutter and sidewalk. All open space will be
developed to include lawn and landscaped areas.
This drainage study has been prepared using the Storm Drainage Design Criteria
supplied by the City of Fort Collins (November 6, 197-8-), together with locally
accepted engineering principles, and information from Data Book for Civil Engineers
Vol. I by Elwyn Seelye.
For drainage purposes, the property will be divided into 3 areas. Areas I
and II will drain toward the north property boundary on West Lake Street, and Area
III toward the south property boundary on Prospect Street. Retainage will be accom-
plished in two open area basins near West Lake Street, and one open area near Pros-
pect Street. Drainage will be discharged, at the controlled rate, onto the south
curb and gutter on West Lake Street, and onto the north curb and gutter on Prospect
Street. Runoff will be collected from there by the City storm drainage system.
A small amount of runoff will flow onto the development from Areas V (south-
east) and Area1V (west). Provisions will be made to carry these flows along the
east and west property boundaries to the existing curb and gutter on West Lake
Street, and no provision will be made for retainage from these areas.
-2-
AREA I CALCULATIONS
AREA I + AREA II + AREA III = 145,730 ft2 = 3.3455 acres
2-Year Storm Runoff: Total Area = 53,582 ft2 = 1.229 acres
11C11
Open Field Light Vegitation, Heavy Soil 53,528 ft 2 .30
Tc (basin length = 350 ft, average slope = 1.7% = 24 minutes
I = 1.68 in/hr
Q = CIA = (.30)(1.68)(1.229) = .619 CFS
100-Year Storm Runoff:
1C11
Roof Area 16,989 ft2 .95
Street, Curb, Gutter and Sidewalk 10,254 ft2 .95
Established Lawn, Shrubbery 26,285 ft 2 .20
Factored "C" = •95(16,989 + 10,254) + .2(26,285) = 58
53,528
Tc (basin length 350 ft, average slope = 1.2%) = 17.2 minutes
I/ I = 5.6 in/hr
N
Q = CfCIA = 1.25(.58)(5.6)(1.229) = 4.989 CFS
For A ea I runoff outlet to West Lake Street, use:
„ -•1 t• - ryP
N04 SLID . n I
METAL Cb 2 6 x 6 concrete channel
TYP Fb� ALI - FL ° ? Q = .91 CFS
CorrG CNANNELS ° • 1111 1% Slope '
Iq T1415 ecPov-T = �\
ill=Ill- �5% coMP�L"ilohl �•Ur��oUN�lnIG CNA1,(N�t.•_
Required retention volume shown on graph.
-3-
TIME(MINUTES)
5
10
20
gif
40
50
60
70
80
90
100
110
120
130
Efdil
150
160
170
180
AREA I
2-YEAR STORM
(ft3 x 10-3)
(CA)(I)(SECONDS)
Volume
(.3687)(3.30)(300)
.36
(.3687)(2.50)(600)
.55
(.3687)(1.85)(1200)
.82
(.3687)(1.47)(1800)
.98
(.3687)(1.20)(2400)
1.06
(.3687)(1.05)(3000)
1.16
(.3687)(.82)(3600)
1.09
(.3687)(.73)(4200)
1.13
(.3687)(.68)(4800)
1.20
(.3687)(.62)(5400)
1.23
(.3687)(.57)(6000)
1.26
(.3687)(.52)(6600)
1.27
(.3687)(.50)(7200)
1.33
(.3687)(.46)(7800)
1.32
(.3687)(.43)(8400)
1.33
(.3687)(.42)(9000)
1.39
(.3687)(.40)(9600)
1.42
(.3687)(.39)(10,200)
1.47
(.3687)(.38)(10,800)
1.51
-4-
AREA I
100-YEAR STORM
(ft3 x 10-3)
TIME(MINUTES)
(CfCIA)(I)(SECONDS)
VOLUME
5
(.891)(8.50)(300)
2.27
10
(.891)(7.20)(600)
3.85
20
(.891)(5.10)(1200)
5.45
30
(.891)(4.20)(1800)
6.74
40
(.891)(3.50)(2400)
7.48
50
(.891)(3.00)(3000)
8.02
60
(.891)(2.60)(3600)
8.34
7.0
(.891)(2.30)(4200)
8.61
80
(.891)(2.05)(4800)
8.77
90
(.891)(1.85)(5400)
8.90
100
(.891)(1.70)(6000)
9.10
110
(.891)(1.55)(6600)
9.11
120
(.891)(1.45)(7200)
9.30
130
(.891)(1.30)(7800)
9.03
140
(.891)(1.25)(8400)
9.34
150
(.891)(1.20)(9000)
9.62
160
(.891)(1.10)(9600)
9.41
170
(.891)(1.05)(10,200)
9.54
180
(.891)(1.00)(10,800)
9.62
-5-
11
4
0
e
N
0 00 �9 �t N
�OLUNIC-(FT-IX to,)
AREA II CALCULATIONS
2-Year Storm Runoff: Total Area = 59,815 ft2 = 1.373 acres
Open Field, Light Vegitation,,Heavy Soil 59,815 ft2
Tc (basin length = 480 ft, average slope = 1.77%) = 28 minutes
I = 1.5 in/hr
Q = CIA = (.30)(1.5)(1.373) = .618 CFS
100-Year Storm Runoff:
Roof Area: 22,946 ft2
Street, Curb, Gutter and Sidewalk 10,725 ft2
Established Lawn, Shrubbery 26,144 ft2
Factored "C" = '95(22,946 + 10,725) + .2(26144) = 62
59,815
Tc (basin length 480 ft, average slope = 1.50%) = 18.8 minutes
I = 5.48 in/hr
Q = CfCIA = (1.25)(.62)(5.48)(1.373) = 5.83 CFS
For Area II runoff outlet to West Lake Street, use:
6 x 6 Concrete Channel
Seven #4 Rebar
1% Slope
Q = .91 CFS
illl �IIII = �---_— 95'`7� CaMP/1C,Tro;.1 sur_�:ov�ly' �ti�l� CNAt�lNEl_
Required retention volume shown on graph.
11C11
.30
11C11
.95
.95
.20
-7-
AREA II
2-YEAR STORM
3 3
(fO )
TIME(MINUTES)
(CA)(I)(SECONDS)
VOLUME
5
(.41)(3.30)(300)
.41
10
(.41)(2.50)(600)
.61
20
(.41)(1.85)(1200)
.91
30
(.41)(1.47)(1800)
1.09
40
(.41)(1.20)(2400)
1.19
50
(.41)(1.05)(3000)
1.30
60
(.41)(.82)(3600)
1.22
70
(.41)(.73)(4200)
1.26
80
(.41)(.68)(4800)
1.34
90
(.41)(.62)(5400)
1.37
100
(.41)(.57)(6000)
1.40
110
(.41)(.52)(6600)
1.41
120
(.41)(.50)(7200)
1.48
130
(.41)(.46)(7800)
1.47
140
(.41)(.43)(8400)
1.48
150
(.41)(.42)(9000)
1.55
160
(.41)(.40)(9600)
1.57
170
(.41)(.39)(10,200)
1.63
180
(.41)(.38)(10,800)
1.68
-n-
AREA II
100-YEAR STORM
(ft3 x 10-3)
TIME(MINUTES) (CfCIA)(I)(SECONDS) VOLUME
5
(1.06)(8.50)(300)
2.70
10
(1.06)(7:20)(.600)
4.58
20
(1.06)(5.10)(1200)
6.48
30
(1.06)(4.20)(1800)
8.01
40
(1.06)(3.50)(2400)
8.90
50
(1.06)(3.00)(3000)
9.54
60
(1.06)(2.60)(3600)
9.92
70
(1.06)(2.30)(4200)
10.24
80
(1.06)(2.05)(4800)
10.43
90
(1.06)(1.85)(5400)
10.59
100
(1.06)(1.70)(6000)
10.81
110
(1.06)(1.55)(6600)
10.84
120
(1.06)(1.45)(7200)
11.07
130
(1.06)(1.30)(7800)
10.75
140
(1.06)(1.25)(8400)
11.13
150
(1.06)(1.20)(9000)
11.45
160
(1.06)(1.10)(9600)
11.19
170
(1.06)(1.05)(10,200)
11.35
180
(1.06)(1.00)(10,800)
11.45
-9-
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VOLUME
802
AREA III CALCULATIONS
2-Year Storm Runoff: Total Area 32,387 ft2 =
Open Field, Light Vegitation, Heavy Soil
.74 acres
C"
32,387 ft 2 .30
Tc (basin length = 250 ft, average slope = 3%) _
1.87(1.1 - C) D = 1.87(1.1 - .3)(250) = 16.4 minutes
S (3)
I'= 2.05 in/hr
Q = CIA = (.30)(2.05)(.74) _ .46 CFS
100-Year Storm Runoff:
Roof Area
Street, Curb, Gutter and Sidewalk
Established Lawn, Shrubbery
Factored C. _-.95(8933 + 7392) + .2(16062) = 59
32,387
Tc (basin length = 285 ft, average slope = 2.8%) _
1.87(1.1 - .59)(285) = 11.42 minutes
(2.8)
I = 6.75 in/hr
Q = CfCIA = 1.25(.59)(6.75)(.74) = 3.68 CFS
For Area III outlet to curb and gutter on Prospect Street, use:
2" Z„
Ilii =1111
8,933 ft2
1C11
7,392 ft2
.95
2
.95
16,062 ft
.20
6 x 4 Concrete Channel 1% Slope
Seven #4 Rebar
Non -Slip Metal Cover
50L7F %'g"x 2° STEEL STrzAP TD Lo&IL
WELE;�y4° IIIETAL Co✓EQ:. TO STZA'
IIII
��9�'Io Coi�APAc;i�o.1 SUE'E OUtJvIn1G GN1_\NnlEL
Required retention shown on graph.
-11-
AREA III
2-YEAR STORM
O-3)
(f
TIME(MINUTES)
(CA)(I)(SECONDS)
VOLUME
5
(.2220)(3.30)(300)
.22
10
(.2220)(2.50)(600)
.33
20
(.2220)(1.85)(1200)
.49
30
(.2220)(1.47)(1800)
.59
40
(.2220)(1'.20)(2400)
.64
50
(.2220)(.1.05)(3000)
.70
60
(.2220)(.82)(3600)
.66
70
(.2220)(.73)(4200)
.68
80
(.2220)(.68)(4800)
.72
90
(.2220)(.62)(5400)
.74
100
(.2220)(.57)(6000)
.76
110
(.2220)(.52)(6600)
.76
120
(.2220)(.50)(7200)
.80
130
(.2220)(.46)(7800)
.80
140
(.2220)(.43)(8400)
.80
150
(.2220)(.42)(9000)
.84
160
(.2220)(.40)(9600)
.85
170
(.2220)(.39)(10,200)
.88
180
(.2220)(.38)(10,800)
.91
-12-
AREA III
100-YEAR STORM
(ft3 x 10-3)
TIME(MINUTES)
(CfCIA)(I)(SECONDS)
VOLUME
5
(.5458)(8.50)(300)
1.39
10
(.5458)(7.20)(600)
2.36
20
(.5458)(5..10)(1200)
3.34
30
(.5458)(4.20)(1800)
4.13
40
(.5458)(3.50)(2400)
4.50
50
(.5458)(3.00)(.3000)
4.91
60
(.5458)(2.60)(3600)
5.11
70
(.5458)(2.30)(4200)
5.27
80
(.5458)(2.05)(4800)
5.37
90
(.5458)(1.85)(5400)
5.45
100
(.5458)(1.70)(6000)
5.57
110
(.5458)(1.55)(6600)
5.58
120
(.5458)(1.45)(7200)
5.70
130
(.5458)(1.30)(7800)
5.53
140
(.5458)(1.25)(8400)
5.73
150
(.5458)(1.20)(9000)
5.89
160
(.5458)(1.10)(9600)
5.76
170
(.5458)(1.05)(10,200)
5.85
180
(.5458)(1.00)(10,800)
5.89
-13-
S Ul ^� �o N —
VOLUME Fr3x10-��
-14-
0
ADPA T11
Runoff from Area IV during the 100-Year Storm will be collected and carried
in a swale along the northwest property boundary.
Total Area = 37,200 ft2 = .854 acres
Use C = .5 (residential)
Tc (basin length = 300 ft, average slope = 2%) = 16 minutes
I = 5.8 in/hr
Q100 = CfCIA = (1.25)(.5)(5.80)(.854) = 3.10 CFS
Channel A characteristics: average available slope = 2%
At 2%, sodded channel, Q = 4.7 CFS
Velocity = 2.8 ft/sec
2" -0 MIMuM
i
-15-
nnrn v
Runoff from Area V during the 100-Year Storm will be collected and
carried by a channel along the southeast and east property boundaries.
Total Area = 19,800 ft2 = .454 acres
Use C = .5 (residential)
Tc (basin length = 250 ft, average slope = 2%) = 17 minutes
I = 5.7 in/hr
Q100 = CfCIA = (1.25)(:5)(5.,7)(:454) = 1.62 CFS
Channel C characterisitics: average available slope = 2%
f�
3.0 —
,OD MIKIIh1UM
Q = 3.5 CFS (approximately)
V = 3.5 = 3 ft/sec (approximately)
12
Channel B characteristics: (east catch basin to Area II retainage basin)
Imo_ 5,001
soil
2"Sor>- INIhIIMUM
-Im_Ipllu�
Q (capacity) = 4.5 CFS (1% slope)
-16-
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BRADFORD L SMITH A ASSOC.
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