HomeMy WebLinkAboutDrainage ReportCERTIFICATION
I, Joseph P. Schultz, Licensed Professional Engineer No. 65889, State of Texas, certify that this report
for the drainage design for the Aggieland Fitness Center in College Station, Texas, 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 required for
this project since the site discharges directly into an ex isting drainage and immediately into the 100-
year floodplain limits.
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TABLE OF CONTENTS
AGGIELAND FITNESS CENTER
CERTIFICATION ................................................................................................................................................................. 1
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 .............................................................................................................. 3
STORM SEWER CULVERT DESIGN ............................................................................................................................... 4
STORM RUNOFF DESIGN CALCULATIONS ................................................................................................................. 4
CONCLUSIONS ..................................................................................................................................................................... 5
APPENDIX A ......................................................................................................................................................................... 6
Calculatio11s
EXHIBIT A ........................................................................................................................................................................... 16
Drainage Area Map
LIST OF TABLES
TABLE 1 -Rainfall Intensity & Runoff Data .......................................................................................... 3
TABLE 2 -Time of Concentration (tc) Equations .................................................................................. 4
2
DRAINAGE REPORT
AGGIELAND FITNESS CENTER
INTRODUCTION
The purpose of this report is to provide the hydrological effects of the construction of the
dome-structure building and parking area, and to show that the stom1 water runoff wi 11 be
controlled in such a manner so as to have minimal offsite or downstream impact.
GENERAL LOCATION AND DESCRIPTION
The project is located on 2.27 acres out of a 4.02-acre tract located in College Station, Texas.
Most of the site is open land with grass. A 0.477 acre portion on the northwest end along the
North Fork of Lick Creek is being dedicated as greenway. This area is primarily wooded. The
existing ground elevations range from elevation 280 to elevation 292. 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 Lick Creek Drainage Basin. The site is located in a Zone X
Area according to the Flood Insurance Rate Map (FIRM) prepared by the Federal Emergency
Management Agency for Brazos County, Texas and incorporated areas dated February 9, 2000,
panel number 48041C0201 D. Zone X Areas are determined to be outside of the 500-yr
floodplain. This site is not within the limit of study for the FIRM. However, the approximate
100-year floodplain limits were previously determined by the City of College Station, and these
limits were included on the Final Plat for the project. This floodplain area is also shown on
Exhibit A. Most of the floodplain area for this tract is located in the Greenways Dedication
Area.
DEVELOPMENT DRAINAGE PATTERNS
The storm water runoff from the site flows north into the State Highway 6 right-of-way or
directly into the North Fork of Lick Creek. A majority of the runoff from the developed area
will be diverted so that it enters the creek and the 100-year floodplain rather than the right-of-
way; therefore, no detention is required for this project. The drainage area boundaries are
shown on Exhibit A.
DRAINAGE DESIGN CRITERIA
The design parameters for the storm sewer are as follows:
• The Rational Method is utilized to determine peak storm water runoff rates for the
storm sewer design.
• Design Storm Frequency
Storm culverts
Curb openings
3
25-year storm event
10 and 100-year storm events
• Runoff Coefficients
Grass and wooded areas
Commercial areas
Impervious surfaces
c = 0.30
c = 0.75
c = 0.90
• Rainfall Intensity equations and values for Brazos County can be fo und in Table 1.
• Time of Concentration, tc -Calculations fo r are based on the method found in the TR-
55 publication. Refer to Appendix A for th e equations and calculati ons. The drainage
runoff flow paths used for calculating the times of concentration for each drainage are
shown in Exhibit A.
STORM WATER RUNOFF DETERMINATION
The peak runoff values were determined in accordance with the criteria presented in the
previous section for the 10 and 100-year storm events. The runoff coefficients are based
on the development of this tract. The drainage areas are shown in Exhibit A. Runoff
conditions are summarized in Table 1. The time of concentration equations are shown in
Table 2.
TABLE 1 -Rainfall Intensity & Runoff Data
Area c 5 year storm 10 year storm 25 year storm 50 year storm le Area
# (acres)
A1 A2 Al Total
1 0.63 1.52 2.75 4.90 ----------2 1.36 0.84 0.00 2.20
The Rational Method:
Q=CIA
Q = Flow (cfs)
A= Area (acres)
C = Runoff Coeff.
I = Rainfall Intensity (in/hr)
Brazos County:
511:ear storm 10 11:ear storm
b = 76 b = 80
d = 8.5 d = 8.5
e = 0.79 e = 0.76
C1 C2 C3 Crotal Is
(min) (in/hr)
0.9 0.75 0.3 0.52 24.2 4.92 ------------0.9 0.75 0.3 0.84 11.2 7.32
I = b I (tc+d)e
le = Time of concentration (min)
le = L/(V*60)
L = Length (ft
V =Velocity (ft/sec)
511:ear storm
b = 89
d = 8.5
e = 0.75
50 11:ear storm
b = 98
d = 8.5
e = 0.745
Os
(cfs)
12.46 --13.58
110 0 10 l2s
(in/hr) (cfs) (in/hr)
5.59 14.16 6.42 ------8.23 15.26 9.41
100 11:ear storm
b = 96
d = 8.0
e = 0.730
0 2s
(cfs)
16.25 --17.44
(Data taken from State Department of Hiqhwa11:s and Public Transportation H11:draulic Manual. page 2-16)
TABLE 2 -Time of Concentration (tc) Equations
lso
(in/hr)
7.29 --10.64
The time of concentration was determ ined using methods found in TR-55, "Urban
Hydrology f or Small Watersheds." The equations are as follows:
Time of Concentration:
4
T c= T t(sheet flow)+ Tt(concentrated sheet flow)
where: T1 =Travel Time, minutes
Oso
(cfs)
18.47 --19.72
100 year storm
1100 0 100
(in/hr) (cfs)
7.61 19.28 -----11.10 20.59
For Sheet Flow:
For Shallow Concentrated Flow:
where: Ti = 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
T1 =LI (60*V)
where: Ti = travel time, minutes
V =Velocity, fps (See Fig 3-1 , App. E)
L = flow length, feet
Refer to Appendix A for calculations.
STORM SEWER CULVERT DESIGN
A storm sewer culvert is proposed at the driveway for this development. This culvert will
be designed for the 25-year stonn event, and it will also pass the 100-year stom1 event
without overtopping the driveway. Refer to Appendix A for the culvert calculator data
sheets for the 25-and 100-year stonn events.
STORM RUNOFF DESIGN CALCULATIONS
As previously stated, the stom1 water runoff from this site will flow directly into the North
Fork of Lick Creek. The runoff from this site will increase due to the building and parking
lot construction. The parking lot will have a curb opening to allow the runoff to exit the
pavement area. A maximum depth of 1 O" for the 100-year storm event was selected to si ze
the openings. The following calculations will show that the depth of the water at the curb
opening does not exceed 10 inches for the 100-year storm event.
Capacity of curb openings solving Weir Flow Equation:
Q = 3* L * y312
Where: Q = flow at inlet, cfs
L = length of inlet opening, feet
y = total depth of flow on inlet, feet
For 1-3.5' opening flowing -4" deep (y=0.333 '), Q=2.02 cfs
5" deep (y=0.417'), Q=2.83 cfs
6" deep (y = 0.500'), Q = 3.71 cfs
7" deep (y = 0.583 '), Q = 4.67 cfs
7.5" deep (y = 0.625 '), Q = 5.19 cfs
8" deep (y = 0.667'), Q = 5.72 cfs
8.5" deep (y = 0.708 '), Q = 6.26 cfs
9" deep (y = 0.750'), Q = 6.82 cfs
For 1-2' divider with water flowing over it's top -
l" deep (y = 0.083 '), Q = 0.14 cfs
1.5" deep (y = 0.125 '), Q = 0.27 cfs
5
2" deep (y = 0.167'), Q = 0.41 cfs
2.5" deep (y = 0.208'), Q = 0.57 cfs
3" deep (y = 0.250'), Q = 0.75 cfs
4" deep (y = 0.33 3 '), Q = 1.15 cfs
For Curb Opening: [3-3.5 ' openings with 2-2' dividers]
Total flow going thru Curb Opening -Q10 = 15.26 cfs
Q100 = 20.59 cfs
Determine depth of flow for Q10 by trial and error:
For 8" deep: (3 openings* 5.72 cfs/opening) + (2 dividers* 0.41cfs)=17.98 cfs
17.98 > 15.26 =>flows less than 8" deep
For 7" deep: (3 * 4.67 cfs) + (2 * 0.14 cfs) = 14.29 cfs
14.29 < 15 .26 => flows deeper than 7"
For 7.5" deep: (3 * 5.19 cfs) + (2 * 0.27 cfs) = 16.11 cfs
16.11 > 15 .26 =>flows less than 7.5" deep
For Q10, the flow thru the Curb Opening is between 7" and 7.5" deep.
Determine depth of flow for Q100 by trial and error:
For 8.5'' deep: (3 openings* 6.26 cfs/opening) + (2 dividers * 0.57 cfs) = 19.92 cfs
19.92 < 20.59 =>flows deeper than 8.5"
For 9" deep : (3 * 6.82 cfs) + (2 * 0.75 cfs) = 21.96 cfs
21.96 > 20.59 =>flows less than 9" deep
For Q100, the flow thru the Curb Opening is between 8.5" and 9" deep.
CONCLUSIONS
The construction of this project will increase the storm water runoff from this site. However,
the runoff will be carried through the parking area to an existing drainage and immediately
into the 100-year floodplain. The increased flow in this tributary should 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.
6
APPENDIX A
Calculations
7
Proposed 27n Culvert -25 Year Storm
Culvert Calculator
Entered Data:
Shape ........... .
Number of Barrels
Solving for ....... .
Chart Number ...... .
Scale Number ..... .
Chart Description
Scale Description
Overt opping .. .
Flowrate ........ .
Manning 's n ................. .
Roadway Elevation .............. .
Inlet Elevation ................ .
Outlet Elevation ............... .
Diameter ................... .
Length ................... .
Entrance Loss
Tailwater ....
Computed Results:
Headwater ................. .
Slope ... · .................. .
Velocity .................. .
Circular
1
Headwater
1
3
CONCRETE PIPE CULVERT; NO BEVELED RING ENTRANCE
GROOVE END ENTRANCE, PIPE PROJECTING FROM FILL
Off
16.2500 cfs
0. 0140
284.0000 ft
281.2700 ft
281.0000 f t
27 .0000 in
54.0000 ft
0.0000
2.2500 ft
283.6812 ft Outlet Control
0.0050 ft/ft
4.0869 fps
Proposed 2 7n Culvert -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 Elevat ion .............. .
Inlet Elevation ........... .
Ou t l et Elevation .
Diameter ........ .
Length . . . . . . .... .
Entrance Loss ........... .
Tailwater ............... .
Computed Results:
Headwater .............. .
Slope . . . . . . . . . ..... .
Veloc ity .................... .
Aggieland Fitness Center
College Station, Texas
Circular
1
Headwater
1
3
CONCRETE PIPE CULVERT; NO BEVELED RING ENTRANCE
GROOVE END ENTRANCE, PIPE PROJECTING FROM FILL
Off
19.2800 cfs
0. 0140
284 .0000 ft
281 .2700 ft
281.0000 ft
27.0000 in
54.0000 ft
0.0000
2.2500 ft
283.8569 ft Outlet Control
0.0050 ft/ft
4.8490 fps
Time of Concentration Calculations
Drainage Area #1
Sheet Flow: Flow length = 185' = L
Slope = 1.1 %
n = 0.15, sho1i grass prairie
P2 = 4.5"
T1=0.007 (0.15 * 185 )0 8
(4.5)05 (0.011)04
= 0.286 hours = 17.2 minutes
Shallow Co ncentrated Flow: Flow length = 295 ' = L
Slope = 1.2%
Flow through Ditch #1:
For unpaved surface at 1.2%, Velocity (V) = 1.7 fps (see Fig. 3-1 )
= 295 ' I (60*1.7) = 2.9 minutes
(Refer to attached channel calculations)
V-bottom ditch with 1 :4 sides, Flow length = 167' = L
Slope = 0.76%
(Note: slope & length obtained from old plans.)
n = 0.035
Area, A = approximately 1 acre
Qs = 3.9 cfs (using tc = 20.1minutes,C=0.75)
From Manning's data, Velocity, V = 1.8 fps
t1 = 92.8 sec = 1.5 minutes
Flow through existing 24 " RCP:
Flow through Ditch #2:
(Refer to attached culvert calculations)
24" RCP, Flow length= 90 ' = L
Slope = 0.5%
n = 0.014
Area, A = approximately 2 acres
Q5 = 7.8 cfs (using tc = 22.2 minutes, C = 0.75)
From Manning's data, Velocity, V = 2.5 fps
t1 = 36.0 sec= 0.6 minutes
(Refer to attached channel calculations)
V-bottom ditch with 1:5 sides, Flow length = 260 ' = L
Slope = 0.72%
(Note: slope & length obtained from old plans.)
n = 0.035
Area, A = approximately 3 acres
Q5 = 11.1 cfs (using tc = 24.2 minutes, C = 0.75)
From Manning's data, Velocity, V = 2.2 fps
t1 = 11 8.0 sec= 2.0 minutes
Tc= 17.2+2.9+ 1.5+0.6+2.0 = 24.2 minutes
Sheet Flow:
Time of Concentration Calculations
Drainage Area #2
Flow length = 100' = L
Slope = 2%
n = 0.15, short grass prairie
P2 = 4.5 "
T1 = 0.00 7 (0.15 * 100)08
(4.5)05 (0.02)04
= 0.138 hours = 8.3 minutes
Flow along Pavement Segment #1:
Flow length= 178 ' = L
Slope = 3%
For paved surface at 3%, Velocity V =3.5 fps (see Fig. 3-1)
= 178' I (60*3.5) = 0.8 minutes
Flow along Pavement Segment #2:
Flow length= 270' = L
Slope = 1.1%
For paved surface at 1.1 %, Velocity V =2.15 fps (Fig 3-1)
~ = 270' I (60*2.15) = 2.1 minutes
Tc= 8.3 + 0.8 + 2.1 = 11.2 minutes
Data for Drainage Area #1 Tc Calculations
Flow Path Area
Segment
(acres)
Ditch #1 1
Exist. 24" RCP 2
Ditch #2 3
The Rational Method:
Q =CIA
Q = Flow (cfs)
A= Area (acres)
C = Runoff Coeff.
I = Rainfall Intensity (in/hr)
Brazos County:
5 year storm
b = 76
d = 8.5
e = 0.785
c
0.75
0.75
0.75
tc 5 year storm
Is Os
(min) (in/hr) (cfs)
21 .6 5.250 3.94 -
22.2 5.169 7.75
24.2 4.919 11 .07
I = b I (tc+d)"
tc = Time of concentration (min)
tc = L/(V*GO)
L = Length (ft
V =Velocity (ft/sec)
.µ .._ -.µ .._
C1J a.
0 .-
VI
C1J
VI s... :::s
0 u s... cu .µ
"' ::x
3-2
.50
.20 -
.10
.06
.04
.02 -
.01 -
.005 I
1
j
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J
I
I
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'
J
Q
:,,,Q, l~ ~' ~ .:,., ~~ q_~I
I
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I
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Average velocity, ft/sec
...
l.J
. . . .
J , ,
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10
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Fi1eutt :J-1.-Av~ralC~ v~lociti~s for cstimalinJC trnv~I tim~ for <hallow conc~nlrat~d now.
(210-Vl-TR-55. Second Ed., June 1986)
I
20
Ditch #1 -5 Year Storm
Time of Concentration Calculatio n s
Channel Calculator
Given Input Data:
Sh ape .......................... .
Solving for .................... .
Flowrate ....................... .
Slope .......................... .
Manning ' s n .................... .
He ight ......................... .
Bottom width ................... .
Left slope ..................... .
Right slope .................... .
Computed Results :
Depth .......................... .
Velocit y ....................... .
Full Flowrate .................. .
Flow area ...................... .
Flow perimeter ................. .
Hydraulic radius ............... .
Top width ...................... .
Area ........................... .
Perimeter ...................... .
Percent full ................... .
~ggieland Fitness Center
College Station, Texas
Trapezoidal
Depth of Flow
3.9000 cfs
0.0076 ft/ft
0 .0350
20.0000 in
0.0000 in
0 .250 0 ft /ft (V/H)
0.2500 ft/ft (V/H)
8.7191 in
1.8468 fps
35.6904 cfs
2.1118 ft2
71 .8997 in
4.2294 in
69.7529 in
11.1111 ft2
164.9242 in
43.5956 %
Existing 24" Pipe -5 Year Storm
Time of Concentration Calculations
Culvert Calculator
Entered Data:
Shape ...................... .
Number of Barrels . . ..... .
Solving for ............... .
Chart Number .............. .
Scale Number .......... .
Chart Description
Scale Description
Overtopping ................ .
Flowrat e .......... .
Manning 's n ...... .
Roadway Elevation ..
Inlet Elevation ....
Outlet Elevation ........ .
Diameter ................ .
Length ..................... .
Entrance Loss .. .
Tailwater ..... .
Computed Results:
Headwater ...... .
Slope ............ .
Velocity .......... .
Aggie l a nd Fitne s s Center
Coll e g e Sta t ion , Texa s
Circular
1
Headwater
1
3
CONCRETE PIPE CULVERT; NO BEVELED RING ENTRANCE
GROOVE END ENTRANCE, PIPE PROJECTING FROM FILL
Off
7.8000 cfs
0.0140
288.0000 ft
283.7300 ft
283.2800 ft
24.0000 in
90.0000 ft
0.0000
2.0000 ft
285.4993 ft Outlet Control
0.0050 ft/ft
2.4828 fps
Ditch #2 -5 Year Storm
Time of Concent ration Calculations
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 radiu s ............... .
Top width ...................... .
Area ........................... .
Perimeter ...................... .
Percent full ................... .
Aggieland Fitness Center
Col lege Statio n, Texas
Trapezoidal
Depth of Flow
11.1000 cfs
0.0072 ft/ft
0.0350
20.0000 in
0.0000 in
0.2000 ft/ft (V/H)
0.2000 ft/ft (V/H)
11.9597 in
2 .2350 fps
43.7340 cfs
4.9664 ft2
121.9651 in
5.8637 in
119.5966 in
13.8889 ft2
203.9608 i n
59.7983 %
EXHIBIT A
Drainage Area Map
16