HomeMy WebLinkAboutDrainage ReportDrainage Report
for
Williams Creek Subdivision -Phase 5
College Station, Texas
July, 2006
Revised August, 2006
Developer:
Joe and Janet Johnson Land and Investments, LP
1400 South Commercial Street
Coleman, Texas 76834
(325) 625-2124
Prepared By:
Civil Development, Ltd.
2900 Longmire Drive, Suite K
College Station, Texas 77845
. (979) 764-7743
Prepared for Texco11 General Conrracturs
CERTIFICATION
I certify that this revised report for the drainage design for the Williams Creek Subdivision -
Phase 5, was prepared by me in accordance with the provisions of the City of College Station
Drainage Policy and Design Standards for the owners hereof, with the exception that stom1
water runoff detention is not being proposed for this project since the runoff wi ll discharge
directly into tributaries of Carters Creek and then into the I 00-year floodplain and th e primary
channel of Carters Creek.
TABLE OF CONTENTS
DRAINAGE REPORT-Revised 812006
WILLIAMS CREEK SUBDIVISION -PHASE 5
CERTIFICATION ................................................................................................................................................................. I
TABLE OF CONTENTS ....................................................................................................................................................... 2
LIST OFT ABLES .................................................................................................................................................................. 2
INTRODUCTION .................................................................................................................................................................. 3
GENERAL LOCATION AND DESCRIPTION ................................................................................................................. 3
FLOOD HAZARD INFORMATION ................................................................................................................................... 3
DEVELOPMENT DRAINAGE PATTERNS ...................................................................................................................... 3
DRAINAGE DESIGN CRITERIA ....................................................................................................................................... 3
STORM WATER RUNOFF DETERMINATION .............................................................................................................. 4
STORM CUL VERT & DRAINAGE CHANNEL DESIGN ............................................................................................... 5
CONCLUSIONS ..................................................................................................................................................................... 7
APPENDIX A ......................................................................................................................................................................... 8
Time of Concentration Equations & Calculations
APPENDIX B ........................................................................................................................................................................ 11
Storm Sewer Culvert Data & Design Calculations
APPENDIX C ....................................................................................................................................................................... 14
Drainage Channel Design Data & Calculations
APPENDIX D ....................................................................................................................................................................... 19
Drainage Ditch Data & Lining Material
EXHIBIT A ........................................................................................................................................................................... 22
Drainage Area Map -Post-Development, Culverts & Channels \
EXHIBIT B ........................................................................................................................................................................... 24
Drainage Area Map -Post-Development, Ditch Velocities
LIST OFT ABLES
TABLE 1 -Rainfall Intensity Calculations .............................................................................................. 4
TABLE 2 -Time of Concentration (tc) Equations .................................................................................. 4
TABLE 3 -Post-Development Runoff In formation -Revised 812006 ................................................... 5
TABLE 4 -Area Inlet Eq uati ons & Data -Revised 812006 .................................................................... 6
2
INTRODUCTION
DRAINAGE REPORT-Revised 812006
WILLIAMS CREEK SUBDIVISION -PHASE 5
The purpose of this revised report is to provide the hydrological effects of the construction of
the Williams Creek Subdivision -Phase 5, and to verify that the proposed storm drainage
system meets the requirements set forth by the City of College Station Drainage Policy and
Design Standards.
GENERAL LOCATION AND DESCRIPTION
The project is located on a portion of a 116 acre tract located east of Rock Prairie Road and
south of Greens Prairie Road in College Station, Texas. This report addresses Phase 5 of this
subdivision, which is made up of 30.8 acres. The site is predominantly wooded. The existing
ground elevations range from Elevation 206 to Elevation 250. The general location of the
project site is shown on the vicinity map in Exhibit A.
FLOOD HAZARD INFORMATION
The project site is located in the Carters Creek Drainage Basin. This phase of the proposed
subdivision is located in a Zone X Area according to the Flood Insurance Rate Map prepared
by the Federal Emergency Management Agency (FEMA) for Brazos County, Texas and
incorporated areas, Community No. 481195 and 480083, Panel No. 205D, Map No.
48041C0205D, effective dated February 9, 2000. The location of the Flood Hazard Area
adjacent to this property is shown on Exhibit A as the 100-year floodplain.
DEVELOPMENT DRAINAGE PATTERNS
Prior to development, the storm water runoff for Phase 5 flows in a westerly or easterly
direction into the Carters Creek floodplain or into existing tributaries which discharge into
Carters Creek.
DRAINAGE DESIGN CRITERIA
The design parameters for the storm drainage analysis are as follows:
\
• The Rational Method is utilized to determine peak stom1 water runoff rates for the stom1
drainage design for culverts, ditches and channels.
• Design Storm Frequency
Storm culvert & channel
Roadside ditches
• Runoff Coefficients
25-and l 00-year storm events
10-and 100-year storm events
Post-development (1 acre minimum lot size) c = 0.50
• Rainfall Intensity equations and values for Brazos County can be found in Table 1.
• Time of Concentration, tc -Calculations are based on the method found in the TR-55
publication. Refer to Table 2 for the equations and Appendix A for calculations. The
runoff flow path used for calculating the post-develop ment times of concentration fo r the
larger drainage areas are shown on the ex hibits. Smaller drainage areas use a minimum tc
of 10 minutes to detem1 ine the rainfall intensity values. Exhibit A has the runoff flow paths
used for the drainage areas for the culvert and channel design.
STORM WATER RUNOFF DETERMINATION
The peak runoff values were determined in accordance with the criteria presented in the
previous section for th e 10, 25, 50, and 100-year storm events. The drainage areas for the post-
development condition are shown on Exhibits A & B. Post-development runoff conditions for
the drainage structure design drainage areas are summarized in Table 3.
TABLE 1 -Rainfall Intensity Calculations
Rainfall Intensity Values (in/hr)
Storm
Event
110
'2s
1100
te =
10 min
8.635
9.861
11 .639
I = b I (tc+d)"
I = Rainfall Intensity (in/hr)
tc = U(V*60)
t.: = Time of concentration (min)
L = Length (ft)
V =Velocity (ft/sec)
Brazos County:
10 }'_ear storm 25 }'_ear storm 50 }'_ear storm 100 }'_ear storm
b= 80 b= 89 b= 98 b= 96
d = 8.5 d= 8.5 d = 8.5 d= 8.0
e= 0.763 e= 0.754 e = 0.745 e= 0.730
(Data taken from State Department of Highwa}'_s and Public Transportation Hl'_draulic Manual, page 2-16)
TABLE 2 -Time of Concentration (tc) Equations
The time of concentration was determined using methods found in TR-55, "Urban
Hydrology for Small Watersheds. " The equations are as follows:
Time of Concentration:
For Sheet Flow:
Tc= Tr(shcct now)+ Tt(concentrated sheet now)
where: Tr = Travel Time, minutes
0.007 (n L)0·8
(P z) o.s s o.4 where: T1 = travel time, hours
n =Manning's roughness coefficient
L = flow length, feet
P2 = 2-year, 24-hour rainfall = 4.5"
s = land slope, ft/ft
For Shallow Concentrated Flow: T1 =L I (60*V)
Refer to Appendix A for calcul ations .
..j
where: T1 =travel time, minutes
V =Velocity , fps (See Fig 3-1, App. A)
L = flow length , feet
\
TABLE 3 -Post-Development Runoff Information -Revised 812006
Area 10-year storm
Culvert/ c tc
Channel No. Area # A 110 0 10
(acres) (min) (in/hr) (cfs)
Culvert 4 1 32.20 0.50 26.6 5.297 85.28 -· ---~ --- -Channel 8 2 2.64 0.50 10.0 8.635 11.40 - --------·----Headwal~ Op~_ning -Left 403, 5 2.31 0.50 10.0 8.635 9.97 ----Headwall Opening -Right 404, 6 2.02 0.50 10.0 8.635 8.72
The Rational Method:
Q =CIA I = b I (tc+d)e
Q = Flow (cfs)
A= Area (acres)
tc = Time of concentration (min)
tc = L/(V*60)
L = Length (ft
C = Runoff Coeff.
I = Rainfall Intensity (in/hr)
Brazos County:
10 year storm
b = 80
d = 8.5
e = 0.763
25 year storm
b = 89
d = 8.5
e = 0.754
V =Velocity (ft/sec)
100 year storm
b = 96
d = 8.0
e = 0.730
STORM CULVERT & DRAINAGE CHANNEL DESIGN
25-year storm 100-year storm
l2s 0 2s 1100 0 100
(in/hr) (cfs) (in/hr) (cfs)
6.085 97 .96 7.223 116.30 ---
9.861 13.02 11 .639 15.36 . --
9.861 11 .39 11 .639 13.44 --9.861 9.96 11 .639 11 .76
The culvert for this project has been selected to be Reinforced Concrete Pipe (RCP) meet ing
the requirements of ASTM C-76, Class III pipe meeting the requirements of ASTM C-789.
There wi ll be dissipator blocks at the downstream end of the culvert to slow the discharge out
of the pipe and to help control erosion.
Runoff from the proposed streets will be collected by the roadside ditches and conveyed to the
culvert structures, Drainage Channel No. 8, or to the Rock Prairie Road ditches. Headwall
openings will be used for this development at Culvert No. 4. Th ese openings in the headwalls
will allow the ditches to be less deep at the culvert location, thereby reducing the amoun~ of
disturbance due to the construction of the street ditch side slopes. Th e drainage areas for the
culvert and channel designs are shown on Exhibit A, which also shows the drain age areas
for the headwall openings.
The headwall openings for the left and right side ditches will be placed at the low poi11t of th e
ditch to collect the storm water, which will then be discharged directly through the concrete
headwall and onto the concrete splash pads at each end of the culvert.
The proposed headwall openings were analyzed using the orifice equation, solving for th e
depth of water at the opening for the I 0-and I 00-year storm events. It was assumed that
25% oft/re open area would be clogged for the opening design. Design calculations and data
for tir e headwall openings are shown in Table 4.
TABLE 4 -Area Inlet Equations & Data -Revised 812006
Q = 4.82 * ~ * y 112 ¢ y =(QI (4.82 * ~))2
Where: Q = flow at inlet, cfs
Ag = open area of 1-3'x3' grate, ft2 = 7 .8 ft2
y = depth at inlet, ft
Headwall Actual Design Ag 10-Year Storm
Opening Opening Ag 25%
Location Size clogging 0 10 Depth, y
(ft2) (ft2) (cfs) (ft)
100-Year Storm
0100 Depth, y
(in) (cfs) (ft) (in)
Left 7 -9"x9" 3.94 2.96 9.97 0.49 5.9 13.44 0.89 10.7 ---
Right 7 -9"x9" 3.94 2.96 8.72 0.37 4.5 11 .76 0.68
As shown by these calculations, the maximum depth of water for the I 00-year storm for the
proposed headwall openings is I 0. 7" on the left side. The top of the headwall is Elevation
230.00, and the bottom of the headwall opening is Elevation 228.55. For the JOO-year storm
event, this results in 0.56' of freeboard for Headwall Opening Left, and 0. 77' of freeboard
for Headwall Opening Right. The typical roadway ditch will be constructed such that the ditch
between the right-of-way and the edge of pavement is a minimum of 18" in depth, and will be
graded as necessary to ensure that the runoff from the 100-year storm event will remain within
the street right-of-way.
Appendix 8 presents a summary of the storm culvert design parameters and calculations. The
proposed pipe is 42" in diameter, and it was designed based on the 25-year storm event, and
data is also given for the 100-year storm event. As shown in the summary, the culvert has a
headwater elevation that is at least one foot below the roadway elevation for the 25-year storm
event. Also, the culvert passes the 100-year stom1 event without overtopping the roadway. As
required by College Station, the velocity of flow in the pipes is not lower than 2.5 feet per
second, and it does not exceed 15 feet per second. As the data shows, even during low flow
conditions, the velocity in the pipe wi ll exceed 2.5 feet per second and prevent sediment huild-
up in the culvert. The maximum velocity for the culvert in this development will be 12. l f~et
per second. Appendix 8 contains a summary of the culvert calculator data for the 25-and l 00-
year stom1 events. The culvert will discharge onto a concrete pad with dissipator blocks to
reduce the velocity.
The storm water runoff in the roadside ditches of Williams Ridge Court will discharge into an
improved drainage channel which wi ll convey the water from the street right-of-way to an
existing drainage which ultimately flows into Carters Creek. The channel (Channel No. 8) will
be lined with concrete in the bottom to control possible erosion from the high velocities. The
velocity in the concrete lined channel is 7.8 fps for the 25-year stom1 event and 8.2 fps for the
100-year stonn event at the discharge of th e chann el. Appendix C contains a summary of the
channel design parameters and calculations for the 25-and I 00-year storm events. There will
be dissipator blocks and rock riprap at the end of the channel to slow th e velocity and reduce
erosion .
The velocity of the now in th e roadside ditches was evalu ated for th e I 0-year and I 00-year
storm events. The drai nage areas are shown on Ex hibit B.
8.2
The city requirements for ditch lining material are as follows :
Maximum Design Velocities of Various
Surface Treatments1
Surface Treatment
Exposed Earth*
Grass -Seeded
Grass -Sodded
Impermeable
(Concrete, Gunite, Etc.)
*Temporary Channels Only
Maximum Design Velocity, (ft/sec)
3.0
4.5
6.0
10.0
1From "Erosion and Sediment Control Guidelines for Developing
Areas in Texas" by the Soil Conservation Service
In Appendix D the ditch velocities are summarized including comments stating the ditch lining
material used. The ditch lining material is also shown in the construction drawings. Although
concrete or grass block sod are not required, these have been included in areas where erosion is
anticipated.
CONCLUSIONS
The construction of this project will increase the storm water runoff from this site. However,
the runoff will be carried through a drainage system to existing drainages and then into the 100-
year floodplain. Due to the location of this project and its proximity to Carters Creek's
confluence with the Navasota River, the peak runoff from this development will occur much
sooner than the peak runoff in Carters Creek, therefore, the increase in runoff has no affect on
the water surface elevation in Carters Creek. The increased flow directly into Carters Creek
will not have a significant impact on the surrounding property. No flood damage to
downstream or adjacent landowners is expected as a result of this development.
7
APPENDIX A
Time of Concentration Equations & Calculations
\
Time of Concentration Calculations
Williams Creek Subdivision -Phase 5
Drainage Area #1
Sheet Flow: n= 0.24 {dense grass)
P= 4.5
L= 175 Elev1= Elev2= Slope= 0.018
T1= 0.007(L*n)08 = 0.327 hours= 19.6 min
(P)°-s*(S)o4
Concentrated Flow 1: V= 2.15 fps (unpaved)
L= 357 Elev1= Elev2= Slope= 0.018
T1= L/(60*V) = 2.8 min
Concentrated Flow 2: V= 3.25 fps (unpaved)
L= 760 Elev1= Elev2= Slope= 0.041
T1= L/(60*V) = 3.9 min
Concentrated Flow 3: V= 4.4 fps
L= 75 Elev1= Elev2= Slope= 0.075
T1= L/(60*V) = 0.3 min
\
ITc= 26.6 min
... <+--....
<+-
CV a.
0
VI
CV
VI s...
::I
0 u s...
OJ ..... ..,
3:
3-2
.50
.20 -
.10
.06
.04
. 02 -
.01 -
.005
I
1
j
j
I
' 7
I
' I J
I j .
b
::..q, L'"" ~I
'?1 ::..1 ~ Q_~ ~ J
7 j
I
' I
2
'
I
4
I
I
I
I
I
I
I
6
'
I
J
' I
Average velocity, ft/sec
,. ,
I
' I
I
I r
~
I I
10
7
7
Fiicu,..., :1-L-Av~rai::~ vdociti~· for C•timatinic tmvd tim~ for •hallow conc~ntrat~d no w.
(2 10-Vl -TR-55. Second Ed .. June 198G)
I
20
\
APPENDIXB
Storm Sewer Culvert Data & Design Calculations
\
11
Williams Creek Subdivision -Phase 5
Culvert Summary
Size Length Slope Inlet Invert Culvert #of Elev No. Barrels
(in) (ft) (%) (ft)
4 1 42 80.0 1.00 222.70
Outlet
Invert Elev
(ft)
221.90
Top of Road 25-year storm 100-year storm
Design Flow V2s HW Design Flow V100 HW
(ft) (cfs) (fps) (ft) (cfs) (fps) (ft)
234.60 97.96 10.2 229.15 116.30 12.1 230.84
\
Culv ert 4 -25 Year St orm
Culvert Calcula t or
Enter ed Data:
Shape .......................... .
Number of Barr els .............. .
Solving for .................... .
Chart Number ................... .
Scale Number ................... .
Chart Description .............. .
Scale Descri ption .............. .
Overtopping .................... .
Flowr ate ....................... .
Manning's n .................... .
Roadway Elevation .............. .
Inlet Elevation ................ .
Outlet Elevation ............... .
Diameter ....................... .
Length ......................... .
Entrance Loss .................. .
Tailwater ...................... .
Computed Results:
Headwater ...................... .
Slope .......................... .
Velocity ....................... .
Ci rcular
1
Headwater
1
1
CONCRETE PIPE CULVERT; NO BEVELED RING ENTRANCE
SQUARE EDGE ENTRANCE WITH HEADWALL
Off
97 .96 00 cfs
0 .0140
234.6000 ft
222.7000 ft
221.9000 ft
42.0000 in
80.0000 ft
0 .0000
3.5000 ft
22 9.1535 ft Inlet Control
0.0100 ft/ft
10 .1818 fps
Culvert 4 -100 Year Storm
Culvert Calculator
Entered Data:
Shape .......................... .
Number of Barrels .............. .
Solving for .................... .
Chart Number ................... .
Scale Number ................... .
Chart Description .............. .
Scale Description .............. .
Overtopping .................... .
Flowrate ....................... .
Manning' s n .................... .
Roadway Elevation .............. .
Inlet Elevation ................ .
Outlet Elevation ............... .
Diameter ....................... .
Length ......................... .
Entrance Loss .................. .
Tailwater ...................... .
Computed Results :
Headwater ...................... .
Slope .......................... .
Ve l ocity ....................... .
Williams Creek Su bdivis ion -Phas e 5
College Station , Texas
Ci rcular
1
Headwater
1
1
CONCRETE PIPE CULVERT; NO BEVELED RING EMfRANCE
SQUARE EDGE ENTRANCE WITH HEADWALL
Off
116.3000 cfs
0 .0140
234.6000 ft
222 .7000 ft
221 .9000 ft
42.0000 in
80 .0000 ft
0.0000
3.5000 ft
230 .8430 ft Inlet Control
0.0100 ft /ft
12.0880 fps
APPENDIX C
Drainage Channel Design Data & Calculations
14
Williams Creek Subdivision -Phase 5
Channel Summary
Bottom Side Slope
25-year storm
Channel No. Width Slopes Design Flow Depth
(in) (H:V) (%) (cfs) (in)
8-Segment 1 24 2:1 5.11 13.02 5.0 --8-Segment 2 24 2:1 3.00 13.02 5.8 ------
8-Segment 3 24 2:1 2.00 13.02 6.5
100-year storm Channel
V2s Design Flow Depth V100 Lining
(fps) (cfs) (in) (fps) Material
10.9 15.36 5.5 11.5 Concrete
9.0 15.36 6.4 9.5 Concrete -
7.8 15.36 7.1 8.2 Concrete
\
Channel 8 -25 Year Storm (Segment 1, 5.11% Slope)
Channel Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Height ......................... .
Bottom width ................... .
Left slope ..................... .
Right slope .................... .
Computed Results:
Depth .......................... .
Velocity ....................... .
Full Flowrate .................. .
Flow area ...................... .
Flow perimeter ................. .
Hydraulic radius ............... .
Top width ...................... .
Area ........................... .
Perimeter ...................... .
Percent full ................... .
Trapezoidal
Depth of Flow
13. 0200 cfs
0.0511 ft/ft
0. 0140
15.0000 in
24.0000 in
0. 5000 ft/ft (V/H)
0.5000 ft/ft (V/H)
5.0357 in
10 .9275 fps
110.5277 cfs
1.1915 ft2
46.5205 in
3.6882 in
44 .1429 in
5.6250 ft2
91.0820 in
33.5716 %
Channel 8 -100 Year Storm (Segment 1, 5.11% Slope)
Channel Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Height ......................... .
Bottom width ................... .
Left slope ..................... .
Right slope .................... .
Computed Results:
Depth .......................... .
Velocity ....................... .
Full Flowrate .................. .
Flow area ...................... .
Flow perimeter ................. .
Hydraulic radius ............... .
Top width ...................... .
Area ........................... .
Perimeter ...................... .
Percent full ................... .
Williams Creek Subdivi sion -Phase 5
College Station , Texas
Trapezoidal ·
Depth of 'Flow
15.3600 cfs
0.0511 ft/ft
0. 0140
15.0000 in
24.0000 in
0.5000 ft/ft (V/H)
0.5000 ft/ft (V/H)
5.5077 in
11. 4690 fps
110 .5277 cfs
1.3393 ft2
48.6312 in
3.9657 in
46.0308 in
5.6250 ft2
91.0820 in
36.7180 %
\
Channel 8 -25 Year Storm (Segment 2, 3.0% Slope)
Channel Calculator
Given Input Data :
Shape .......................... .
Solving for .................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Height ......................... .
Bottom width ................... .
Left slope ..................... .
Right slope .................... .
Computed Results:
Depth .......................... .
Velocity ....................... .
Full Flowrate .................. .
Flow area ...................... .
Flow perimeter ................. .
Hydraulic radius ............... .
Top width ...................... .
Area ........................... .
Perimeter ...................... .
Percent full ................... .
Trapezoidal
Depth of Flow
13 .0200 cfs
0.0300 ft/ft
0.0140
15 .0000 in
24 .0000 in
0.5000 ft/ft (V/H)
0. 5000 ft/ft (V/H)
5.8153 in
9.0485 fps
84.6879 cfs
1.4389 ft2
50.0069 in
4.1435 in
47.2613 in
5 .6250 ft2
91.0820 in
38.7688 %
Channel 8 -100 Year Storm (Segment 2, 3.0% Slope)
Channel Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Height ......................... .
Bottom width ................... .
Left slope ..................... .
Right slope .................... .
Computed Results:
Depth .......................... .
Velocity ....................... .
Full Flowrate .................. .
Flow area ...................... .
Flow perimeter ................. .
Hydraulic radius ............... .
Top width ...................... .
Area ........................... .
Perimeter ...................... .
Percent full ................... .
Williams Creek Subdivision -Phase 5
College Statio n, Texas
Trapezoidal ,
Depth of Flow
15.3600 cfs
0.0300 ft/ft
0 . 0140
15.0000 in
24.0000 in
0.5000 ft/ft (V/H)
0.5000 ft/ft (V/H)
6 .3518 in
9 .4874 fps
84.6879 cfs
1 .6190 ft2
52.4062 in
4.4486 in
49 .4073 in
5.6250 ft2
91.0820 in
42 .3454 %
\
Channel 8 -25 Year Storm (Segment 3, 2.0% Slope)
Channel Calculator
Given Input Data :
Shape .......................... .
Solving for .................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Height ......................... .
Bottom width ................... .
Left slope ..................... .
Right slope .................... .
Computed Results:
Depth .......................... .
Velocity ....................... .
Full Flowrate .................. .
Flow area ...................... .
Flow perimeter ................. .
Hydraulic radius ............... .
Top width ...................... .
Area ........................... .
Perimeter ...................... .
Percent full ................... .
Trapezoidal
Depth of Flow
13. 0200 cfs
0.0200 ft /ft
0.0140
15.0000 in
24.0000 in
0 .500 0 ft/ft (V/H)
0 . 5000 ft/ft (V/H)
6 .4793 in
7.8294 fps
69.1474 cfs
1.6630 ft2
52.9764 in
4.5203 in
49.9173 in
5 .6250 ft2
91.0820 in
43.1955 %
Channel 8 -100 Year Storm (Segment 3 , 2.0% Slope)
Channel Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Height ......................... .
Bottom width ................... .
Left slope ..................... .
Right slope .................... .
Computed Results:
Depth .......................... .
Velocity ....................... .
Full Flowrate .................. .
Flow area ...................... .
Flow perimeter ................. .
Hydraulic r adius ............... .
Top width ...................... .
Area ........................... .
Perimeter ...................... .
Percent full ................... .
Will iams Creek Subdiv i sion -Phase 5
College Stati on, Texas
Trapezoidal .
Depth of Flow
15.3600 cfs
0.0200 ft/ft
0 .0140
15 .0000 in
24.0000 in
0 .5000 ft/ft (V/H)
0.5000 ft/ft (V/H)
7.0695 in
8 .2034 fps
69 .1474 cfs
1.8724 ft2
55 .6159 in
4.8480 in
52 .2781 in
5.6250 ft2
91.0820 in
47.1302 %
\
APPENDIXD
Drainage Ditch Data & Lining Material
\
19
Williams Creek Subdivision -Phase 5
Ditch Velocity Data
Revised 812006
Williams Creek Drive
Left Ditch (n = O 035 for grass and n = 0 014 for concrete)
From To Station Slope Drainage Area # 0 10
Station (ds)
54+60 54+80 7.95% 403 5.14
54+80 55+26 0.40% 403 5.14
55+26 55+60 -0.40% 1,2,3,4 4.62
55+60 55+80 -11 .70% 1,2,3,4 4.62 -55+80 56+37 -3.20% 1,2,3.4 4.62
56+37 57+50 -5.60% 2,3.4 4.27
57+50 58+82 -4.60% 3,4 3.84
58+82 60+86 -1 .75% 4 3.28 -----61+90 64+73 0.90% 21 0.95
Williams Ridge Court
Left Ditch (n = 0.035)
From To Station Slope Drainage Area # 0 10
Station (cfs)
0+00 2+00 2.00% 5 1.17 ---
2+00 3+50 1.00% 5,6 1.73 ---------
3+50 5+25 1.56% 5,6,7 2.37 -----5+25 6+50 1.89% 5,6,7,8 2.81 -----------6+50 8+25 2.15% 5~.7~~-3.41 -·-------8+25 10+25 2.14% 5,6,7,8~9._!~ 4.19 ---10+25 12+00 3.82% 5,6_,I.8.~.10, 11 4.88 ----12+00 13+16.34 5.10% 5,6.7,8,9,10, 11 , 12 5.79
Williams Creek Drive
Right Ditch (n = 0.035 for grass and n = 0.014 for concrete)
From To Station Slope Drainage Area # 0 10
Station (els)
54+60 54+97 4.80% 404 6.09 -----------
54+97 55+26 0.40% 404 609 -----
55+26 55+45 -0.40% 2~.24J~.26 2.50 ----
55+45 55+80 -7.11% 23,24,25,26 2.50 ---55+80 56+37 -3.20% 23,24J5~2_6 2.50 -------------56+37 57+50 -5.60% 23 ,24,25 2.16 ----------57+50 58+82 -4.60% 23,24 1.77 ----58+82 60+86 -1.75% 23 1.25 ----60+86 60+86 -1.75% 22 2.12
Williams Ridge Court
Right Ditch (n = 0.035)
From To Station Slope Drainage Area # 0 10
Station (cfs)
0+00 2+00 2.00% 20 0.82
2+00 3+50 1.00% 19,20 1.42
3+50 5+25 1.56% 18.19,20 2.12
5+25 6+50 1.89% 17,18,19,20 2.63
6+50 8+25 2.15% 16,17,18,19,20 3.32
8+25 10+25 2.14% 15.16.17.18.19.20 4.06
10+25 12+00 3.82% 14. 15.16, 17, 18.1 9.20 4.71
12+00 13+16.34 5.10% h3, 14.15.16, 17.18.19.2( 5.61
1. Concrete ditch lining depth = 9··
2 Concrete ditch lining deplh = 7 5 ..
V 10 d 10 0100 V100 d100 Driveway Lot# Ditch Lining
(fps) (in) (els) (fps) (in) Culvert (in) Material
9.5 4.4 6.93 10.2 4.9 --Concrete 2
3.2 5.9 6.93 3.4 6.9 --Concrete'
3.2 5.9 6.23 3.4 6.9 - -Concrete 1
10.7 3.9 6.23 11.5 4.4 --Concrete2
3.3 7.1 6.23 3.6 7.9 18 1 Grass Sod -
4.0 6.2 5.76 4.3 6.9 18 1 Grass Sod
3.6 6.2 5.18 3.9 6.9 15 2 Grass Seed
2.4 7.0 4.42 2.6 7.8 15 -Grass Seed
1.4 5.0 1.28 1.5 5.6 12 -Grass Seed
V10 d 10 0100 V 100 d100 Driveway Lot# Ditch Lining
(fps) (in) (cfs) (fps) (in) Culvert (in) Material
2.0 4.6 1.57 2.1 5.2 12 11 Grass Seed
1.7 6.1 2.33 1.8 6.8 12 12 Grass Seed --2.1 6.3 3.20 2.3 7.1 12 12 Grass Seed
2.4 6.5 3.78 2.6 7.3 12 13 Grass Seed -2.6 6.8 4.60 2.8 7.6 15 14 Grass Seed ---2.8 7.4 5.65 3.0 8.3 15 14 Grass Seed
3.6 7.0 6.58 3.9 7.8 18 15 Grass Seed --4.2 7.1 7.80 4.5 7.9 18 16 Grass Sod
V10 d 10 0 100 V100 d100 Driveway Lot# Ditch Lining
(fps) (in) (ds) (fps) (in) Culvert (in) Material
8.2 5.2 8.21 8.8 5.8 --Concrete' ---
Concrete 1• 2.7 4.2 8.21 2.9 5.0 - ---Concrete 1 \ 2.7 4.2 3.38 2.9 5.0 --
7.6 3.4 3.38 8.2 3.9 --Concrete 2
---
2.8 5.6 3.38 3.1 6.3 12 1 Grass Sod ------
3.4 4.8 2.91 3.6 5.4 12 1 Grass Sod -3.0 4.6 2.39 3.2 5.2 12 2 Grass Seed --
1.9 4.9 1.69 2.0 5.4 12 2 Grass Seed ---
1.7 6.7 2.85 1.8 7.5 12 3.4 Grass Seed
V10 d 10 0 100 V100 d 100 Driveway Lot # Ditch Lining
(fps) (in) (efs) (fps) (in) Culvert (in) Material
1.8 4.1 1.11 1.9 4.5 12 23.24 Grass Seed
1.6 5.7 1.92 1.7 6.3 12 22 Grass Seed
2.1 6.1 2.85 22 6.8 12 21 Grass Seed
2.4 6.3 3.55 2.5 7.1 12 20 Grass Seed
2.6 6.8 4.48 2.8 7.6 15 19 Grass Seed
2.8 7.3 5.47 3.0 8.2 15 19 Grass Seed
3.5 6.9 6.34 3.8 7.7 18 18 Grass Seed
4.1 7.0 7.57 4.5 7.8 18 17 Grass Sod
Williams Creek Subdivision -Phase 5
Ditch Velocity Evaluation Data -Exhibit B
Revised 812006
Area, c tc 5 year storm
Area # A Is Os
(acres) (min) (in/hr) (cfs)
1 0.08 0.50 10.0 7.693 0.31
2 0.10 0.50 10.0 7.693 0.38
3 0.13 0.50 10.0 7.693 0.50
4 0.76 0.50 10.0 7.693 2.92
5 0.27 0.50 10.0 7.693 1.04
6 0.13 0.50 10.0 7.693 0.50
7 0.15 0.50 10.0 7.693 0.58
8 0.10 0.50 10.0 7.693 0.38
9 0.14 0.50 10.0 7.693 0.54
10 0.18 0.50 10.0 7.693 0.69
11 0.16 0.50 10.0 7.693 0.62
12 0.21 0.50 10.0 7.693 0.81
13 0.21 0.50 10.0 7.693 0.81
14 0.15 0.50 10.0 7.693 0.58
15 0.17 0.50 10.0 7.693 0.65
16 0.16 0.50 10.0 7.693 0.62
17 0.12 0.50 10.0 7.693 0.46
18 0.16 0.50 10.0 7.693 0.62
19 0.14 0.50 10.0 7.693 0.54
20 0.19 0.50 10.0 7.693 0.73
21 0.22 0.50 10.0 7.693 0.85
22 0.49 0.50 10.0 7.693 1.88
23 0.29 0.50 10.C 7.693 1.12
24 0.12 0.50 1C.O 7.693 0.46
25 0.09 0.50 10.0 7.693 0.35
26 0.08 0.50 10.0 7.693 0.31
403 1.19 0.50 10.0 7.693 4.58 ---404 1.41 0.50 10.0 7.693 5.42
The Rational Method:
Q = CIA I = b I (tc+d)e
Q = Flow (cfs) le = Time of concentration (min)
A = Area (acres)
C = Runoff Coeff.
I = Rainfall Intensity (in/hr)
Brazos County:
5 year storm 10 yea r storm
b = 76 b = 80
d = 8.5 d = 8.5
e = 0.79 e = 0.763
25 year storm
b = 89
d = 8.5
e = 0.754
10 year storm 25 year storm 50 year storm
110
(in/hr)
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
8.635
0 10 l2s
(cfs) (in/hr)
0.35 9.861
0.43 9.861
0.56 9.861
3.28 9.861
1.17 9.861
0.56 9.861
0.65 9.861
0.43 9.861
0.60 9.861
0.78 9.861
0.69 9.861
0.91 9.861
0.91 9.861
0.65 9.861
073 9.861
0.69 9.861
0.52 9.861
0.69 9.861
0.60 9.861
0.82 9.861
0.95 9.861
2.12 9.861
1.25 9.861
0.52 9.861
0.39 9.861
0.35 9.861
5.14 9.861
6.09 9.861
tc = L/(V*60)
L = Length (ft
0 2s lso Oso
(cfs) (in/hr) (cfs)
0.39 11 .148 0.45
0.49 11 .148 0.56
0.64 11.148 0.72
3.75 11 .148 4.24
1.33 11 .148 1.50
0.64 11 .148 0.72
0.74 11.148 0.84
0.49 11.148 0.56
0.69 11 .148 0.78
0.89 11.148 1.00
0.79 11.148 0.89
1.04 11.148 1.17
1.04 11.148 1.17
0.74 11.148 0.84
0.84 11 .148 0.95
0.79 11 .148 0.89
0.59 11.148 0.67
0.79 11.148 0.89
0.69 11.148 0.78
0.94 11.148 1.06
1.08 11 .148 1.23
2.42 11 .148 2.73
1.43 11.148 1.62
0.59 11 .148 0.67
0.44 11 .148 0.50
0.39 11 .148 0.45
5.87 11 .148 6.63 -6.95 11.148 7.86
V =Velocity (ft/sec)
50 year storm
b = 98
d = 8.5
e = 0.745
100 year storm
b = 96
d = 8.0
e = 0.730
100 year storm
1100 0 100
(in/hr) (cfs)
11 .639 0.47
11 .639 0.58
11 .639 0.76
11 .639 4.42
11 .639 1.57
11 .639 0.76
11 .639 0.87
11 .639 0.58
11 .639 0.81
11 .639 1.05
11 .639 0.93
11 .639 1.22
11 .639 1.22
11 .639 0.87
11 .639 0.99
11 .639 0.93
11 .639 0.70
11 .639 0.93
11.639 0.8 1
11 .639 1.11
11 .639 1.28
11 .639 2.85
11 .639 1.69
11 .639 0.70
11 .639 0.52
11.639 0.47
11.639 6.93
11 .639 8.21
\
EXHIBIT A
Drainage Area Map -Post-Development, Culverts & Channels
\
22
EXHIBIT B
Drainage Area Map -Post-Development, Ditch Velocities
24