HomeMy WebLinkAboutLINDEN GROVE PUD - PRELIMINARY - 49-94 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTTABLE 2. ESTIMATED REQUIRED DETENTION
(DETAIN THE DEVELOPED 100-yr STORM AND RELEASE AT THE 10-yr HISTORIC RATE)
PO NO 02-
,Qin=
C(Cf)IA=
21.241
. . . . . . . . . . . .
... .....
...............
.1 . . ...
.......
. I . . . . . . . . . . . . . . . . . .......
. .........
elm
10
7.00
148.68
89,208
10.50
6,300
82,908
20
5.10
108.32
129,989
10.50
12,600
117,389
30
4.10
87.08
156,751
10.50
18,900
137,851
40
3.50
74.34
178,416
10.50
25,200
153,216
50
3.00
63.72
191,160
10.50
31,500
159,660
60
2.65
56.29
202,630
10.50
37,800
164,830
70
2.40
50.98
214,099
10.50
44,100
169,999
80
2.20
1 46.73
224,294
10.50
50,400
173,894
90
1.95
41.42
223,657
10.50
56,700
166,957
100
1.80
38.23
229,392
10.50
63,000
166,392
110
1.60
33.98
224,294
10.50
69,300
154,994
1 120
1.50
31.86
229,392,
10.50
75,600
153,792
TST, INC.
CONSULTING
ENGINEERS
8
9/9/94
1 0
TABLE 2. ESTIMATED REQUIRED DETENTION
(DETAIN THE DEVELOPED 100-yr STORM AND RELEASE AT THE 10-yr HISTORIC RATE)
IPOND "I
Qin= C(COIA=
9.39 1
ON
10
7.00
65.73
39,438
0.65
390
39,048
20
5.10
47.89
57,467
0.65
780
56,687
30
4.10
38.50
69,298
0.65
1,170
68,128
40
3.50
32.87
78,876
0.65
1,560
77,316
50
3.00
28.17
84,510
0.65
1,950
82,560
60
2.65
24.88
89,581
0.65
2,340
87,241
70
2.40
22.54
94,651
0.65
2,730
91,921
80
2.20
20.66
99,158
0.65
3,120
96,038
90
1.95
18.31
98,877
0.65
3510
95,367
100
1.80
16.90
101,412
0.65
3:900
97,512
110
1.60
15.02
99,158
0.65
4,290
94,868
1 120
1.50
14.09
.101,412
0.65
4,680
96,732
TST, INC.
CONSULTING
ENGINEERS
7
9/9/94
TABLE 1. HYDROLOGIC CALCULATIONS WORKSHEET
(DEVELOPED ON SITE AND EXISTING OFFSrfE CONDITION)
YrrER
.
.. .......
T. A.M.
RASIN;::�'
NY
ft -M,
......
1
0
0.60
2.12
0.00
21.05
17.41
3.15
5.55
5.95
13.11
Bi
2
400
0.60
2.12
3.15
15.30
13.20
3.70
6.30
1.91
4.08
B2
2
350
0.60
2.12
2.75
14.91
12.80
3.73
6.50
1.44
3.14
B
IR3
2
1050
0.60
2.12
8.26
20.41
18.31
3.18
5.40
6.01
12.76
B4
2
1000
0.60
2.12
7.86
20.02
17.92
3.23
5.50
4.35
9.25
B5
2
700
0.60
2.12
5.50
17.66
13.56
3.45
5.90
5.22
11.15
cl
3
300
0.60
2.12
2.36
14.51
12.41
3.75
6.50
1.87
4.06
C
C2
3
350
0.60
2.12
2.75
14.91
12.80
3.73
6.50
2.30
5.01
C3
3
500
0.60
2.12
3.93
116.09
13.98
3.61
6.20
1.88
4.05
C4
2
450
0.60
2.12
3.54
15.69
13.59
3.68
6.45
1.42
3.12
DI
4
150
0.60
2.12
1.18
13.33
11.23
3.90
6.85
0.89
1.93
D2
4
150
0.60
2.12
1.18
13.33
11.23
3.90
6.85
0.84
1.85
D3
5
350
0.60
2.12
2.75
14.91
12.80
3.73
6.50
2.00
4.35
D
D4
5
500
0.60
2.12
3.93
16.09
13.98
3.61
6.20
2.62
5.61
D5
6
600
0.60
2.12
4.72
16.87
14.77
3.53
6.08
2.78
5.99
D6
6
550
0.60
2.12
4.33
21.52
18.54
3.10
5.40
6.31
13.73
D7
7
450
0.60
2.12
3.54
15.69
13.59
3.68
6.45
3.23
7.07
D8
6
1250
0.60
2.12
9.83
21.99
19.88
3.08
5.20
6.24
13.16
El
8
600
0.60
2.12
4.72
21.91
18.93
3.08
5.35
4.14
0.00
E2
9
800
0.60
2.12
6.29
23.48
20.51
2.98
5.15
3.16
6.84
E
E3
8
1000
0.60
2.12
7.86
25.05
22.08
2.86
4.96
6.51
14.12
E4
a
1100
0.60
2.12
8.65
20.81
18.70
3.13
5.40
3.41
7.35
ES
8
1100
0.60
2.12
8.65
20.81
18.70
3.13
5.40
5.44
11.72
TST, INC.
CONSULTING
ENGINEERS
j
9/8/94
c M,
7-MIRMIMIMMIMIRIMIEW.
TABLE 1. HYDROLOGIC CALCULATIONS WORKSBEET
(DEVELOPED ON SITE AND EXISTING OFFSITE CONDITION)
............VER%iSiSiB.....
............
ch
ASIN
A
1
4.20
0.45
1.00
1.25
1.89
2.36
300
1.00
21.05
17.41
B1
2
1.15
0.45
1.00
1.25
0.52
0.65
100
1.00
12.16
10.05
B2
2
0.86
0.45
1.00
1.25
0.39
0.48
100
1.00
12.16
10.05
B
B3
2
4.20
0.45
1.00
1.25
1.89
2.36
100
1.00
12.16
10.05
B4
2
2.99
0.45
1.00
1.25
1.35
1.68
100
1.00
12.16
10.05
B5
2
3.36
0.45
1.00
1.25
1.51
1.89
100
1.00
12.16
10.05
Cl
3
1.11
0.45
1.00
1.25
0.50
0.62
100
1.00
12.16
10.05
C
C2
3
1.37
0.45
1.00
1.25
0.62
0.77
100
1.00
12.16
10.05
C3
3
1.16
0.45
1.00
1.25
0.52
0.65
100
1.00
12.16
10.05
C4
2
0.86
0.45
1.00
1.25
0.39
0.48
100
1.00
12.16
10.05
D1
4
0.50
0.45
1.00
1.25
0.23
0.29
100
1.00
12.16
10.05
D2
4
0.48
0.45
1.00
1.25
0.22
0.27
100
1.00
12.16
10.05
D3
5
1.19
0.45
1.00
1.25
0.54
0.67
100
1.00
12.16
10.05
D
D4
5
1.61
0.45
1.00
1.25
0.72
0.91
100
1.00
12.16
10.05
D5
6
1.75
0.45
1.00
1.25
0.79
0.98
100
1.00
12.16
10.05
D6
6
4.52
0.45
1.00
1.25
2.03
2.54
200
1.00
17.19
14.21
D7
7
1.95
0.45
1.00
1.25
0.88
1.10
100
1.00
12.16
10.05
D8
6
4.50
0.45
1.00
1.25
2.03
2.53
100
1.00
12.16
10.05
El
8
2.99
0.45
1.00
1.25
1.35
1.68
200
1.00
17.19
14.21
E2
9
2.36
0.45
1.00
1.25
1.06
1.33
200
1.00
17.19
14.21
E
E3
8
5.06
0.45
1.00
1.25
2.28
2.85
200
1.00
17.19
14.21
E4
8
2.42
0.45
1.00
1.25
1.09
1.36
100
1.00
12.16
10.05
E5
8
3.86
0.45
1.00
1.25
1.74
2.17
100
1.00
12.16
10.05
TST, INC.
CONSULTING
ENGINEERS
5
9/8/94
C
3.2 Drainage Plan Development
The proposed drainage plan consists of overland flow across lots which will be collected in the
streets, directed to a detention pond then to the proposed Dry Creek Channel. Gutter flow in
streets will be collected at low points via curb inlets, piped to the detention pond, then outlet to
Dry Creek Channel. Subbasins were delineated based on a preliminary proposed grading plan.
The proposed grading is not shown on the Preliminary Drainage Plan; however, it is a
conservative assumption assuring that the streets will not be inundated. The results of the
hydrologic analysis can be found in Table 1 with supporting calculations shown in Appendix A.
Table 2 depicts the estimated detention requirements based on the weighted runoff rate found in
the Drainage Master Plan. Supporting information for the detention requirements can be found
in Appendix B.
The Final Drainage Report shall include an analysis of street capacities to determine if curb inlets
and storm sewers will be necessary at points further upstream than the low points. Curb inlets,
channels, culverts, and detention facilities will be sized to intercept and convey runoff from the
100-year storm. Channels, roadside ditches, and detention facilities will be designed to
incorporate a minimum of V of freeboard and will have velocities that do not promote erosion.
3.3 Erosion Control Plan
An erosion control plan will be submitted with the Final Drainage Report. Quantities and types
of erosion control measures to be used will be delineated in the Final Drainage Report.
TST, Inc. September 12, 1994
1a793-" 4
3.0 DEVELOPED CONDITIONS PLAN
3.1 Design Criteria
The drainage system presented in this report has been developed in accordance with the
guidelines established by the Fort Collins Storm Drainage Design Criteria and Construction
Standards (S.D.D.C.), and the Denver Regional Council of Government Urban Storm Drainage
Criteria Manual (USDCM).
Developed condition storm facilities were evaluated based on the 100-year storm frequency.
Since a Drainage Master Plan for the area has been completed, we followed the Master Plan's
guidelines; therefore, historic runoff was not calculated.
Due to the limited size of the site, the Rational Method was. selected to calculate runoff for street
capacity analysis. The Rational Method utilizes the S.D.D.C. Manual Equation:
Q = Cf CIA
where Q is the flow in CFS, A is the total Area of the basin in acres, Cf is the storm frequency
adjustment factor, C is the runoff coefficient, and I is the rainfall intensity in inches per hour.
The runoff coefficient, C, was selected to be 0.45 as taken from the S.D.D.C. Manual for RLP
zoning. The frequency adjustment factor, Cf, is given on pages 3-5, Table 3-4 of the S.D.D.C.
Manual and is 1.25 for the 100-year storm and 1.00 for the 2-year storm. The intensity (I) was
taken rom the City of Fort Collins rainfall intensity duration curve in the S.D.D.C. Manual. To
obtain the rainfall intensity, the time of concentration had to be determined.. The following
equation was utilized to determine the time of concentration:
4=k+tt
where t, is the time of concentration in minutes, t; is the initial or overland flow time in minutes,
and t� is the concentrated flow time (ditch, channel, or gutter) in minutes. The initial or overland
flow time was calculated using the equation on pages 3-5, section 3.1.7 in the S.D.D.C. Manual:
t;= 1.87(1.1-CCfLD!
S%
where t; is the initial time of concentration, D is the length of the overland flow in feet, S is the
average basin overland slope in percent. This procedure for computing time of concentration
allows for overland flow as well as travel time for runoff collected in streets, gutters, channels,
pipes, or ditches. The times of concentration calculated assumed only about 100 feet overland
flow of the total travel length. The remainder'of the flow was considered as channel flow (in
street gutters).
TST, Inc. September 12, 1994
10-793-" 3
io
11
1.0 INTRODUCTION
1.1 Scope and Purpose
This report presents the results of a Preliminary Drainage Evaluation for the Linden Grove
P.U.D. A hydrologic analysis of the proposed development plan was completed to determine
the location and magnitude of the storm runoff. A preliminary evaluation of major runoff
conveyance elements was conducted to determine approximate channel size, culvert sizes, and
detention pond sizes.
The purpose of this report is to evaluate the development in preparation for a final stormwater
management plan that will address: (1) overall storm drainage planning and management, (2)
detention facilities size and location, and (3) erosion control.
1.2 Project Location and Description
Linden Grove P.U.D. is a proposed residential site located in the Southeast Quarter of Section
1, Township 7 North, Range 69 West, of the 6th Principal Meridian, in Larimer County,
Colorado. The site is roughly bounded by North Lemay Avenue to the East, Redwood Street
to the West, East Vine Drive to the South, and Conifer Street to the North (see Figure 1). The
proposed site falls within the Evergreen-Greenbriar Drainage Basin.
Linden Grove P.U.D.. consists of 58.71 acres (more or less) and is within an RLP (Residential
Low Density) Zoning District within the City of Fort Collins, Colorado. The development will
have approximately 1R9 lots. All of the roadways within the development will be classified as
local streets.
1.3 Previous Studies
The "Evergreen-Greenbriar North Alta Vista Basin Drainage Master Plan" (draft copy by
Lidstone and Anderson, Inc:, September 1994) was reviewed prior to commencement of this
report. It was found that our site is only able to outlet 0.19 cfs per acre (11.15 cfs for entire
site).
2.0 HISTORIC CONDITIONS
The existing site, which is currently a farm field, has storm runoff which sheet flows to the
Southeast corner of the property. No offsite flow is conveyed across proposed site (it is collected
in Lake Canal Ditch).
TST, Inc. September 12, 1994
10-793-" 1
L
u
TABLE OF CONTENTS
1.0 Introduction Pare
1.1 Scope and Purpose ................................... 1
1.2 Project Location and Description .......................... 1
1.3 Previous Studies .................................... 1
2.0 Historic Conditions ....................................... 1
3.0 Developed Conditions Plan
3.1 Design Criteria .............. 3
3.2 Drainage Plan Development ............................. 4
3.3 Erosion Control Plan ................................. 4
Figures
Figure 1 - Vicinity Map ........................................ 2
Tables
Table 1 - Hydrological Calculations Worksheet ........................... 5
Table 2 - Estimated Required Detention ............................... 7
Technical Appendix
Appendix A -Rational Method Analysis
Appendix B - Preliminary Detention Analysis
TST, Inc. September 12, 1994
10-793-000 ii
n
a''
TSTI
Mr. Glen Schleuter
City of Fort Collins
Stormwater Utility
235 Mathews Street
P.O. Box 580
Fort Collins, CO 80522
Re: Linden Grove P.U.D.
Project No. 10-793-000
Dear Glen:
September 12, 1994
We are pleased to submit this Preliminary Drainage Report for Linden Grove P.U.D. This
report was prepared based on the City of Fort Collins criteria and we believe it satisfies all the
criteria set forth for a Preliminary Report.
If you should have any questions and/or comments, please do not hesitate to contact me.
Respectfully,
TST, INC., CONSULTING ENGINEERS
A�-4 -
Steve F. Humann, P.E.
MBR/lg
Enclosure
Michael B. Reeve, P.E.
TSTINC. 748 Whalers Way - Building D 102 Inverness Terrace East
! Fort Collins, CO 80525 Suite 105
Consulting Engineers (303) 226-0557 Englewood, CO 80112
Metro Denver (303) 595-9103 (303)792-0557
Fax (303) 226-0204 Fax (303) 792-9489
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