HomeMy WebLinkAboutDrainage ReportDRAINAGE REPORT
FOR
AllSaf e Storage
13101 Wellborn Road
IN
COLLEGE STATION, TEXAS
OCTOBER, 2002
Revised on October 29, 2002
REVIEWED FOR
COMPLIANCE
NOV 2 6 2002
COLLEGE STATION INOINEEAING
SITECH ENGINEERING CORPORATION
1544 SAWDUST ROAD #100
THE WOODLANDS, TEXAS 77380
(281) 363-4039
PROJECT NO. 2311-001
CERTIFICATION
"I hereby certify that this report (plan) for the drainage design of AllSafe Storage was
prepared by me (or under my supervision) in accordance with the provisions of the City
of College Station Drainage Policy and Design Standards for the owners thereof."
Registered Professional
State of Texas No.: 8 ~~~-~
DRAINAGE STUDY
FOR
ALLSAFE STORAGE
13101 WELLBORNROAD
COLLEGE STATION, TEXAS
JOB NO. 2311-001
I. LOCATION AND DESCRIPTION
M.P. Texas Properties, LLC proposes to develop 6.182 acres in the Edelweiss Business Center,
Lot 2, 3, 4, and 5, Block 1 along FM 2154 (Wellborn Road) as a mini-storage facility. The
location of the AllSafe Storage site is shown in Exhibit "A" on the United States Geologic
Survey (U.S.G.S.) Topographi.c Quadrangle Map. The site is adjacent to the Shadow Rock Pet
Resort on the southeast and the Edelweiss Estates residential subdivision on the northeast. The
site is gently sloping towards FM 2154 and is covered with tall grass and a few trees. The soils
are silty sand and lean clay above fat clay and lean clay. There is an existing roadside ditch
adjacent to FM 2154 that is flowing to the southeast. There is an existing 24" culvert under FM
2154 and the railroad tracks about 150 feet south of the property line that conveys water to
Hopes Creek, see Exhibit "B" on the City of College Station aerial topographic map. The
AllSafe Storage site is in the Hopes Creek Drainage Basin. The proposed mini-storage
development will consist of buildings, paving, and landscaping. The purpose of this report is to
identify and define conceptual solutions to the problems that may occur on-site and off-site as a
result of the development.
II. DRAINAGE BASINS AND SUB-BASINS
The primary drainage basin is Hopes Creek. According to the FEMA Flood Insurance Rate Map
Number 48041C0182C effective July 2, 1992, the project site is in Zone "X", areas determined
to be outside the 500-year floodplain. Portions of the FIRM Panel are presented in Appendix A.
There is a small offsite area that drains through the site as part of the natural drainage pathway.
This offsite area is approximately 0.538 acres of the adjacent residential subdivision to the
northeast. The concrete masonry wall required at the rear of the property adjacent to an existing
wood fence will have weepholes every 30 feet along the wall to allow the small offsite area to
continue to drain towards FM 2154.
III. DRAINAGE DESIGN CRITERIA
The detention basin is designed to limit the postdeveloped discharge rates to the predeveloped
condition discharge rate for the 25-year design storm. The development of the property impacts
the drainage of the area by increasing the amount of storm water runoff from the site and altering
the drainage pathways. Flows that were previously discharged into the roadside ditch over the
entire property frontage in the predeveloped condition now are discharged at one point from the
detention basin for the developed condition.
The calculations for the detention basin and conveyance system are summarized below.
Appendix B contains the complete calculations. In order to determine the required volume of
and the allowable discharge rate from the detention basin, the peak discharge flowrates for the
25-year design storm were calculated. The peak discharge for both the pre-developed and
developed conditions during the 25-year storm was calculated using the Rational Formula (Q =
2311-001 Page 1 of 4 Pages
,
DRAINAGE STUDY ADDENDUM
FOR
ALLSAFE STORAGE
13101 WELLBORN ROAD
COLLEGE STATION, TEXAS
JOB NO. 2311-001
November 20, 2002
III. DRAINAGE DESIGN CRITERIA
The last sentence in the last paragraph of Section III is amended to read "An 18-inch diameter
orifice resulted in a discharge rate of 17 .81 cfs, which meets the criteria of being less than the
predeveloped discharge rate".
IV. DRAINAGE FACILITY DESIGN
The third to last sentence in the paragraph of Section IV is amended to read "The outfall pipe is
30-inches in diameter with an 18-inch orifice at the downstream end to restrict discharge rates
and a trash rack at the upstream end to prevent large debris from entering the outfall pipe."
APPENDIXB
The calculations spreadsheet labeled "College Station Drainage Criteria Manual Detention Basin
Calculations" is replaced with the attached with a revision date of November 19, 2002.
APPENDIXC
The full-size plans in Appendix C are replaced with the attached C-4,5,6, and 14B which have
been revised and were signed on November 20, 2002.
APPENDIXD
Appendix D is a new appendix that has been added to include the hydraulic gradeline
calculations for the detention basin outfall pipe.
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2311-001 Page 1 of 1 Pages
College Station Drainage Criteria Manual Detention Basin Calculations
Proiect: ALLSAFE STORAGE WELLBORN RD. TxDOT:
Job# 2311-001 Equations: Intensity •1• = bl(t+d) •
System: BRAZOS COUNTY 25 YR STORM b,. = 89
By: HJH Date: 8122102 d,. = 8.5
Rev: HJH Date: 11119102 e,. = 0. 754
Chkbv: WBP Date: Peak Runoff "Q" = C ,(CiA)
Cf= 1.10
Ale Name: 2311-001 DRAINAGE CALCS (product of C1(C) can not be greater than 1.0)
PRE-DEVELOPMENT
Area Site Area Runoff Time Cone. Intensity Runoff
Description (acres) "C,s" (min} '"125" Q25 in cfs
To Basin 6.182 0.39 17.6 7.608 18.11
Note: •c• value based on Natural Grasslands w/1" Slope (CSDramage Poftcy, Table 111-1)
POS~DEVELOPMENT(ULTIMATEJ
Area Site Area Runoff Time Cone. Intensity Runoff
Description (acres) "C,s" (min) "125" Q25 In els
To Basin 6.182 0.88 10 9.861 53.65
Note: •c• value based on Impervious Areas and Landscaped Areas w/1% Slope (CS Drainage Po/1Cy, Table l//--1)
DETENTION STORAGE vs. WATER SURFACE ELEVATION
Post-Development "CN" -Area Draining to Detention Basin
Tota/Area= 6.182 acres
Impervious Area =-= 4.95 acres
Landscaped Area = 1.24 acres
Total Acres = 6.182 acres
Average .. CN" = ("CN" 1 x Area 1 + .. CN" 2 x Area 2 + .... + "CN"; x Area;)
Tota/Area
Averaae "CN" = 93.8
Water Surface Area Area Detention Storage Detention Slorage
Elevation (s.f.) (acres) le.I.\ Cumulative <acre-feel\
325.50
325.00
324.00
323.00
322.00
321 .00
320.00
OUTFLOW CALCULATIONS
Orifice Equation
Q = C x Ax (2 x g x h)' 0.5
Q = Peak Outnow Discharge (els)
C = Orifice Coefficient =
A = Cross-sectional Area of Orifice
g =Gravitational coefficient=
h = Head on Orifice (ft.)
36,122
34,432
31,148
27,993
25,005
5,127 -
0.829 17638.71 2.791
0.790 32790.41 2.386
0.715 29570.91 1.633
0.643 26499.17 0.954
0.574 15066.00 0.346
0.118 2563.50 0.059
0.000
18 Inch Orifice Discharae Ploe
Try using orifice w/ diameter=
0. 7 Ortfice Flowllne =
Midpoint of orifice =
32.2 ft./sec2 Maximum W.S.E. c
TallwaterW.S.E. =
Head on Ortflce (hos In feet} = 3.22 17.81 cfs
CONVEYANCE CALCULATIONS FOR BASIN DISCHAGE PIPE
Type of Pipe: RCP
Discharge Mannings Length Nominal Hydraulic Grade% Velocity
from Orifice Eqtn. "n" (ft.} Pipe Size Radius (ft./ft.} (fps)
lets\ (In) (ft) Flowinq Full
17.81 0.013 52 30 0.6 0.00173 3.48
Top of Berm Is 325.50
25-yearWSE Is 325.00
18 Inches
320.09
320.84
325.00
321 .78 (High Bank of Stream@ Pond Outlet)
OK Allowable Discharge = 18.11
98
77
APPENDIXD
Hydraulic Gradeline Calculations for
Detention Basin Outfall
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SITECH ENGINEERING CORPORATION
ENGINEERS • PLANNERS • SURVEYORS
1544 SAWDUST RD., #100
THE WOODLANDS, TEXAS 77380
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---I I
SITECH ENGINEERING CORPORATION
ENGINEERS • PLANNERS •SURVEYORS
1544 SAWDUST RD., #100
THE WOODLANDS, TEXAS 77380
01-:z.1 1-00\
SITECH ENGINEERING CORPORATION
ENGINEERS• PLANNERS • SURVEYORS
1544 SAWDUST RD., #100
THE WOODLANDS, TEXAS 77380
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\ r\ R-_o°'-c\ s \~ \) \ 1-c\A
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 ................... .
Page 1
Trapezoidal
Depth of Flow
17.7900 cfs
0.0014 ft/ft
0.0450
2.0000 ft
0.0000 ft
0.1889 ft/ft (V/H)
0.2160 ft/ft (V/H)
1.7821 ft+3;;;,).o.oo-=Pd.1.·115}
1.1290 fps
24.1977 cfs
15.7577 ft2
18.0416 ft
0.8734 ft
17.6845 ft
19.8469 ft2
20.2477 ft
89.1047 %
EXHIBIT A
6.182-ACAE
EXISTING CONDmON SITE
BOUNDARY
SCALE
1· -2000'
ENGINEERING CORP.
·The Site Technology Group•
1544 SA'M>UST ROAD, SUITE 100
THE WOODLANDS, TEXAS 77380
OFF. ii (281) 363-4039 FAX ii (281) 363-3459
e-mail: secCsitecheng.com
O COPYRIGHT 2001
CiA). The runoff coefficient was calculated using a weighted average based on the type of
landcover for the predeveloped and developed conditions. The rainfall intensity was calculated
using the TXDOT coefficients for Brazos County in the equation (I= b/ (tc+dn. The time of
concentration (tc) for the predeveloped condition was calculated using the longest flowpath on
the site which consisted of 100 lineal feet of sheetflow, 320 feet of shallow concentrated flow,
and 640 lineal feet of ditch flow. The runoff coefficient was multiplied by a runoff factor (Cr ) of
1.10 for the 25-year storm. The contributing area for detention calculations is the site area of
6.182 acres. The peak discharge rates for the 25-year storm were calculated as 18.11 cfs for the
predeveloped condition, and 53.65 cfs for the developed condition. The detention basin was
designed to mitigate the affects of converting pervious surfaces to impervious by detaining the
stormwater runoff and controlling the release rate from the basin to not exceed 18.11 cfs.
The Triangular Approximation Method was used to determine the hydrograph for the site. The
Detention Basin Sizing Program (version 1.4) by Dodson & Associates, Inc. was used to
calculate the detention volume. The SCS Curve Number method was used to estimate the
volume of runoff from the site for the developed condition. The following assumptions are made
in the Detention Basin Sizing Program:
1. The inflow hydro graph of the detention basin is triangular, with one-third of the total
volume of runoff occurring prior to the peak flow rate.
2. The outflow hydro graph has the same volume as the inflow hydrograph.
3. The "minimum" condition outflow hydro graph is trapezoidal in shape.
The minimum required detention volume is represented by the shaded area in Figure 1 and
represents the volume of stormwater in excess of that which is released at the predeveloped peak
discharge rate of 18.11 cfs.
79
69
F 59
l
0
w 49
R a 39
t
e 29
19
9
9. 2. 3.
Tifl\e
Figure 1
Source: Detention Basin Sizing Program (version 1.4) by Dodson & Associates, Inc.
2311-001 Page 2 of 4 Pages
I I I
The minimum required detention volume calculated by the program was 1.8 acre-feet (see Figure
2). A factor of safety of 10% was added, increasing the volume to 1.98 acre-feet. The detention
basin was designed to provide 2.386 acre-feet of storage.
DETENTION BASIN SIZING
DETENTION BASIN SIZING BY TRIANGULAR HYDROGRAPHS
Detention Basin Drainage Area (acres) Peak Inf low Rate into Basin (cubic feet per second)
Peak Release Rate from Basin (cubic feet per second)
Total Inf low Uolume into Basin (acre-feet)
Available Storage Depth of Basin (feet)
Required Freeboard in Basin (feet) Side Slopes of Basin <horizontal/vertical)
Width of Maintenance Berm around Basin (feet)
*** RESULTS *** MINIMUM
REQUIRED DETENTION UOLUME <ACRE-FEET) Detention Uolume Per Acre (acre-feet per acre)
Basin Surface Area without Maint. Berm (acres)
Basin Surface Area with Maintenance Berm <acres) Basin Excavation Uolume (cubic yards)
1.8
0.29
0.?2
0.?2
3522
6.182
53.65
18.11
4.1489?5
3
.5
4
0
NORMAL
2.3
0.3?
0.88
0.88
4404
<Enter): Re eat, <R>e ort, (G)ra h, <P>rint Gra h, or <Esc): End
Figure 2
MAXIMUM
2.?
0.44
1.05
1.05
5285
Source: Detention Basin Sizing Program (version 1.4) by Dodson & Associates, Inc.
The Orifice Equation (Q = C x A x (2gh)0·5) was used to calculate the size of the orifice so that
detention basin outflow would be limited to the predeveloped discharge rate of 18 .11 cfs. An 18-
inch diameter orifice resulted in a discharge rate of 1 7 .19 cfs, which meets the criteria of being
less than the predeveloped discharge rate.
IV. DRAINAGE FACILITY DESIGN
The detention basin is located at the South end of the site and the conveyance system is designed
to convey the 25-year design storm to the detention basin (see Appendix C for drainage and
grading plans). The conveyance system consists of a valley in the concrete driveways flowing
towards curb inlets that are connected by pipe that discharges into the detention basin. The
detention basin is designed to drain dry with a concrete pilot channel at a 0.5% slope and a
transverse slope of 1.0% towards the pilot channel. The sides of the basin are sloped at 4:1. The
entire basin will be planted with grass after the grading has been completed. Water oaks will be
planted in the detention basin in order to meet the City's landscaping requirements for the site.
The 25-year water surface elevation is 325.00 and the top of the berm is 325 .50, providing 0.5
feet of freeboard. A 1 O' wide emergency overflow spillway is provided at elevation 325 .25 for
storms that exceed the detention volume capacity of the basin. The outfall pipe is 36-inches in
diameter with an 18-inch orifice at the upstream and downstream ends to restrict discharge rates.
A concrete chute will be installed at the end of the outfall pipe in the existing roadside ditch in
2311-00 l Page 3 of 4 Pages
order to mitigate erosion. The minimum finished floor elevation was established as eight inches
above the emergency overflow spillway elevation of 325.25. During the 100-year storm the
concrete valleys between the buildings are designed to have sufficient capacity to prevent the
buildings on the site from flooding (see Appendix B for calculations).
V. CONCLUSIONS
The detention basin was designed using the design guidelines outlined in the City of College
Station Drainage Policy and Design Standards. The conveyance system was designed to convey
stormwater during the 25-year design storm to the detention basin. The site was graded and
finished floor elevations were established in order to prevent flooding of the buildings during the
100-year storm event. When the storm sewer pipes are flowing full and water ponds in the
concrete valleys between the buildings, water will flow over the six-inch curb towards the
landscaped area adjacent to FM 2154 prior to reaching the finished floor elevations of the
buildings. When the volume of stormwater in the detention basin exceeds the 2.386 acre-feet of
storage available, stormwater will begin to flow over the emergency overflow spillway into the
existing roadside ditch on FM 2154.
23 11-001 Page 4 of 4 Pages
APPENDIX A
• NATIONAL FLOOD INSURANCE PROGRAM
FIRM
FLOOD INSURANCE RATE MAP
BRAZOS COUNTY,·
TEXAS AND
INCORPORATED AREAS
PANEL 182 OF 250
(SEE MAP INDEX FOR PANELS NOT PRINTED)
CONTAINS:
COMMUNITY
COLLEGE STATION, CITY OF
UNINCORPORATED AREAS
480083 0182
481195 0182
c
Notice to User: The MAP NUMBER shown below should be used
l!I when placing map orders; the COMMUNITY NUMBER shown
""'"""'"'" above should be used on· insurance application~ for the subject
community.
MAP NUMBER
48041COl82 C
EFFECTIVE DATE:
JULY 2, 1992
Federal Emergency Management Agency
-
-
LEGEND
SPECIAL FLOOD HAZARD AREAS INUNDATED
BY 100-YEAR FLOOD
ZONE A No base flood elevations determined.
ZONE AE Base flood elevations determined.
ZONE AH
ZONE AO
ZONE A99
ZONE V
Flood depths of 1 to 3 feet (usually areas of
ponding); base flood elevations determined.
Flood depths of 1 to 3 feet (usually sheet flow
on sloping t~rrain); average depths deter-
mined. For areas of alluvial fan flooding;
velocities also determined.
To be protected from 100-year flood by
Federal flood protection system under con-
struction; no base flood elevations deter-
mined.
Coastal flood with velocity hazard (wave
action); no base flood elevations determined.
ZONE VE Coastal flood with velocity hazard (wave
action); base flood elevations determined.
FLOODWAY AREAS IN ZONE AE
OTHER FLOOD AREAS
ZONE X A.reas of 500-year flood; areas of 100-year
flood with average depths of less than 1 foot or
with drainage areas less than 1 square mile;
and areas protected by levees from 100-year
flood.
OTHER AREAS
ZONE X Areas determined to be outside 500-year flood-
plain.
ZONED Areas in which flood hazards are undeter-
mined.
UNDEVELOPED COASTAL BARRIERS
Floodplain Boundary
Floodway Boundary
Zone D Boundary
. . Boundary Dividing Special Flood Hazard
Zones, and Boundary Dividing Areas of Dif-
ferent Coastal Base Flood Elevations Within
Special Flood Hazard Zones.
' ' . ·~ ~ \,
----513---
@-----@
(EL 987)
RM7x
•M1.5
Base Flood Elevation Line; Elevation in Feet•
Cross Section Line
Base Flood Elevation in Feet Where Uniform
Within Zone•
Elevation Reference Mark
River Mile
*Referenced to the National Geodetic Vertical Datum of 1929
NOTES
This map i; for use in administering the National Flood Insurance Program; it
does not necessarily identify all areas subject to flooding, particularly from local
drainage sources of small size, or all planimetric features outside Special Flood
Hazard Areas. The community map repository should be consulted for possible
updated flood hazard information prior to use of this map for property purchase
or construction purposes.
Coastal base flood elevations apply only landward ofO.O NGVD, and include the
effects of wave action; these elevations may also differ significantly from those
developed by the National Weather Service for hurricane evacuation planning.
Areas of special flood hazard (100-yearflood) include Zones A, AE, AH, AO, A99,
V, and VE.
Certain areas not in Special Flood Hazard Areas may be protected by flood
control structures.
Boundaries of the floodways were computed at cross sections and interpolated
between cross sections. The floodways were based on hydraulic considerations
with regard to requirements of the Federal Emergency Management Agency.
APPENDIXB
DETENTION BASIN SIZING BY TRIANGULAR HYDROGRAPHS
Job No. 2311-001
1) Detention Basin Drainage Area (acres) -
2) Peak Inflow Rate into Basin (cfs) -
3) Peak Release Rate from Basin (cfs) -
6.182lacres
53.65jcfs
18.11lcfs
4) Total Inflow Volume into Basin (acre-feet) -4.148975 acre-feet
V =Direct Runoff for 25-yr storm x Total Improved Area
V = Q (feet) x Drainage Area (acres)
Q = [P -(0 .2 x S)]2 =
P + (0.8 x S)
8.053656 inches
25-yr. Post-Developed
25-yr. Pre-Developed
P = 25-yr 24-hr Rainfall = ._I __ 8_._.8 I inches cs Drainage Manual (pg. 25)
S = 1000/CN -10 = 0.660981
CN = ..... l9_3_.8_~jSoil Type -Silty Sand, Lean Clay, Fat Clay
Soil Use -80% is Impervious (CN=98)
5) Available Storage Depth of Basin (feet) -
6) Required Freeboard in Basin (feet) -
7) Side Slopes of Basin (Horiz. I Vert.) -
8) Width of Maintenance Berm (feet) -
20% is Landscaped (CN=77)
.-----3 ..... lfeet
....__ __ o_.5_.lfeet
41 :1
....__ __ o_.lfeet
RESULTS FROM DETENTION BASIN SIZING PROGRAM, VERSION 1.4 BY DODSON & ASSOCIATES, INC.
Minimum Required Detention Volume 1.8 ac-ft
Add 10% Factor of Safety 0.18 ac-ft
MINIMUM REQUIRED DETENTION VOLUME 1.98 ac-ft
College Station Drainage Criteria Manual Detention Basin Calculations
Proiect: ALLSAFE STORAGE WELLBORN RD.
Job# 2311-001
System: BRAZOS COUNTY 25 YR STORM
By: HJH Date: 812V02
Rev: HJH Date: 10/29102
Chic by: WBP Date:
File Nam&: 2311-001 DRAINAGE CALCS
PRE-DEVELOPMENT
Area Site Area Runoff Time Cone. Intensity Runoff
Description (acres) "C2s" (min) "hs" 02s in cfs
To Basin 6.182 0.39 17.6 7.608 18.11
Note: •c• value based on Natural Grasslands wl 1% Slope (CS Drainage Polley, Table 111·1)
POST-DEVELOPMENT (ULTIMATE)
Area Site Area Runoff Time Cone. Intensity Runoff
Description (acres) "C2s" (min) "125" Qz5 in cfs
To Basin 6.182 0.88 10 9.861 53.65
Note: •c• value based on lmpervlOUs Areas and Landscaped Areas wl 1% Slope (CS Drama~• PolteY. Tabla /11-1)
DETENTION STORAGE vs. WATER SURFACE ELEVATION
Waler Surfece Area Area Detention Storeige Detention Storage
El eve.lion ls.f.l {eicres) le.I.\ Cumuletlve tecre-feetl
325.50 36,122 0.829 17638.71 2.791
325.00 34,432 0.790 32790.41 2.386
324.00 31,148 0.715 29570.91 1.633
323.00 27,993 0.643 26499.17 0.954
322.00 25,005 0.574 15066.00 0.346
321.00 5,127 0.118 2563.50 0.059
320.00 0.000
OUTFLOW CALCULATIONS 18 inch Orifice Dlscharae Pioe
Orifice Equation
TxDOT:
Equations: Intensity "I" : bl(Hd) •
b,,: 89
d25 : B.5
82, = 0.754
Peak Runoff "Q": C ,(CiA)
Cf: 1.10
(product of C~C) cen not be greater than 1.0)
Post-Development "CN" ·Area Draining to Detention Basin
Total Area=
Impervious Area =
Landscaped Area=
T otol Acres =
6.182 acres
4.95 acras
1.24 acras
6.182 acres
Avemge 'cN• = (•cN•, x Area, + •cN1 2 x Areo 2 + .... + •cN•; x Area;)
Total Aroo
Top of Berm is 325.50
25-year WSE is 325.00
Ave~ 'CN" : 93.8
98
77
Q : C x Ax (2 x g x h)' 0.5 Try using orifice w/ diameter= 18 Inches
Q = Peak OulOow Discharge (els)
C = Orifice Coefficient=
A = Cross-sectional Area of Orifice
g = Gre.vlte.llonel coemcienl =
h : Head on Onnce (fl.)
0.7 onnce Ftowtine =
Midpoint of orince :
32.2 ft./sec2 Maximum W.S.E. =
ToilweterW.S.E.:
320.00
320.75
325.00
322.00 (High Bank of Streom@ Pond Outlet)
Head on OriOce (h100in feet)= 3.00 QDIKll-.. = 17.19 cfs OK Allowable Discharge: 18.11
CONVEYANCE CALCULATIONS FOR BASIN DISCHAGE PIPE
Type of Pipe: RCP
Discharge Mannings Length Nominel Hydraulic Grade% Velocity Capacity
'rom Orifice Eqtn ·n· (fl.) Pipe Size Radius (fl.If!.) (fps) (els)
{els) llnl (f\)
17.19 0.013 52 36 0.8 0.00173 3.92 27.74
TIME OF CONCENTRATION
Sheetf/ow Shallow Concentrated Flow
Area Description Area Length P2 Slope Manning's Sheet Flow Length Slope Velocity
(acres) (ft.) (in.) (ft.lft.) "n" Time (hrs.) (ft.) (ft./ft.) (ft./sec.)
Pre-Development 6.182 100 4.5 0.015 0.15
Post-Development 6.182 300 4.5 0.01 0.011
1 Tc = Sheet Flow+ Shallow Concentrated Flow+ Ditch/ Pipe Flow
2 Sheet Flow: Tt = 0.007(nL)0·~/((P2)°"5s0.4)
Tt =Travel Time (hrs.)
0.15 320 0.0125
0.05 50 0.01
n =Manning's Roughness Coefficient (Short Prairie Grass (n=0.15) Concrete (n=0.011))
L = Flow Length
P2 = 2-year, 24-hour Rainfall (in.)
s =Slope of Hydraulic Grade Line (land slope ft./ft.)
Shallow Concentrated Flow: Tt = U(3600*V)
Tt =Travel Time (hrs.)
L = Flow Length
1.80
3.00
V = 16.1345*(s"0.5), (unpaved) Average Velocity (ft./sec., 210-Vl-TR-55, Second Ed., June 1986)
3600 = Conversion factor from hours to seconds
1 Source : Drainage Criteria Manual for Montgomery County, Texas
2Note : Equation good for distances 300 ft. and less
Cone. Flow
Time (hrs.)
0.05
0.00
Ditch/Pipe Flow
Length Slope Velocity K:;onc. F/ov.
(ft.) (ft.lft.) (ft.lsec.) Time (hrs.
640 0.0039 2.00 0.09
50 0.01 3.00 0.00
Total Time of
Concentration
(hrs.) (min)
0.29 17.6
0.06 3.5
Use
Tc
(min)
17.6
10
Project: Al/Safe Storaae 13101 Wellborn Road Equations:
Job# 2311-001 TXDOT Intensity"/"= b!(t c+d)•
System: BRAZOS COUNTY, 25 Yr. And 100 Yr. 25-Year Storm Event 100-Year Storm Event
By: H.J.H. Date: 8113/02 b = 89 b = 96
Rev: H.J.H. Date: 1lll29102 d = 8.5 d = 8.0
Chk by: Date: e -0.754 e -0.730
Peak Runoff "Q "= C ,(CA)
25-Year Storm Event 100-Year Storm Event
c, = 1.10 c, = 1.25 c = 0.90 c -0.90 /mJJ9rvious Areas c -0.40 c -0.40 Landsca/J9d Areas wl 1 % Slo/J9
The product of C, and C can not be greater than 1. 0
Notes: Minimum allowable Velocitv in Storm Sewers= 3.0 fcs
File Name: 2311-001 Drainaae Cales.xis Maximum allowable Velocitv in Storm Sewers = 15 fps
POST-DEVELOPMENT RUNOFF CALCULATIONS FOR CONVEYANCE SYSTEM DESIGN
Area Area Total Area Time Cone. Cumulative Cumulative Intensity Intensity Runoff Runoff Mannings Length Nominal Hydraulic Grade% Velocity Capacity
No. From To (acres) (acres) (min) -c.,,,· "C,oo" .,.,,,. .,100" "Q2~t "0100" •n• (ft.) Pipe Size Radius (ft./ft.) (fps) (cfs)
CirVhrl CirVhrl lcfsl (cfs) fin) (ft)
A1 1 2 0.544 0.544 10.00 0.90 1.00 9.9 11 .6 4.80 6.33 0.011 95 18 0.4 0.00300 3.85 6.80
A2 2 3 0.939 1.483 10.41 0.95 1.00 9.7 11.4 13.69 16.98 0.011 115 24 0.5 0.00374 5.20 16.35
A3 Type A 3 0.999 0.999 10.00 0.95 1.00 9.9 11.6 9.35 11.63 0.011 35 24 0.5 0.00200 3.81 11.96
A3 3 4 0.999 2.482 10.78 0.95 1.00 9.6 11.3 22.52 28.01 0.011 75 30 0.6 0.00467 6.75 33.13
A4 4 5 0.951 3.433 10.96 0.95 1.00 9.5 11.2 31.03 38.46 0.011 95 30 0.6 0.00516 7.09 34.82
A5 5 6 0.877 4.310 11.19 0.95 1.00 9.4 11.1 38.62 47.88 0.011 95 30 0.6 0.00516 7.09 34.82
AS 6 Basin 0.830 5.140 11.41 0.91 1.00 9.3 11.0 43.60 56.62 0.011 47 36 0.8 0.00532 8.13 57.49
Total Acreage to Ditch= 5.140 acres Total Q,. = 43.60
lOo-'fe_o..r ~~ ws~ (_~cl
SW ~ q Bv\\o0A.~ 1J ~ E
Channel Calculat or
Given Input Data:
Shape .......................... .
Solving for .................... .
Flowrate ....................... .
Slope .......................... .
Manning ' s n .................... .
Height ......................... .
Bottom width ................... .
Left slope ..................... .
Right slope .................... .
Computed Resul ts:
Depth .......................... .
Velocity ....................... .
Full Flowrate .................. .
Flow area ...................... .
Flow perimeter ................. .
Hydr aulic radius ............... .
Top width ...................... .
Area ........................... .
Peri meter ...................... .
Percent full ................... .
Dr~~(.(.jQ_ A~= o.~O/ tl..c.
Q= q.3~ cfs
Page 1
Trapezoidal
Depth of Flow
9.3900 cfs
0.0025 ft/ft
0.0130
1.0000 ft
0 .0000 ft
0.0500 ft/ft (V/H)
0.0500 ft/ft (V/H)
0.4660 ft
2.1623 fps
71.9494 cfs
4.3427 ft2
18.6624 ft
0.2327 ft
18.6391 ft
20.0000 ft2
40.0500 ft
46.5977 %
lbD-~ew-~ W~~ C~c. l\JW ~ of gv\\ol~ D ~ E 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 1.6100 cfs 0.0025 ft/ft 0.0130 1. 0000 ft 0.0000 ft 0.0200 ft/ft (V/H) 0.0200 ft/ft (V/H) 0.1705 ft 1.1071 fps 179.9993 cfs 1.4542 ft2 17.0577 ft 0.0853 ft 17.0543 ft 50.0000 ft2 100.0200 ft 17.0543 % \oo-yr. ~e~ BlOf:>· 'D f!=-= 3J (..3s '3~:5.11 (3\0j. (:: II>• 3:l.b. l0 L O.'J. 'f. f'F=3;;i b. 35 -::---~----...e!--...J 0r'4..l~e. ~ ::-0. I 3'8 ttc Q= I.bl cfs l FU=·3d5.(H @O.;).S'/-Page 1 TP :-3.;l~. IC)
APPENDIXC
See Full-Size Plans Attached
C-4 Site Grading and Paving Plan
C-5 Drainage Area Map and Drainage Plan
C-6 Drainage Calculations
C-14A Details
C-14 B Details