HomeMy WebLinkAboutAccess Drive - Drainage LetterKLING ENGINEERING & SURVEYING
A Division of Civil Engineering Consultants
4101 Texas Avenue, Suite A
Bryan, Texas 77802
Telephone 979/846-6212
Fax 979/846-8252
S.M. Kling, R.P.L.S.
Fred Paine, P.E., CFM
September 7, 2012
To: City of College Station, Development Engineering
c/o Erika Bridges, Engineer
From: Fred Paine, P.E.
Re: Lots 9 & 10, Block 3, Tower Point Phase 11B
Access Drive - Drainage Letter
Post Office Box 4234
Bryan, Texas 77805
As a result of the proposed access drive construction, revisions to the existing storm sewer system are
required. The purpose of this memo is to document the proposed storm sewer revisions will be
consistent with existing conditions and to document the capacity of the proposed additional run of
storm sewer connecting pipe.
Storm Sewer Inlets:
Existing Conditions
Approximate Station 0+20 / 18' left
Width of depressed gutter - 2'
Gutter depression - 4" (assumed)
Length of curb opening - 5'
Street longitudinal slope - 1.2%
Street cross slope - 2.7%
per the access drive plan (Inlet 1):
Approx. Drainage Area: 0.124 ac w/ Tc <10 min; 10 min used
Assumed full development C-factor 0.90 (grassed median removed)
Approximate Station 2+18 / 9' right per the access drive plan (Inlet 2):
Width of depressed gutter - 2'
Gutter depression - 4" (assumed)
Length of curb opening - 5'
Street longitudinal slope - 1.6%
Street cross slope - 3.0%
Approx. Drainage Area: 1.196 ac w/ Tc <10 min; 10 min used
C-factor(ave): 0.84
Proposed Conditions
Approximate Station 0+20 / 60' right
Width of depressed gutter - 2'
Gutter depression - 4"
Length of curb opening - 5'
Street longitudinal slope - 1.3%
Street cross slope - 3.1%
per the access drive plan (Inlet 1R):
Approx. Drainage Area: 0.124 ac w/ Tc <10 min; 10 min used
Assumed full development C-factor 0.90 (grassed median removed)
pg 1 of 3
Proposed Conditions - continued
Approximate Station 2+32 / 36' left per the access drive plan (Inlet 2R):
Width of depressed gutter - 2'
Gutter depression - 4"
Length of curb opening - 5'
Street longitudinal slope - 1.6%
Street cross slope - 3.0%
Approx. Drainage Area: 1.196 ac w/ Tc <10 min; 10 min used
C-factor(ave): 0.84
The rational method was used to estimate the stormwater gutter flows. Based on the short time of
concentration, the 25 year rainfall intensity is calculated to be 9.86 in/hr.
The following table summarizes gutter flows & inlet capacities for the 25 year event.
Inlet
Q25
(cfs)
Gutter Flow
Water Spread
(ft)
Gutter Flow
Depth
(ft)
Length of
Curb Inlet
(ft)
Intercepted
Flow
(cfs)
Carry Over
(cfs)
1
1.16
5.9
0.22
5
1.04
0.12
1R
2.84
7.63
0.29
10
2.72
0.12
2
9.91
11.98
0.42
5
3.22
6.69
2R
9.91
11.98
0.42
5
3.22
6.69
Table 1
Inlets at the existing inlet locations will be converted to grate inlets with the tops set at proposed
finished driveway grade. The grates chosen are pedestrian safe and therefore provide little runoff
interception. Grate capacity was considered insignificant and therefore not included in capacity
calculations.
Storm Sewer Pipe:
The relocated inlet at approximate station 2+32 / 36' left will require a connecting pipe to the
converted grate inlet. The connecting pipe will be an 18" RCP installed at 7%. Capacity of the
proposed 18" connecting pipe is 27.8 cfs, contributing runoff is 3.22 cfs (portion of runoff intercepted
by inlet 2R).
pg 2 of 3
Conclusions:
The relocated inlets provide for the same runoff interception as the existing conditions inlets. The
connecting storm sewer pipe from relocated inlet 2R to existing inlet 2 is adequate to convey the storm
water runoff received by inlet 2R. No adverse affects are anticipated upstream or downstream due to
the storm sewer revisions.
Certification:
This report & plan for the drainage design of the Tower Point Phase 11 B, Lots 9 & 10 access drive
was prepared under my supervision in accordance with the provisions of the Bryan / College Station
Unified Drainage Design Guidelines for the Owners of the property. All licenses and permits required
by any and all state and federal regulatory agencies for the proposed drainage improvements have been
issued.
•
ALFRED A. PAINE
97221
State of Texas No.: 97221
Texas Engineering Firm No. F-2214
pg3of3
Gutter Flow - Inlet 1 - 25 yr
Worksheet for Irregular Channel
Project File
h:\ei6lrv-4\tpfrn7-2\p506ga-u\atfgn9-b\street.fm2
Worksheet
1/2 STREET SECTION -INLET 1-EXISTING
Flow Element
Irregular Channel
Method
Manning's Formula
Solve For
Water Elevation
Input Data
Channel Slope 0.012000 ft/ft
Elevation range: 300.73 ft to 301.50 ft.
Station (ft) Elevation (ft) Start Station End Station Roughness
-11.50 301.50 -11.50 12.50 0.013
0.00 301.23
1.00 301.23
1.00 300.73
2.00 300.82
12.50 301.10
Discharge 1.16 cfs
Results
Wtd. Mannings Coefficient
0.013
Water Surface Elevation
300.95
ft
Flow Area
0.50
ft?
Wetted Perimeter
6.12
ft
Top Width
5.90
ft
Height
0.22
ft
Critical Depth
300.98
ft
Critical Slope
0.005641 ft/ft
Velocity
2.34
ft/s
Velocity Head
0.09
ft
Specific Energy
301.04
ft
Froude Number
1.42
Flow is supercritical.
09/08/12 RowMaster v5.12
11:23:08 AM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1
Cross Section
Cross Section for Irregular Channel
Project Description
Project File
h:\ei6lrv-4\tpfrn7-2\p506ga-u\atfgn9-b\street.fm2
Worksheet
1/2 STREET SECTION -INLET 1-EXISTING
Flow Element
Irregular Channel
Method
Manning's Formula
Solve For
Water Elevation
Section Data
Wtd. Mannings Coefficient 0.013
Channel Slope 0.012000 ft/ft
Water Surface Elevation 300.95 ft
Discharge 1.16 cfs
301.4
301.3
301.2
c
301.1
m
N
W
301.0
300.9
300.8
300.7
-15.0
-1 0.0 -5.0 0.0 5.0 10.0
Station (ft)
09/08/12
11:22:23 AM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666
FlowMaster v5.12
Page 1 of 1
Gutter Flow - Inlet 2 - 25 yr
Worksheet for Irregular Channel
Project Description
Project File
h:\ei61rv-4\tpfrn7-2\p506ga-u\atfgn9-b\street.fm2
Worksheet
1/2 STREET SECTION -INLET 2-EXISTING
Flow Element
Irregular Channel
Method
Manning's Formula
Solve For
Water Elevation
Input Data
Channel Slope
0.016000 ft/ft
Elevation range:
300.73 ft to 301.51 ft.
Station (ft)
Elevation (ft) Start Station
-11.50
301.50 -11.50
0.00
301.23
1.00
301.23
1.00
300.73
2.00
300.82
25.00
301.51
Discharge
9.91 cfs
Results
Wtd. Mannings Coefficient
0.013
Water Surface Elevation
301.15
ft
Flow Area
2.18
ft'
Wetted Perimeter
12.41
ft
Top Width
11.98
ft
Height
0.42
ft
Critical Depth
301.26
ft
Critical Slope
0.004300 ft/ft
Velocity
4.54
ft/s
Velocity Head
0.32
ft
Specific Energy
301.47
ft
Froude Number
1.87
Flow is supercritical.
End Station Roughness
25.00 0,013
09/08/12 FlowMaster v5.12
11:26:38 AM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1
Inlet 2
Cross Section for Irregular Channel
Project Description
Project File
h:\ei6lrv-4\tpfrn7-2\p506ga-u\atfgn9-b\street.fm2
Worksheet
1/2 STREET SECTION -INLET 2-EXISTING
Flow Element
Irregular Channel
Method
Manning's Formula
Solve For
Water Elevation
Section Data
Wtd. Mannings Coefficient 0.013
Channel Slope 0.016000 ft/ft
Water Surface Elevation 301.15 ft
Discharge 9.91 cfs
301
301
301
301
c
0
Y
as 301
W
301
300
300
300..
-15.0
-10.0 -5.0 0.0 5.0 10.0 15.0 20.0
Station (ft)
25.0
09/08/12 FlowMaster v5.12
11:26:16 AM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1
Gutter Flow - Inlet 1 R - 25 yr
Worksheet for Irregular Channel
Project Description
Project File
h:\ei61rv-4\tpfrn7-2\p506ga-u\atfgn9-b\street.fm2
Worksheet
1/2 STREET SECTION -INLET 1R-PROPOSED
Flow Element
Irregular Channel
Method
Manning's Formula
Solve For
Water Elevation
Input Data
Channel Slope 0.013000 ftift
Elevation range: 300.73 ft to 301.50 ft.
Station (ft) Elevation (ft) Start Station End Station Roughness
-11.50 301.50 -11.50 12.50 0.013
0.00 301.23
1.00 301.23
1.00 300.73
2.00 300.82
12.50 301.14
Discharge 2.84 cfs
Results
Wtd. Mannings Coefficient
0.013
Water Surface Elevation
301.02
ft
Flow Area
0.92
ft'
Wetted Perimeter
7.93
ft
Top Width
7.63
ft
Height
0.29
ft
Critical Depth
301.07
ft
Critical Slope
0.004942 ft/ft
Velocity
3.09
ft/s
Velocity Head
0.15
ft
Specific Energy
301.17
ft
Froude Number
1.57
Flow is supercritical.
09/08/12 FlowMaster v5.12
11:24:28 AM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1
Inlet 1 R
Cross Section for Irregular Channel
Project Description
Project File
h:\ei6lrv-4\tpfrn7-2\p506ga-u\atfgn9-b\street.fm2
Worksheet
1/2 STREET SECTION -INLET 1 R-PROPOSED
Flow Element
Irregular Channel
Method
Manning's Formula
Solve For
Water Elevation
Section Data
Wtd. Mannings Coefficient
0.013
Channel Slope
0.013000 ft/ft
Water Surface Elevation
301.02 ft
Discharge
2.84 cfs
301.4
301.3
301.2
x
c
0 301.1
m
0
W
301.0
300.9
300.8
300.7
-15.0
-10.0 -5.0 0.0 5.0 10.0
Station (ft)
15.0
09/08/12
11:24:15 AM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666
FlowMaster v5.12
Page 1 of 1
Gutter Flow - Inlet 2R - 25 yr
Worksheet for Irregular Channel
Project Description
Project File
h:\ei6lrv-4\tpfrn7-2\p506ga-u\atfgn9-b\street.fm2
Worksheet
1/2 STREET SECTION -INLET 2R-PROPOSED
Flow Element
Irregular Channel
Method
Manning's Formula
Solve For
Water Elevation
Input Data
Channel Slope 0.016000 ft/ft
Elevation range: 300.73 ft to 301.51 ft.
Station (ft) Elevation (ft) Start Station End Station Roughness
-11.50 301.50 -11.50 25.00 0.013
0.00 301.23
1.00 301.23
1.00 300.73
2.00 300.82
25.00 301.51
Discharge 9.91 cfs
Results
Wtd. Mannings Coefficient
0.013
Water Surface Elevation
301.15
ft
Flow Area
2.18
ft'
Wetted Perimeter
12.41
ft
Top Width
11.98
ft
Height
0.42
ft
Critical Depth
301.26
ft
Critical Slope
0.004300 ft/ft
Velocity
4.54
ft/s
Velocity Head
0.32
ft
Specific Energy
301.47
ft
Froude Number
1.87
Flow is supercritical.
09/08/12 FlowMaster v5.12
11:27:40 AM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1
Inlet 2R
Cross Section for Irregular Channel
Project Description
Project File
h:\ei6lrv-4\tpfrn7-2\p506ga—u\atfgn9—b\street.fm2
Worksheet
1/2 STREET SECTION -INLET 2R-PROPOSED
Flow Element
Irregular Channel
Method
Manning's Formula
Solve For
Water Elevation
Section Data
Wtd. Mannings Coefficient 0.013
Channel Slope 0.016000 ft/ft
Water Surface Elevation 301.15 ft
Discharge 9.91 cfs
301.5
301.4
301.3
$ 301.2
C
0
as 301.1
W
301.0
300.9
300.8
300.7
-15.0
-10.0 -5.0 0.0 5.0 10.0 15.0 20.0
Station (ft)
25.0
09/08/12 FlowMaster v5.12
11:27.21 AM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1
INLET CALCULATIONS
Existing Storm Sewer Inlet Sta 0+20 (Inlet 1)
Gutter Flow: (cfs)
Q10 1.02
Q25 1.16
Q100 1.37
Inlet on Grade
10 yr
Eo:
0.69
Se:
0.14
Lx:
7.02
Carryover Flow:
10 yr Qco:
0.11
25 yr Qco:
0.12
100 yr Qco:
0.15
Depth
Spread
(ft)
(ft)
0.21
5.6
0.22
5.9
0.23
6.31
Gutter Depression:
0.33
25 yr
100 yr
Eo:
0.67
Eo:
Se:
0.14
Se:
Lx:
7.55
Lx:
Intercepted Flow:
0.91
cfs
1.04
cfs
1.23
cfs
Width of Depressed Gutter:
0.64
0.13
8.28 Li=5 ft
AREA:
0.124
ac Q=CiA
C Factor
0.95
i10
8.63
in/hr Q10 1.02 cfs
i25
9.86
in/hr Q25 1.16 cfs
100
11.64
in/hr Q100 1.37 cfs
Existing Storm Sewer Inlet Sta 2+18 (Inlet 2)
Gutter Flow
Q10
Q25
Q100
Inlet on Grade:
10 yr
Eo:
Se:
Lx:
Carryover Flow:
10 yr Qco:
25 yr Qco:
100 yr Qco:
(cfs)
8.67
9.91
11.69
0.40
0.10
23.68
5.66
6.69
8.20
Depth Spread
(ft)
(ft)
0.4
11.39
0.42
11.98
0.44
12.76
Gutter Depression:
0.33
25 yr
100 yr
Eo:
0.39
Eo:
Se:
0.09
Se:
Lx:
25.49
Lx:
Intercepted Flow:
3.01
cfs
3.22
cfs
3.50
cfs
Width of Depressed Gutter:
0.37
0.09
27.93 Li=5 ft
AREA:
1.196
ac Q=CiA
C Factor
0.84
i10
8.63
in/hr Q10 8.67 cfs
i25
9.86
in/hr Q25 9.91 cfs
i100
11.64
in/hr Q100 11.69 cfs
►a
Carry Over Flow Equation
Qco=Q((1-(La/Lr))A1.8
Cave
0.991 8.09
0.205
E
Carry Over Flow Equation
Qco=Q((1-(La/Lr))A1.8
Cave
0.991 0.84
0.205
INLET CALCULATIONS
Proposed Storm Sewer Inlet Sta 0+20 (inlet 1R)
Gutter Flow: (cfs)
Q10
2.48
Q25
2.84
Q100
3.35
Inlet on Grade:
10 yr
Eo:
0.58
Se:
0.13
Lx:
11.19
Carryover Flow:
10 yr Qco:
0.04
25 yr Qco:
0.12
100 yr Qco:
0.26
Depth
Spread
(ft)
(ft)
0.28
7.24
0.29
7.63
0.31
8.14
Gutter Depression:
0.33
25 yr
100 yr
Eo:
0.56
Eo:
Se:
0.12
Se:
Lx:
12.05
Lx:
Intercepted Flow:
2.44
cfs
2.72
cfs
3.09
cfs
Width of Depressed Gutter:
0.53
0.12
13.21 Li=10 ft
AREA:
0.303
ac Q=CiA
C Factor
0.95
i10
8.63
in/hr Q10 2.48 cfs
i25
9.86
in/hr Q25 2.84 cfs
i100
11.64
in/hr Q100 3.35 cfs
Proposed Storm Sewer Inlet Sta 2+32 (Inlet 2R)
Gutter Flow: (cfs)
Q10
8.67
Q25
9.91
Q100
11.69
Inlet on Grade:
10 yr
Eo:
0.40
Se:
0.10
Lx:
23.68
Carryover Flow:
10 yr Qco:
5.66
25 yr Qco:
6.69
100 yr Qco:
8.20
Depth Spread
(ft)
(ft)
0.4
11.39
0.42
11.98
0.44
12.76
Gutter Depression:
0.33
25 yr
100 yr
Eo:
0.39
Eo:
Se:
0.09
Se:
Lx:
25.49
Lx:
Intercepted Flow:
3.01
cfs
3.22
cfs
3.50
cfs
Width of Depressed Gutter:
0.37
0.09
27.93 Li=5 ft
AREA:
1.196
ac Q=CiA
C Factor
0.84
i10
8.63
in/hr Q10 8.67 cfs
i25
9.86
in/hr Q25 9.91 cfs
i100
11.64
in/hr Q100 11.69 cfs
2
Carry Over Flow Equation
Qco=Q((1-(La/Lr))A1.8
V:
Carry Over Flow Equation
Qco=Q((1-(La/Lr))A1.8
Cave
0.991 0.84
0.205
18" RCP
Worksheet for Circular Channel
Project Description
Project File
h:\ei6lrv-4\tpfrn7-2\p506ga-u\atfgn9-b\street.fm2
Worksheet
18" Storm
Flow Element
Circular Channel
Method
Manning's Formula
Solve For
Full Flow Capacity
Input Data
Mannings Coefficient 0.013
Channel Slope 0,070000 ft/ft
Diameter 18.00 in
Results
Depth
1.50
ft
Discharge
27.79
cfs
Flow Area
1.77
ft2
Wetted Perimeter
4.71
ft
Top Width
0.00
ft
Critical Depth
1.49
ft
Percent Full
100.00
Critical Slope
0.065645 ft/ft
Velocity
15.73
ft/s
Velocity Head
3.84
ft
Specific Energy
FULL
ft
Froude Number
FULL
Maximum Discharge
29.89
cfs
Full Flow Capacity
27.79
cfs
Full Flow Slope
0,070000 ft/ft
09/08/12 FlowMaster v5.12
11:18:43 AM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1