HomeMy WebLinkAboutDrainage ReportDrainage Report
for
Williams Creek Subdivision -Phase 2
College Station, Texas
November 2004
Developer:
Joe and Janet Johnson Land and Investments, LP
1400 South Commercial Street
Coleman, Texas 76834
(325) 625-2124
Prepared By:
TEXCON General Contractors
1707 Graham Road
College Station, Texas 77845
(979) 764-7743
CERTIFICATION
I certify that this report for the drainage design for the Williams Creek Subdivision -Phase 2,
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 stonn water runoff
detention is not being proposed for a portion of this project since the runoff will discharge
directly into an existing drainage which flows into the 100-year floodplain limits.
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TABLE OF CONTENTS
DRAINAGE REPORT
WILLIAMS CREEK SUBDIVISION -PHASE 2
CERTIFICATION .................................................................................................................................................................. 1
TABLE OF CONTENTS ........................................................................................................................................................ 2
LIST OF TABLES .................................................................................................................................................................. 3
INTRODUCTION .................................................................................................................................................................. .4
GENERAL LOCATION AND DESCRIPTION ................................................................................................................. .4
FLOOD HAZARD INFORMATION .................................................................................................................................... 4
DEVELOPMENT DRAINAGE PATTERNS ...................................................................................................................... .4
DRAINAGE DESIGN CRITERIA ....................................................................................................................................... .4
STORM WATER RUNOFF DETERMINATION ............................................................................................................... 5
DETENTION FACILITY DESIGN ...................................................................................................................................... 7
STORM CULVERT & DRAINAGE CHANNEL DESIGN .............................................................................................. 10
CONCLUSIONS ................................................................................................................................................................... 11
APPENDIX A ........................................................................................................................................................................ 12
Time of Concentration Equations & Calculations
APPENDIX B ........................................................................................................................................................................ 26
Storm Sewer Culvert Data & Design Calculations
APPENDIX C ........................................................................................................................................................................ 31
Drainage Channel Design Data & Calculations
APPENDIX D ........................................................................................................................................................................ 34
Drainage Ditch Data & Lining Material
APPENDIX E ........................................................................................................................................................................ 37
Detention Pond Design Information
EXHIBIT A ............................................................................................................................................................................ 44
Drainage Area Map -Pre-Development Detention Pond
EXHIBIT B ............................................................................................................................................................................ 46
Drainage Area Map -Post-Development Detention Pond
EXHIBIT C ............................................................................................................................................................................ 48
Drainage Area Map -Post-Development
EXHIBIT D ............................................................................................................................................................................ 50
Drainage Area Map -Post-Development Ditch Velocities
2
LIST OF TABLES
TABLE 1 -Rainfall Intensity Calculations .............................................................................................. 5
TABLE 2 -Time of Concentration (tc) Equations .................................................................................. 6
TABLE 3A -Post-Development Runoff Information (Exhibit C) .......................................................... 6
TABLE 3B -Drainage Structure Flow Summary .................................................................................... 7
TABLE 4 -Pre-& Post-Development Runoff Information -Detention Evaluation .............................. 7
TABLE 5 -Pre-& Post-Development Peak Discharge Comparison -.................................................... 8
Discharge Point No. 1 with Detention Pond .................................................................... 8
TABLE 6 -Summary of Maximum Pond Water Levels ......................................................................... 8
TABLE 7 -Pre-& Post-Development Peak Discharge Comparison -.................................................... 9
Discharge Point No. 2 with Detention Pond .................................................................... 9
TABLE 8 -Summary of Maximum Pond Water Levels ....................................................................... 10
3
DRAINAGE REPORT
WILLIAMS CREEK SUBDIVISION -PHASE 2
INTRODUCTION
The purpose of this report is to provide the hydrological effects of the construction of the
Williams Creek Subdivision -Phase 2, 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 213.91 acre tract located east of Rock Prairie Road and
south of Greens Prairie Road in College Station, Texas. This report addresses Phase 2 of this
subdivision, which is made up of 56 .69 acres. The site is predominantly wooded. The existing
ground elevations range from Elevation 200 to Elevation 284. Portions of the existing ground
are steep, with slopes approaching 10%. 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. Most of the proposed developed
area of the site 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. A portion of this development is in the 100-
year floodplain. This area is shown on Exhibit A as the 100-year floodplain limit. Lots with
floodplain are required to have a minimum finished floor elevation (FF), which is a minimum
of one foot above the Base Flood Elevation (BFE). The BFE information is also shown on
Exhibit A.
DEVELOPMENT DRAINAGE PATTERNS
Prior to development, the storm water runoff for a portion of Phase 2 flows in a north and
northwesterly direction into Phase 1 of the development or existing tributaries which discharge
into Carters Creek. The runoff from the remainder of the site flows south to Rock Prairie Road
and then to Lick Creek. The pre-development drainage areas for the detention pond design are
shown on Exhibit A.
DRAINAGE DESIGN CRITERIA
The design parameters for the storm drainage analysis are as follows:
• The Rational Method is utilized to detennine peak stonn water runoff rates for the stom1
drainage design for culverts, ditches and channels.
• HEC-l Program -Utilized to determine peak storm water runoff rates for the detention
facility design.
• Design Stonn Frequency
Storm culverts
Detention facility analysis
4
10 and 100-year storm events
5, 10, 25, 50 and 100-year storm events
• Runoff Coefficients
Post-development (1 acre minimum lot size) c = 0.50
• Runoff Curve Number (CN) -Detention Pond
The Brazos County Soil Survey shows the soils in the area to be classified as hydrologic
group D soils. The pre-development CN is based on no development on the site. The
post-development CN is based on development of Phase 2 of the subdivision. The CN
calculations are found in Appendix E.
• 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 pre-and post-development times of concentration
for the larger drainage areas are shown on the exhibits. Smaller drainage areas use a
minimum 1:c of 10 minutes to determine the rainfall intensity values. Exhibit B has the
runoff flow paths used for the drainage areas for the detention pond design. Exhibit C has
the runoff flow paths used for the drainage areas for the culvert design. Exhibit D has the
runoff flow paths used for the drainage areas for the roadside ditch design.
STORM WATER RUNOFF DETERMINATION
The peak runoff values were determined in accordance with the criteria presented in the
previous section for the 10, 25, 50, and 100-year storm events. The drainage areas for the post-
development condition are shown on Exhibit A. Post-development runoff conditions for the
storm culvert design drainage areas are summarized in Tables 3A & 3B. The pre-and post-
development runoff information for the detention pond evaluation is shown in Table 4.
TABLE 1 -Rainfall Intensity Calculations
Rainfall Intensity Values (in/hr)
Storm tc =
Event 10 min
110 8.635
'2s 9.861
lso 11 .148
1100 11 .639
Brazos County:
10 year storm 25 year storm
b = 80 b= 89
d= 8.5 d = 8.5
e= 0.763 e= 0.754
I = b I (tc+d)e
I = Rainfall Intensity (in/hr)
tc = U(V*60)
tc =Time of concentration (min)
L = Length (ft)
V =Velocity (ft/sec)
50 year storm 100 year storm
b = 98 b= 96
d= 8.5 d = 8.0
e= 0.745 e= 0.730
(Data taken from State Department of Highways and Public Transportation Hydraulic Manual, page 2-16)
5
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: Tc= T r(sheet flow)+ Tr(concentrated sheet flow)
where: Tr =Travel Time, minutes
For Sheet Flow: 0.007 (n L)°-8
(Pi) o.s s o.4 where: Tr =travel time, hours
For Shallow Concentrated Flow:
Refer to Appendix A for calculations.
n =Manning's roughness coefficient
L = flow length, feet
P2 = 2-year, 24-hour rainfa ll = 4.5"
s = land slope, ft/ft
T1 =LI (60*V)
where: Tr = travel time, minutes
V =Velocity, fps (See Fig 3-1 , App. E)
L = flow length, feet
TABLE 3A -Post-Development Runoff Information (Exhibit C)
Area 5 year storm 1 O year storm 25 year storm 50 year storm 100 year storm c tc Area# (acres) Is Os
A (min) (in/hr) (cfs)
8 1.16 0.50 10.0 7.693 4.46
18 0.21 0.50 10.0 7.693 0.81
24A 5.29 0.50 27.8 4.532 11.99
25 0.51 0.50 10.0 7.693 1.96
26 1.16 0.50 10.0 7.693 4.46
27 3.85 0.50 22.9 5.078 9.78
34 15.62 0.50 25.0 4.827 37.70
35 1.14 0.50 23.3 5.028 2.87
The Rational Method:
Q = CIA I = b I (tc+d)e
Q = Flow (cfs)
A= Area (acres)
C = Runoff Coeff.
tc = Time of concentration (min)
I = Rainfall Intensity (in/hr)
Brazos County:
5 vear storm 1 O vear 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 = 0.75
110
(in/hr)
8.635
8.635
5.163
8.635
8.635
5.767
5.489
5.711
010 l2s
(cfs) (in/hr)
5.01 9.861
0.91 9.861
13.66 5.932
2.20 9.861
5.01 9.861
11.10 6.618
42.87 6.302
3.26 6.555
tc = L/(V*60)
L = Length (ft
0 2s 150 Oso
(cfs) (in/hr) (cfs)
5.72 11 .148 6.47
1.04 11 .148 1.17
15.69 6.747 17.85
2.51 11 .148 2.84
5.72 11 .148 6.47
12.74 7.516 14.47
49.22 7.163 55.94
3.74 7.446 4.24
V =Velocity (ft/sec)
6
50 year storm
b = 98
d = 8.5
e = 0.745
100 year storm
b = 96
d = 8.0
e = 0.730
1100 0100
(in/hr) (cfs)
11 .639 6.75
11 .639 1.22
7.046 18.64
11 .639 2.97
11 .639 6.75
7.845 15.10
7.477 58.40
7.772 4.43
TABLE 3B -Drainage Structure Flow Summary
tc 5 year storm 1 O year storm 25 year storm 50 year storm 100 year storm
Culvert# Contributing Contributing c Area No. Area Acreage Is Os 110 010 l2s 02s lso Oso 1100
(min) (in/hr) (cfs) (in/hr) (cfs) (in/hr) (cfs) (in/hr) (cfs) (in/hr)
8 25 0.51 0.50 10.0 7.693 1.96 8.635 2.20 9.861 2.51 11.148 2.84 11.639
9 26 1.16 0.50 10.0 7.693 4.46 8.635 5.01 9.861 5.72 11 .148 6.47 11 .639
10 27 3.85 0.50 18.5 5.078 9.78 5.767 11.10 6.618 12.74 7.516 14.47 7.845
Channel#
9 18,27 4.06 0.50 18.5 5.078 10.31 5.762 11.70 6.618 13.43 7.516 15.26 7.845
TABLE 4 -Pre-& Post-Development Runoff Information -Detention Evaluation
Area# Area CN tc Lag
(acres) (min) (hrs)
Pre 101 8.11 73.4 43.9 0.439
Pre 102 17.74 73.2 44.7 0.447
Post 201 8.93 79.2 29.0 0.290
Post 202 10.13 76.8 31.4 0.314
Post 203 0.96 80.1 10.0 0.100
Post 204 5.29 73.6 27.8 0.278
DETENTION FACILITY DESIGN
The runoff from the development of Phase 1 of the Williams Creek Subdivision discharges
directly into tributaries of Carters Creek and then almost immediately into the 100-year
floodplain. The storm water runoff collected by the roadside ditches from the portion of Phase
2 of the subdivision that flows to Carters Creek will be discharged into the roadside ditches of
Williams Creek Drive or into the future development area of the subdivision. The Williams
Creek Drive -Phase 1 roadway ditches were designed for the development of Phase 2. The
runoff from the portion of the subdivision that drains into the future development areas
ultimately will drain to Carters Creek or its tributaries. Therefore, since runoff is discharged
into the floodplain, detention will not be required for the construction of Phase 1 and a portion
of Phase 2 of the subdivision. The runoff from Phase 2 that drains to Rock Prairie Road and
ultimately to Lick Creek must be detained to pre-development flow levels. This will be
achieved by constructing 2 detention ponds with Phase 2. Detention Pond No. 2 is a temporary
pond that will be replaced with the construction of a permanent detention pond in Phase 4.
Detention Pond No. 1
The detention facilities for the runoff from this site will be constructed as shown on Exhibit B.
Detention Pond No. 1 is located on the existing drainage ditch adjacent to Rock Prairie Road.
The outfall of this detention pond discharges into an existing culvert which will be referred to
as Discharge Point No. 1 in this report.
The pond outlet structure is a concrete riser structure which is 4'x 4' in size, 3.0' high, and with
a 3 'x 3' opening at its top. There is a 15" wide opening in the front face of the structure with
its invert at Elevation 267.0 to control the flow. The discharge pipe is a 27" RCP, 18 feet in
length, with a concrete S.E.T. at the discharge end. Concrete riprap will be placed at the
discharge end to control erosion. The pipe has a design slope of 1.0%. The top of the pond
7
0100
(cfs)
2.97
6.75
15.10
15.93
berm is at Elevation 271.0. A 20 feet wide emergency overflow spillway is provided at the
center of the berm. The spillway flow line is Elevation 270.5.
The peak flow out of the detention facility was determined by the HEC-1 program using the
depth discharge data for the pond outlet structure as provided in Appendix E. As shown in
Table 5, the peak outflow from the detention facility is less than the allowable peak outflow for
the design storm event. Additionally, Table 6 presents the maximum water surface in the pond
for each storm event, as well as the amount of freeboard provided.
The data shown in Tables 5 & 6 are from the HEC-1 computer model. The summary printout
of the model is not included in this report. This data can be provided if necessary.
A comparison of the pre-& post-development peak discharge values for Discharge Point No. 1
shows an increase of 21 cfs in the runoff for the 100-year storm event, from 28 cfs to 49 cfs.
Table 5 shows the increases in runoff for the other storm events if there was not a detention
pond to control the runoff Because of this increased runoff, a detention pond is proposed,
which will reduce the peak runoff to less than or equal to the pre-development runoff at
Discharge Point No. 1, as the "Post-Development with Pond" data in Table 5 shows.
TABLE 5 -Pre-& Post-Development Peak Discharge Comparison -
Discharge Point No. 1 with Detention Pond
Location Os 010 0 25
(cfs) (cfs) (cfs)
Pre-Development
Total @ Discharge Pt. No. 1 12 15 20
Post-Development without Pond
Total @ Discharge Pt. No. 1 24 29 37
Post-Development with Pond
Into Pond 22 27 34
Out of Pond 12 14 18
Total@ Discharge Pt. No. 1 12 15 19 (Pond Discharge & Area 203)
TABLE 6-Summary of Maximum Pond Water Levels
Oso
(cfs)
24
43
39
20
22
Storm Event Water Surface Freeboard,
Elevation, ft. ft.
5-year 269.1 1.9
10-year 269.4 1.6
25-year 269.8 1.2
50-year 270.1 0.9
1 OD-year 270.3 0.7
Note: Detention Pond Top of Berm Elevation= 271 .0
0 100
(cfs)
28
49
45
23
24
The area-capacity data and the depth-discharge data for the Detention Pond No. l are provided
in Appendix E. The detention pond grading plan is shown in the construction drawings.
Detention Pond No. 2
Discharge Point No. 2 is where the runoff from a small portion of the Phase 2 development
discharges into a cul vert on Rock Prairie Road . Detention Pond No. 2 is a temporary pond
8
located on the future right-of-way of Williams Creek Drive. With the development of Phase 4
of the subdivision, the pond will be removed and the permanent pond will be constructed
adjacent to Rock Prairie Road.
The pond outlet structure is the discharge pipe. The discharge pipe is a 27" RCP, 16 feet in
length, with a concrete S.E.T. at the discharge end. The upstream invert elevation of the
concrete S.E.T. is 267.0. Rock riprap wi ll be placed at the discharge end to control erosion.
The pipe has a design slope of 1.0%. The top of the pond berm is at Elevation 271 .0. A 20 feet
wide emergency overflow spillway is provided at the center of the berm. The spillway flow line
is Elevation 270.5 .
The peak flow out of the detention facility was determined by the HEC-1 program using the
depth discharge data for the pond outlet structure as provided in Appendix E. As shown in
Table 7, the peak outflow from the detention facility is less than the allowable peak outflow for
the design storm event. Additionally, Table 8 presents the maximum water surface in the pond
for each storm event, as well as the amount of freeboard provided.
The data shown in Tables 7 & 8 are from the HEC-1 computer model. The summary printout
of the model is not included in this report. This data can be provided if necessary.
A comparison of the pre-& post-development peak discharge values for Discharge Point No. 2
shows an increase of 6 cfs in the runoff for the 100-year storm event, from 67 cfs to 61 cfs.
Table 5 shows the increases in runoff for the other storm events if there was not a detention
pond to control the runoff. Because of this increased runoff, a detention pond is proposed,
which will reduce the peak runoff to less than or equal to the pre-development runoff, as the
"Post-Development with Pond" data in Table 8 shows.
TABLE 7 -Pre-& Post-Development Peak Discharge Comparison -
Discharge Point No .• 2 with Detention Pond
Location 05 010 0 25
(cfs) (cfs) (cfs)
Pre-Development
Total @ Discharge Pt. No. 2 26 33 44
Post-Development without Pond
Total @ Discharge Pt. No. 2 31 38 50
Post-Development with Pond
Into Pond 21 26 33
Out of Pond 15 16 19
Total@ Discharge Pt. No. 2 22 27 32 (Pond Discharge & Area 204)
0 50 0100
(cfs) (cfs)
52 61
58 67
39 45
21 23
36 41
The area-capacity data and the depth-discharge data for the Detention Pond No. 2 are provided
in Appendix E. The detention pond grading plan is shown in the construction drawings
9
TABLE 8 -Summary of Maximum Pond Water Levels
Storm Event Water Surface Freeboard,
Elevation, ft. ft.
5-year 269.0 2.0
10-year 269.1 1.9
25-year 269.4 1.6
50-year 269.6 1.4
100-year 269.8 1.2
Note: Detention Pond Top of Berm Elevation= 271 .0
STORM CUL VERT & DRAINAGE CHANNEL DESIGN
The storm culverts for this project have been selected to be Reinforced Concrete Pipe (RCP)
meeting the requirements of ASTM C-76, Class III pipe meeting the requirements of ASTM C-
789. There will be sloped safety end treatment at the end of each culvert.
Runoff from the proposed streets will be collected by the roadside ditches and conveyed to the
culvert structures. Due to the open-ditch design, no inlets will be used for this development.
The drainage areas for the culvert design are shown on Exhibit C.
Appendix B presents a summary of the storm culvert design parameters and calculations. All
pipes are 18" in diameter or larger. The culverts were designed based on the 10-year storm
event, and data is also given for the 100-year storm event. As shown in the summary, all of the
culverts have a headwater elevation that is at least one foot below the roadway elevation for the
10-year storm event. Also, all of the culverts pass the 100-year storm 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 pipes will exceed 2.5 feet per
second and prevent sediment build-up in the culverts. The maximum flow in the storm culverts
will occur in Culvert No. 10. The maximum velocity for the culverts in this development will
be 7 .3 feet per second and will occur in Culvert No. 10. Appendix B contains a summary of
the culvert calculator data for the 10 and 100-year storm events. Concrete riprap will be placed
at the end of the culverts when the velocity exceeds 4.5 fps for the 10-year storm event.
The storm water runoff in a portion of the roadside ditches of Williams Creek Drive will
discharge into an improved drainage channel to convey the water from the street right-of-way
to Detention Pond No 1. The channel will have a concrete flume in the bottom to control
erosion. Appendix C contains a summary of the channel design parameters and calculations.
The velocity for the design storm event, the 25-year storm, is 3.0 fps for Channel No . 9.
Although it is not required, a concrete flume is proposed for the bottom of the channel to
prevent erosion. Appendix C contains the channel calculator data for the 25-and 100-year
storm events.
Johnson Creek Loop will be constructed with temporary turnarounds at each end for Phase 2.
The roadside ditches and these turnarounds will be constructed to drain in a controlled manner
to the existing ground. The north end of the loop will have a channel constructed to spread out
the flow and reduce the velocity before the runoff enters the existing dense vegetation. The
roadside ditches at the south end of the loop will discharge into a ditch which will also
JO
discharge into dense vegetation. The existing dense vegetation should adequately prevent
erosion at the ditch discharge locations.
The velocity of the flow in the roadside ditches was evaluated for the 10-year and 100-year
stom1 events. The drainages are shown on Exhibit D.
The city requirements for ditch lining material are as follows:
Maximum Design Velocities of Various
Surface Treatments'
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.
CONCLUSIONS
The construction of this project will increase the storm water runoff from this site. However,
some of the runoff will be carried through a drainage system to existing drainage channels and
then directly to Carters Creek and 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. The portion of the site which flows to Lick Creek will have detention
facilities to reduce the post-development flows to pre-development values. No flood damage to
downstream or adjacent landowners is expected as a result of this development.
11
APPENDIX A
Time of Concentration Equations & Calculations
12
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.10
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.04
. 02 -
.01 -
.005 ' 1
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6
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Average velocity, ft/sec
~
~·
~ .
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7
7
I I
10
. . .
Fiicu~ :1-1.-Averaice velocities for e•timatinic trJvel time for •hallow concentrated now.
(210-VI-TR-55. Second Ed., June 198G)
I
20
-i
Tc Calculations-Pre-Development (Pond)
Drainage Area #101
Sheet Flow:
L= 240
n=
P=
0.007(L*nt" =
(P)o s*(S)o4
Concentrated Flow:
L= 618
U(60*V)
Drainage Area #102
Sheet Flow:
L= 240
V=
n=
P=
0.007(L*nt" =
(P)°"s*(S)o4
Concentrated Flow1 : V=
L= 232
U(60*V) =
Concentrated Flow2: V=
L= 242
L/(60*V)
Concentrated Flow3: V=
L= 606
L/(60*V)
0.4 (wooded)
4.5
0.654 hours=
2.2 fps (unpaved)
4.7 min
43.9 min
0.4 (wooded)
4.5
0.593 hours=
2 fps (unpaved)
1.9 min
2.5 fps (unpaved)
1.6 min
1.8 fps (unpaved)
5.6 min
44.7 min
39 .2 min
35.6 min
278 Slope= 0.017
267 Slope= 0.018
279.4 Slope= 0.021
276 Slope= 0.015
270 Slope= 0.025
263 Slope= 0.012
Tc Calculations-Post-Development (Pond)
Drainage Area #201
Sheet Flow:
L= 132
n=
P=
0.007(L*n(0 =
(P)os*(S)o4
Concentrated Flow 1: V=
L= 626
L/(60*V) =
Concentrated Flow 2: V=
L= 200
L/(60*V)
Concentrated Flow 3: V=
L= 131
L/(60*V) =
Concentrated Flow 4: V=
L= 100
L/(60*V)
Concentrated Flow 5: V=
L= 50
L/(60*V)
Concentrated Flow 6: V=
n=
L= 350
L/(60*V)
Concentrated Flow 6: V=
n=
0.24 (dense grass)
4.5
Elev1= 281 .5 Slope=
0.238 hours= 14.3 min
1.25 fps (unpaved)
Elev1=
8.3 min
1.7 fps (unpaved)
2.0 min
1.25 fps (unpaved)
Elev1=
1.7 min
1.45 fps (unpaved)
Elev1=
1.1 min
7.9 fps (through pipe)
Elev1=
0.1 min
4.36 fps (through channel)
0.014
Elev1=
1.3 min
1.53 fps (through pond)
0.035
333 Slope=
329 Slope=
327.82 Slope=
323 Slope=
Slope=
Slope=
0.023
0.006
0.011
0.006
0.008
0.011
0.006
L= 200
U(60*V)
Drainage Area #202
Sheet Flow:
L= 240
n=
P=
0.007(L*nt 0 =
(P)os*(S)oA
Concentrated Flow 1 : V=
L= 314
U(60*V) =
Concentrated Flow 2: V=
L= 200
U(60*V)
Drainage Area #203
Sheet Flow: n=
P=
L= 30
0.007(L*nt 0 =
(P)o s*(S)oA
Concentrated Flow 1: V=
L= 596
U(60*V) =
2.2 min
29.0 min
0.24 (dense grass)
4.5
0.458 hours=
2.5 fps (unpaved)
2.1 min
1.9 fps (unpaved)
1.8 min
31.4 min
0.24 (dense grass)
4.5
0.046 hours=
2.45 fps (unpaved)
4.1 min
6.9 min
Slope= 0.006
277.5 Slope= 0.015
27.5 min
270 Slope= 0.024
267.5 Slope= 0.013
278 Slope= 0.073
2.8 min
266 Slope= 0.024
Drainage Area #204
Sheet Flow: n=
P=
L= 240
0.007(L*nt0 =
(P)os*(S)oA
Concentrated Flow 1: V=
L= 476
U(60*V)
0.24 (dense grass)
4.5
Elev1=
0.397 hours=
2 fps (unpaved)
Elev1=
L 4.0 min
27.8 min
269.5 Slope= 0.021
23.8 min
262.5 Slope= 0.015
Drainage Area #27
Sheet Flow:
L= 132
Ti= 0.007(L *nt°
(P)os*(S)oA
Conce ntrated Flow 1:
L= 626
Ti= U(60*V)
Concentrated Flow 2:
L= 200
Ti= L/(60*V)
Concentrated Flow 3:
L= 131
Ti= U(60*V)
Concentrated Flow 4:
L= 100
Ti= L/(60*V)
Drainage Area #34
Sheet Flow:
L= 200
0.007(L*n(0
(P)os*(S)o4
Concentrated Flow 1:
L= 355
n=
P=
V=
V=
V=
V=
n=
P=
V=
0.15 (short grass prairie)
4.5
Elev,= 284.5 Elev2=
0 .1 63 hours= 9.8 min
1.25 fps (unpaved)
Elev,= 281 .5 Elev2=
8.3 min
1. 7 fps (unpaved)
Elev,= 333 Elev2=
2.0 min
1.25 fps (unpaved)
Elev,= 329 Elev2=
1.7 min
1.45 fps (unpaved)
Elev,= 327.82 Elev2=
1.1 min
22.9 min
0.15 (short grass prairie)
4.5
280 Elev2=
0.166 hours= 10 min
4.2 fps (unpaved)
281 .5 Slope=
333 Slope=
329 Slope=
327 .82 Slope=
323 Slope=
270 Slope=
270 Elev2= 245.9 Slope=
0.023
0.006
0.011
0.006
0.008
0.050
0.068
T,= L/(60*V) = 1.4 min
Concentrated Flow 2: V= 2 fps (unpaved)
L= 25 Elev1= 245.9 Elev2= 245.5 Slope= 0.016
T,= L/(60*V) 0.2 min
Concentrated Flow 3: V= 1.25 fps (unpaved)
L= 600 Elev1= 245.5 Elev2= 241 .9 Slope= 0.006
T,= L/(60*V) 8.0 min
Concentrated Flow 4: V= 2.4 fps (unpaved)
L= 200 Elev1= 241 .9 Elev2= 237.5 Slope= 0.022
T,= L/(60*V) 1.4 min
Concentrated Flow 5: V= 2.8 fps (unpaved)
L= 250 Elev1= 237.5 Elev2= 230 Slope= 0.030
T,= L/(60*V) = 1.5 min
V= 1.45 fps (unpaved)
L= 220 Elev1= 230 Elev2= 228.2 Slope= 0.008
T,= L/(60*V) 2.5 min
I Tc= 25.0 min
Drainage Area #35
Sheet Flow: n= 0.15 (short grass prairie)
P= 4.5
L= 63 Elev1= 247.8 Elev2= 247.4 Slope= 0.006
T,= 0.007(L *n(0 0.151 hours= 9.1 min
(P)os*(S)oA
Concentrated Flow 1: V= 2.2 fps (unpaved)
L= 100 Elev1= 247.4 Elev2= 245.5 Slope= 0.019
T,= L/(60*V) 0.8 min
Concentrated Flow 2: V= 1.25 fps (unpaved)
L= 600 Elev1= 245.5 Elev2= 241.9 Slope= 0.006
T,= L/(60*V) = 8.0 min
Concentrated Flow 3: V= 2.4 fps (unpaved)
L= 200 Elev1= 241 .9 Elev2= 237.5 Slope= 0.022
T,= L/(60*V) 1.4 min
Concentrated Flow 4: V= 2.8 fps (unpaved)
L= 250 Elev1= 237.5 Elev2= 230 Slope= 0.030
T,= L/(60*V) 1.5 min
V= 1.45 fps (unpaved)
L= 220 Elev1= 230 Elev2= 228.2 Slope= 0.008
T,= L/(60*V) 2.5 min
ITc= 23.3 min
Drainage Area #135B
Concentrated Flow 1: V=
L= 700
T,= L/(60*V) =
Drainage Area #135C
Concentrated Flow 2: V=
L= 200
T,= L/(60*V)
Drainage Area #135D
Concentrated Flow 3: V=
L= 128
T,= L/(60*V) =
Drainage Area #133B
Sheet Flow: n=
P=
L= 132
0.007(L *n)' =
(P)o s*(S)o4
Concentrated Flow 1: V=
L= 626
L/(60*V)
Tc Calculations-Post Development
1.25 fps (unpaved)
Elev1= Elev2=
9.3 min
I Tc= 9.3 min
1.7 fps (unpaved)
Elev1= Elev2=
2.0 min
ITc= 11 .3 min
1.25 fps (unpaved)
Elev1= Elev2=
1.7 min
ITc= 13.0 min
0.15 (short grass prairie)
4.5
0 .163 hours= 9.8 min
1.25 fps (unpaved)
8.3 min
18.1 min
Slope= 0.006
Slope= ·0.011
Slope= 0.006
281 .5 Slope= 0.023
333 Slope= 0.006
Drainage Area #133C
Concentrated Flow 2: V=
L= 200
L/(60*V)
Drainage Area #133D
Concentrated Flow 3: V=
L= 131
L/(60*V)
Concentrated Flow 4: V=
L= 100
L/(60*V)
Drainage Area #1268
Sheet Flow: n=
P=
L= 176
0.007{L*n)' =
(P)o s*(S)o4
Concentrated Flow 1: V=
L= 358
L/(60*V)
Concentrated Flow 2: V=
L= 491
L/(60*V)
1.7 fps (unpaved)
Elev,=
2.0 min
20 .1 min
1.25 fps (unpaved)
Elev1=
1.7 min
1.45 fps (unpaved)
Elev1=
1.1 min
22.9 min
0.15 (short grass prairie)
4.5
Elev1=
329 Slope=
327.82 Slope=
323 Slope=
279.5 Slope=
0.188 hours= 11 .3 min
2.9 fps (unpaved)
Elev1= 267.68 Slope=
2.1 min
3.5 fps (unpaved)
Elev1= 244.13 Slope=
2.3 min
15.7 min
0.011
0.006
0.008
0.028
0.033
0.048
Drain age Area #130A
Concentrated Flow 1: V= 1.25 fps (unpaved)
L= 49 Elev1= Elev2= Slope= 0.006
Ti= L/(60*V) 0.7 min
IT0= 0.7 min
Drai nage Area #1 308
Concentrated Flow 2: V= 2.2 fps (unpaved)
L= 105 Elev1= Elev2= Slope= 0.01 9
Ti= L/(60*V) 0.8 min
ITc= 1.5 min
Drainage Area #130C
Concentrated Flow 2: V= 1.25 fps (unpaved)
L= 479 Elev1= Elev2= Slope= 0.006
Ti= L/(60*V) 6.4 min
IT0= 7.9 min
Drainage Area #130D
Concentrated Flow 2: V= 2.4 fps (unpaved)
L= 208 Elev1= Elev2= Slope= 0.022
Ti= L/(60*V) 1.4 min
ITc= 9.3 min
Drainage Area #130E
Concentrated Flow 2: V= 2.8 fps (unpaved)
L= 267 Elev1= Elev2= Slope= 0.030
Ti= L/(60*V) 1.6 min
ITc= 10.9 min
Drainage Area #130F
Concentrated Flow 2: V=
L= 259
L/(60*V)
Drainage Area #131A
Sheet Flow:
L= 200
n=
P=
0.007(L*n)' =
(P)o s*(S)o4
Concentrated Flow 1: V=
L= 353
L/(60*V)
Drainage Area #131 B
Sheet Flow:
L= 200
n=
P=
0.007(L*nl' =
(P)o s*(S)o4
Concentrated Flow 1 : V=
L= 353
L/(60*V)
Drainage Area #131C
Concentrated Flow 2: V=
L= 530
L/(60*V)
1.4 fps (unpaved)
3.1 min
14.0 min
0.15 (short grass prairie)
4.5
Slope=
267.5 Slope=
0.173 hours= 10.4 min
4.1 fps (unpaved)
1.4 min
11.8 min
0.15 (short grass prairie)
4.5
248.3 Slope=
269.5 Slope=
0.173 hours= 10.4 min
4.1 fps (unpaved)
245.9 Slope=
1.4 min
11 .8 min
1.25 fps (unpaved)
Slope=
7.1 min
18.9 min
0.008
0.045
0.054
0.045
0.067
0.006
Drainage Area #131 D
Concentrated Flow 3: V= 2.4 fps (unpaved)
L= 187 Elev1= Elev2= Slope= 0.022
T,= L/(60*V) 1.3 min
I Tc= 20.2 min
Drainage Area #131 E
Concentrated Flow 4: V= 2.8 fps (unpaved)
L= 240 Elev,= Elev2= Slope= 0.030
T,= L/(60*V) 1.4 min
ITc= 21 .6 min
Drainage Area #131 F
Concentrated Flow 5: V= 1.45 fps (unpaved)
L= 252 Elev,= Elev2= Slope= 0.008
T,= L/(60*V) 2.9 min
ITc= 24.5 min
APPENDIXB
Storm Sewer Culvert Data & Design Calculations
26
Williams Creek Subdivision -Phase 2
Culvert Summary
Size Length Slope Inlet Invert
Culvert # Elev
(in) (ft) (%) (ft)
8 18 44.0 2.14 246.98 -------------------
9 18 44.0 1.70 268.43 ----10 24 40.0 1.00 270.81
Outlet
Invert Elev
(ft)
246.0 --
267.7 ---
270.4
Top of Road
10 year storm 100 year storm
Design Flow v,. HW Design Flow V100 HW
(ft) (cfs) (fps) (ft) (cfs) (fps) (ft)
250.28 2.20 5.7 247.7 2.97 6.4 247.9 ---
271.73 5.01 6.8 269.7 6.75 7.3 270.0 ---
275.20 11 .10 3.5 272.7 15.10 7.3 273.1
Culvert 10 -10 Year Storm
Culv ert Calculator
Entered Data:
Shape .......................... .
Number of Barrels .............. .
Sol ving for .................... .
Chart Number ................... .
Sc ale Number ................... .
Chart Description .............. .
Scale Descript i on .............. .
Overtopping .................... .
Flowrate ....................... .
Manning 's n .................... .
Roadway Elev ati on .............. .
Inlet Elevation ................ .
Outlet Elev atio n ............... .
Diameter ....................... .
Length ......................... .
Entrance Loss .................. .
Tailwater ...................... .
Computed Results:
Headwater ...................... .
Slope .......................... .
Veloci t y ....................... .
Circul ar
1
Headwater
1
1
CONCRETE PIPE CULVERT; NO BEVELED RING ENTRANCE
SQUARE EDGE ENTRANCE WITH HEADWALL
Off
11.1000 c f s
0. 014 0
275.2 000 ft
270.810 0 ft
270.4100 ft
24.0000 in
40.0000 ft
0.0000
2 .0000 ft
272.7152 ft Outlet Control
0.010 0 ft/ft
3.533 2 fps
Culvert 10 -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 ............... .
Di ameter ....................... .
Length ......................... .
Entrance Loss .................. .
Ta ilwater ...................... .
Computed Results:
Headwater ...................... .
Slope .......................... .
Vel ocity ....................... .
Williams Creek Subdivision -Phase 2
College Station, Texas
Circular
1
Headwater
1
1
CONCRETE PIPE CULVERT ; NO BEVELED RING ENTRANCE
SQUARE EDGE ENTRANCE WITH HEADWALL
Off
15.1000 cfs
0. 0140
275.2000 ft
270.8100 ft
270.4100 ft
24 .0000 in
40 .0000 ft
0 .0000
2.0000 f t
273 .0686 ft I nlet Control
0.0100 ft /ft
7.2791 fps
Culvert 8 -10 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 ............... .
Di ameter ....................... .
Length ......................... .
Entrance Loss .................. .
Tailwater ...................... .
Computed Results:
Headwater ...................... .
Slope .......................... .
Velocity ....................... .
Circular
1
Headwater
1
1
CONCRETE PIPE CULVERT; NO BEVELED RING ENTRANCE
SQUARE EDGE ENTRANCE WI TH HEADWALL
Off
2.2 000 cfs
0. 0140
250.2800 ft
246.9800 ft
246.0400 ft
18 .0000 in
44.0000 ft
0 .0000
1.5000 ft
247.7469 ft Inlet Control
0.0214 ft/ft
5.8564 fps
Culvert 8 -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 .......................... .
Velocity ....................... .
Williams Creek Subdivision -Phase 2
College Station, Tex as
Circular
1
Headwater
1
1
CONCRETE PIPE CULVERT; NO BEVELED RING ENTRANCE
SQUARE EDGE ENTRANCE WITH HEADWALL
Off
2.9700 cfs
0. 0140
250 .2800 ft
246.98 00 ft
246.040 0 ft
18.0000 in
44.0000 ft
0.0000
1.5000 ft
247 .8960 f t Inlet Control
0 .0214 ft/ft
6.3790 fps
Culvert 9 -10 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 .......................... .
Velocity ....................... .
Circular
1
Headwater
1
1
CONCRETE PIPE CULVERT; NO BEVELED RING ENTRANCE
SQUARE EDGE ENTRANCE WITH HEADWALL
Off
5.0100 cfs
0. 0140
271.7300 ft
268.4300 ft
267.6800 ft
18.0000 in
44.0000 ft
0.0000
1.5000 ft
269.7112 ft Inlet Control
0.0170 ft/ft
6.7721 fps
Culvert 9 -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 .......................... .
Velocity ....................... .
Williams Creek Subdivision -Phase 2
College Station, Texas
Circular
1
Headwater
1
1
CONCRETE PIPE CULVERT; NO BEVELED RING ENTRANCE
SQUARE EDGE ENTRANCE WITH HEADWALL
Off
6.7300 cfs
0. 0140
271.7300 ft
268.4300 ft
267.6800 ft
18 .0000 in
44.0000 ft
0.0000
1.5000 ft
270.0088 ft Inlet Control
0.0170 ft/ft
7.3024 fps
APPENDIXC
Drainage Channel Design Data & Calculations
31
Williams Creek Subdivision -Phase 2
Channel Summary
Channel Bottom Width Side Slopes
#
(in) (H:V)
9 0 4:1
"V" Bottom Ditch
Slope
(%)
0.60
25 year storm 100 year storm
Design Flow Depth V2s Design Flow Depth V100
(cfs) (in) (fps) (cfs) (in) (fps)
13.43 12.8 3.0 15.93 13.6 3.1
Channel 9 -25 Year Storm
Channel Calculator
Given I nput Data :
Shape .......................... .
Solving for .................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Height ......................... .
Bottom width ................... .
Left slope ..................... .
Right slope .................... .
Computed Results :
Depth .......................... .
Velocity ....................... .
Flow area ...................... .
Flow perimeter ................. .
Hydraulic radius ............... .
Top width ...................... .
Area ........................... .
Perimeter ...................... .
Percent full ................... .
Trapezoidal
Depth of Flow
13. 4300 cfs
0.0060 ft/ft
0.0250
36.0000 in
0.0000 in
0 .2500 ft/ft
0.2500 ft/ft
12.7733 in
2.9633 fps
4 .5321 ft2
105.3313 in
6.1960 in
102.1864 in
36.0000 ft2
296.8636 in
35.4814 %
Channel 9 -100 Year Stor m
Channel Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Height ......................... .
Bottom width ................... .
Left slope ..................... .
Right slope .................... .
Computed Results:
Depth .......................... .
Velocity ....................... .
Flow area ...................... .
Flow perimeter ................. .
Hydraulic radius ............... .
Top wi dth ...................... .
Area ........................... .
Perimeter ...................... .
Percent full ................... .
Williams Creek Subdivision -Phase 2
College Station, Texas
Trapezoidal
Depth of Flow
15.9300 cfs
0 .0060 ft/ft
0 .0250
36.0000 i n
0.0000 i n
0.2500 ft/ft
0.2500 ft/ft
13.6178 in
3.0925 fps
5 .1512 ft2
112.2948 in
6.6056 in
108.9420 i n
36.0000 ft2
296.8636 in
37.8271 %
APPENDIXD
Drainage Ditch Data & Lining Material
34
Williams Creek Drive
Left Ditch
From To Slope Station Station
24+90.00 25+16.30 4.87%
25+16.30 26+14.79 1.64%
26+14.79 26+21 .22 50.00%
26+21 .22 28+00.00 4.59%
28+00.00 29+50.00 5.75%
29+50.00 30+00.00 4.21 %
30+00.00 30+75.00 2.92 %
30+75.00 31+50.00 1.24 %
31+50.00 32+56.29 -0.40%
32+56.29 34+00.00 0.81%
34+00.00 35+48.89 -0.60 %
Johnson Creek Loop
Left Ditch
From To
Station Station
0+37.00 1 +00 .00
1 +00.00 2+00.00 -2+00.00 7+00.00
7+00.00 9+00.00 ---9+00.00 11+50.00 --11 +50.00 13+69.33 -· --~-38+30.70 39+00.00 --39+00.00 46+00.00 ----46+00.00 48+00.00 ----·--48+00.00 49+13.51
Old May Court
Left Ditch
From To
Station Station
0+25.14 0+50.00 -----0+50.00 1 +00.00
1 +00.00 4+80.52
Slope
-0.60%
-1 .94%
-0.60%
-2.20%
-3 .00% --0 .80% ---0.60% ---0.60% --1 .11 %
-0.60%
Slope
11 .93% ·--4.69%
0.60%
Drainage 0 10 V10 0 100 V100 Ditch Lining Material Area#
132A-F 2.59 3.35 3.49 3.60 Grass-seeded
132A-F 2.59 2.22 3.49 2.40 Grass-seeded
132A-E 1.94 7.45 2.62 8.04 Conc-Riprap
132A-E 1.94 3.04 2.62 3.28 Grass-seeded
132A-D 1.21 2.94 1.63 3.17 Grass-seeded
132A-C 0.69 2.28 0.93 2.45 Grass-seeded
132A-B 0.52 1.85 0.70 1.99 Grass-seeded
132A 0.27 1.14 0.36 1.22 Grass-seeded
134 1.01 1.04 1.37 1.12 Grass-seeded
133A-D 10.93 2.44 14.87 2.64 Grass-seeded
135A-D 3.46 1.64 4.68 1.77 Grass-seeded
Drainage 0 10 V10 0 100 V100 Ditch Lining Material Area#
130A 0.17 0.77 0.23 0.83 Grass-seeded
130A-B 0.56 1.62 0.76 1.74 Grass-seeded
130A-C 2.24 1.47 3.03 1.59 Grass-seeded
130A-D 2.94 2.56 3.96 2.76 Grass-seeded --130A-E 3.79 3.10 5.11 3.31 Grass-seeded --130A-F 4.42 1.94 5.98 2.40 Grass-seeded ----135A 0.35 0.93 0.47 1.00 Grass-seeded -----135A-B 2.68 1.54 3.61 1.66 Grass-seeded --135A-C 3.16 2.02 4.26 2.18 Grass-seeded
13 5A-i5 --------3.46 1.64 4.68 1.77 Grass-seeded
Drainage 0 10 V10 0100 V 100 Ditch Lining Material Area#
125 5.01 5.52 6.75 5.95 Conc-Rjprap
125 5.01 3.89 6.75 4.19 Grass-seeded
125 5.01 1.80 6.75 1.94 Grass-seeded
Williams Creek Drive
Right Ditch
From To Slope Station Station
24+90.00 25+16.30 4.87%
25+16.30 28+00.00 4.59%
28+00.00 29+50.00 5.75%
29+50.00 29+72.51 2.68%
29+72 .51 30+27.76 1.35%
30+27 .76 30+34.19 50.00%
30+34.19 30+75.00 2.92%
30+75.00 31 +50.00 1.24%
31 +50.00 32+56.29 -0.96%
32+56.29 34+00.00 1.22%
34+00.00 35+48.89 -0.60%
Johnson Creek Loop
Right Ditch
From To
Station Station
0+37.00 1+00.00
1+00.00 2+00.00
2+00.00 7+00.00
7+00.00 9+00.00
9+00.00 11 +50.00
11+50.00 13+69.33 -· -38+30.70 39+00.00 ..
39+00.00 46+00.00 --46+00.00 48+00.00 --48+00.00 49+13.51
Old May Court
Right Ditch
From To
Station Station
0+25.14 0+50.00
0+50.00 1+00.00
1+00.00 4+80.52
Slope
-1.85%
-1 .94%
-0.60%
-2 .20%
-3.00% ---0.80% ---0.60%
-0.60%
-1 .11%
-0.60%
Slope
12.93% --5.69%
0.60%
Drainage
Area#
126A-C
126A-C
126A&C
125
125
125
138
138
138
137
136
Drainage
Area#
131A
131A-B
131A-C
131A-D -131A-E --131A-F -133A
133A-B
133A-C
133A-D
Drainage
Area#
126A
126A
126A
0 10 V10 0 100 V 100 Ditch Lining Material
16.36 5.30 22.14 5.72 Grass-Sodded
16.36 5.19 22.14 5.60 Grass-Sodded
3.50 3.84 4.71 4.14 Grass-seeded
5.01 3.15 6.75 3.40 Grass-seeded
5.01 2.44 6.75 2.63 Grass-seeded
5.01 9.45 6.75 10.18 Conc-Riprap
0.39 1.73 0.52 1.87 Grass-seeded
0.39 1.26 0.52 1.35 Grass-seeded
0.39 1.14 0.52 1.23 Grass-seeded
0.52 1.33 0.70 1.44 Grass-seeded
0.22 0.83 0.29 0.89 Grass-seeded
0 10 V10 0 100 V 100 Ditch Lining Material
3.26 2.47 4.40 2.66 Grass-seeded
8.16 3.16 11.02 3.40 Grass-seeded
26.52 3.73 35 .98 2.95 Grass-seeded
27.92 4.50 37 .91 4.86 Grass-Sodded
30.11 5.15 40.92 5.56 Grass-Sodded
43.89 3.45 59.77 3.73 Grass-seeded -0.73 1.11 0.99 1.20 Grass-seeded
9.46 2.11 12.82 2.28 Grass-seeded -10.00 2.69 13.58 2.91 Grass-seeded
10.93 2.19 14.87 2.36 Grass-seeded
0 10 V10 0 100 V100 Ditch Lining Material
2.16 4.61 2.91 4.97 Conc-Riprap
2.16 3.39 2.91 3.65 Grass-seeded
2.16 1.46 2.91 1.57 Grass-seeded
APPENDIXE
Detention Pond Design Information
37
Drainage Area -101
Area -Ac.
sq. mi.
8.11
0.0127
Tc = 43.9
Lag = L = 0.6Tc =
Land Use
Gravel Road
Woods-Good
Pasture-Fair
Total -CN II
26.3 min=
Area -Ac.
0.13
6.38
1.60
8.11
Average Runoff condition CN =
CN I= 61 .2
ARC CN = CN I+ 0.70(CN II -CN I)
SCS Curve Number Calculations
Pond-Pre-Development
Drainage Area -102
Area -Ac. 17 .74
sq. mi. 0.0277
Tc = 44.7
0.439 hrs Lag = L = 0.6Tc = 26.8 min=
Weighted
CN II CN Land Use Area -Ac.
89 1.4 Gravel Road 0.12
77 60.6 Woods-Good 14.10
84 16.6 Pasture-Fair 3.52
78.6 Total -CN II 17.74
73.4 Average Runoff condition CN =
CN I= 61
ARC CN = CN I+ 0.70(CN II -CN I)
0.447 hrs
Weighted
CN II CN
89 0.6
77 61 .2
84 16.7
78.5
73.2
Drainage Area -201
Area -Ac.
sq. mi.
8.93
0.0140
Tc= 29 .0
Lag= L = 0.6Tc = 17.4 min=
Land Use Area -Ac.
1 Acre Residential Lots
Pasture-Fair
Total -CN II
Average Runoff condition CN =
CN I= 68
ARC CN = CN I + 0.70(CN II -CN I)
Drainage Area -203
Area -Ac.
sq . mi.
0.96
0.0015
Tc = 10.0
Lag = L = 0.6Tc = 6.0 min=
6.40
2.53
8.93
Land Use Area -Ac.
Gravel Road
Pasture-fair
Total -CN II
Average Runoff condition CN =
CN I= 69.4
ARC CN = CN I + 0.70(CN II -CN I)
0.14
0.82
0.96
SCS Curve Number Calculations
Pond-Post Development
0.29 hrs
Weighted
CN II CN
84 60.2
84 23.8
84.0
79.2
0.1 hrs
Weighted
CN II CN
89
84
80.1
13.0
71.8
84.7
Drainage Area -202
Area -Ac.
sq. mi.
10.13
0.0158
Tc= 31.4
Lag= L = 0.6Tc = 18.8 min=
Land Use Area -Ac.
1 Acre Lots 6.02
Wooded-good 3.29
Pasture-Fair 0.82
Total -CN II 10.13
Average Runoff condition CN =
CN I= 65.4
ARC CN = CN I+ 0.70(CN II -CN I)
Drainage Area -204
Area -Ac. 5.29
sq . mi . 0.0083
Tc = 27.8
Lag = L = 0.6Tc = 16.7min=
Land Use Area -Ac.
Gravel Road
Wooded-good
Pasture-fair
Total -CN II
Average Runoff condition CN =
CN I= 61 .6
0.18
4.09
1.02
5.29
ARC CN = CN I + 0.70(CN II -CN I)
0.314 hrs
Weighted
CN II CN
84 49.9
77 25.0
84 6.8
81.7
76.8
0.278 hrs
Weighted
CN II CN
89 3.0
77 59.5
84 16.2
78 .8
73.6
Detention Pond No. 1 Area-Capacity Data
V = H * {[A1+A2 + (A1*A2)112] / 3}
V = volume, ft2
A = area, ft2
H = difference in elevation, ft
POND N0.1
Elevation Depth Area
(ft) (ft) (ft2)
267.00 0.00 0
268.00 1.00 12613
269.00 2.00 24174
270.00 3.00 29279
271.00 4.00 51918
Area -Capacity Data
Area Volume Cumulative
Volume
(acres) (ac-ft) (ac-ft)
0.000 0.000 0.000
0.290 0.097 0.097
0.555 0.415 0.512
0.672 0.613 1.124
1.192 0.920 2.044
90 % Cumulative
Volume
(ac-ft)
0.000
0.087
0.460
1.012
1.840
Williams Creek Subdivision -Phase 2
Detention Pond No. 1 Outlet Structure and Pipe
Outlet Structure -3' x 3' inner diameter riser box
Box crest at 270.0'
Opening = 15" wide x 36" high, FL = 267 .0
Weir L = 1.25'
Outlet Pipe -27" RCP@ 1.0% with concrete S.E.T. at outlet
Elevation -Discharge Data
Weir Q, Overt op Q, Elevation Depth Weir Weir Depth Weir (12' perimeter)
(ft) (ft) (cfs) (ft) (cfs)
267 0 0 0 0
268 1.0 3.7 --
269 2.0 10.6 --
270 3.0 19.5 --
271 4.0 19.5 1.0 36.0
* Pipe flow is limiting discharge at this elevation.
Inlet Control
Culvert
Depth Q
(ft) (cfs)
0 0
1 4.2
2 15.2
3 24.4
4 31 .5
Max
Total Q
(cfs)
0
3.7
10.6
19.5
* 31 .5
Detention Pond No. 2 Area-Capacity Data
V = H * {[A1+A2 + (A1 *A2)112] / 3}
V = volume, ft2
A= area, ft2
H = difference in elevation, ft
POND NO. 2
Elevation Depth Area
(ft) (ft) (ft2)
267.00 0.00 0
268.00 1.00 5418.74
269.00 2.00 25,063.57
270.00 3.00 56,884.54
271 .00 4.00 87,937.27
Area -Capacity Data
Area Volume Cumulative
Volume
(acres) (ac-ft) (ac-ft)
0.0000 0.0000 0.0000
0.1244 0.0415 0.0415
0.5754 0.3224 0.3639
1.3059 0.9160 1.2799
2.0188 1.6494 2.9294
90 % Cumulative
Volume
(ac-ft)
0.0000
0.0373
0.3275
1.1519
2.6364
Williams Creek Subdivision -Phase 2
Detention Pond No. 2 Outlet Pipe
27" RCP @ 1.0% with concrete S.E.T.'s
Elevation -Discharge Data
Inlet Control
Elevation Culvert
Depth Q
(ft) (ft) (cfs)
267 0 0
268 1 4.2
269 2 15.2
270 3 24.4
271 4 31 .5
EXHIBIT A
Drainage Area Map -Pre-Development Detention Pond
44
EXHIBIT B
Drainage Area Map -Post-Development Detention Pond
46
EXHIBIT C
Drainage Area Map -Post-Development
48
EXHIBIT D
Drainage Area Map -Post-Development Ditch Velocities
50