HomeMy WebLinkAbout18 North Forest Subdivision 03-89...
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Drainage Report
for
North Forest Subdiv ision
College Station , Tex as
November 2003
R EVISED D ecember 2 003
Developer:
North Forest, LLC
420 Tanow Street
College Station, Texas 77840
Prepared Bv:
TEXC ON General Contractors
1707 Graham R oad
College Station , Texas 77845
(979) 764-7743
CERTIFICATION
I, Joseph P . Schultz, Licensed Professional Engineer No. 65889, State of Texas , certify that this
revised report for the drainage design for the North Forest Subdivision 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 storm water runoff detention is not
being required for this project since the site discharges directly into an existing drainage and
immediately into the 100-year floodplain limits .
TABLE OF CONTENTS
NORTH FOREST SUBDIVISION -REVISED 1212003
CERTIFICATION .................................................................................................................................................................. 1
TABLE OF CONTENTS ........................................................................................................................................................ 2
LIST OF TABLES .................................................................................................................................................................. 2
INTRODUCTION ................................................................................................................................................................... 3
GENERAL LOCATION AND DESCRIPTION .................................................................................................................. 3
FLOOD HAZARD INFORMATION .................................................................................................................................... 3
DEVELOPMENT DRAINAGE P ATTERNS ....................................................................................................................... 3
DRAINAGE DESIGN CRITERIA ..................................................... , .................................................................................. 4
STORM WATER RUNOFF DETERMINATION ............................................................................................................... 5
STORM SEWER DESIGN .................................................................................................................................................... 6
CONCLUSIONS ..................................................................................................................................................................... 7
APPENDIX A .......................................................................................................................................................................... 8
Time of Concentration Equations & Calculations
APPENDIX B ........................................................................................................................................................................ 12
Storm Inlet Design Data & Calculation s
APPENDIX C ........................................................................................................................................................................ 15
Storm Pipe Design Data & Calculations
EXHIBIT A ............................................................................................................................................................................ 26
Pre-Development Drainage Area Map
EXHIBIT B ............................................................................................................................................................................ 28
Post-Development Drainage Area Map
LIST OF TABLES
TABLE 1 -Rainfall Intensity & Runoff Data .......................................................................................... 4
TABLE 2 -Time of Concentration (tc ) Equations .................................................................................. 4
TABLE 3 -Pre-Development Drainage Data .......................................................................................... 5
TABLE 4 -Post-Development Drainage Data ......................... : .............................................................. 5
TABLE 5 -Pre-vs. Post-Development Drainage Data ........................................................................... 6
DRAINAGE REPORT
NORTH FOREST SUBDIVISION -RE VISED 1212003
INTRODUCTION
The purpose of this revised report is to provide th e hydrological effects of the construction of
the North Forest Subdivision , and to show that the storm water runoff will be controlled in such
a manner so as to have minimal offsite or downstream impact. This report does not address the
future development of Lot 1, Block 1 of the subdivision. This lot is zoned A-P and the
drainage from this lot will need to be addressed at the time of it's development.
GENERAL LOCATION AND DESCRIPTION
The project is located on a 20 .8 acre tract located in College Station, Texas . Most of the site is
open land with grass . Approximately 2.4 acres on the southwest end along Bee Creek are being
dedicated as greenway. This area is partially wooded. The existing ground elevations range
from elevation 238 to elevation 260 . 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 Bee Creek Drainage Basin. A portion of the site is located in a
Special Flood Hazard 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 48041C0163-D . Three of these Special Flood Hazard
Areas are located on the property. Flood Zone AE areas are inundated by the 100-year flood
with base flood elevations determined. Flood Zone X Shaded are areas of the 500-year flood
and areas of the 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 the 100-year flood. Flood Zone X
Unshaded areas are determined to be outside of the 500-yr floodplain . These floodplain areas
are shown on Exhibit A. All of the 100-year floodplain area for this tract is located within the
Greenways Dedication Area.
DEVELOPMENT DRAINAGE PATTERNS
A portion of the pre-development storm water runoff from the site flows southeast directly into
the 100-year floodplain and Bee Creek, w hile the majority of the runoff from the pre-
development area flows to the east onto the adjacent property, and then into the 100-year
floodplain. As shown on Exhibit A, the pre-development runoff is divided into 3 areas which
flow onto the adjacent property. Also, a portion of the site flows into North Forest Parkway.
After development, these conditions will be changed such that only a small portion of the
developed area will continue to flow onto the adjacent prop e rty , and the majority of th e runoff
wi ll be captured by the stom1 sewer system and discharged directly into Bee Creek. Because of
these conditions no dete n · · re uire d for thi s development. The pre-d eve lopm e nt drainage
area oundaries are shown on Exhibit A, and th e post-dev e lopment drainage area bound a ri es
a re shown on Ex hibit B.
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 sewer system
• Runoff Coefficients
Single Family Residential
Undeveloped
10 and 100-year storm events
c = 0.55
c = 0.30
• Rainfall Intensity equations and values for Brazos County can be found in Table l .
• 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 paths used for calculating the pre-development times of concentration are
shown in Exhibit A, and the flow paths used for the post-development tim es of
concentration are found in Exhibit B. For smaller drainage areas, a minimum tc of 10
minutes is used to determine the rainfall intensity values .
TABLE I -Rainfall Intensity & Runoff Data
Rainfall Intensity Values
(in/hr)
Storm tc =
Event 10 min
Is 7.693
110 8.635
l2s 9.861
lso 11 .148
1100 11 .639
Brazos
County:
5 'i_ear storm 10 'i_ear storm
b= 76 b= 80
d= 8.5 d= 8 .5
e= 0.785 e= 0 .763
I = b I (tc+d)"
I = Rainfall Intensi ty (in/hr)
tc = U(V*60)
le= Time of concentration (min)
L = Length (ft)
V =Velocity (ft/sec)
25 'i.ear storm 50 'i_ear storm 100 'i_ear storm
b= 89 b= 98 b= 96
d= 8 .5 d= 8 .5 d= 8.0
e= 0 .754 e= 0 .745 e= 0 .730
(Data taken from State Department of Highways and Public Transportation H'i,draulic Manual, pag e 2-16)
TABLE 2 -Time of Concentration (tc ) Equations
The tim e of co ncentration was de termin ed us in g me th ods fo und in TR-55, ··Urb a n
Hy drology.for S 111al/ Wat e rsh eds. " Th e equations are as.follo ws:
Time of C on centration: Tc = Tf(s hcrl llon) + T((co11re11fr;1ft•tl s htl'I ll o")
w here: T 1 =Tra ve l Tim e , minute s
For Sheet Flow :
where: T 1 = travel time , hours
n =Manning 's roughness co effi c ient
L = flo w length , feet
P2 = 2-y ear, 24-hour rainfall = 4.5 "
s = land slope , ft/ft
For Shallow C oncentrated Flow: T 1 =LI (60*V)
Refer to Appendix A for calculations .
STORM WATER RUNOFF DETERMINATION
where : T 1 = travel time , minutes
V =Velocity, fps (S e e Fig 3 -1, App . E )
L = flow length, feet
The peak runoff values were determined in accordance with the criteria presented in the
previous section for the 5 , 10 , 25, 50, and 100-year storm events . Pre-development
drainage area data is summarized in Table 3 . The runoff coefficients for post-dev e lopment
calculations are based on the future development of this tract , and the peak runoff values
determined for the post-development condition are shown in Table 4 .
TABLE 3 -Pre-Development Drainage Data
Area c 5 year storm 10 year storm 25 year storm 50 year storm 100 year storm tc Area# (acres)
C2 CTot•I Is Os 110 o,o l2s 02s lso Oso 1, .. o, ..
A,_
C1
A, Total (min) (i n/hr) (cfs) (In/hr) (cfs) (in/hr) (cfs) (in/hr) (cfs) (in/hr) (cfs)
Pre-devel
1 9 .36 0 9 .36 0 .30 0 0 .30 40.2 3.598 10.10 4 .126 11.59 4.753 13.35 5.420 15 .22 5 .671 15 .92
2 1.64 0 1.64 0 .30 0 0.30 30.7 4 .267 2 .10 4 .869 2.40 5.598 2 .75 6 .371 3.13 6 .656 3.27
3 1.89 0 1.89 0.30 0 0 .30 29.0 4.418 2.50 5 .036 2 .86 5.789 3.28 6 .585 3 .73 6 .878 3.90
4 1.32 0 1.32 0 .30 0 0 .30 10 7.693 3 .05 8 .635 3.42 9.861 3.91 11.148 4.41 11.639 4.61
TABLE 4-Post-Development Drainage Data
Area c 5 year storm 1 O year storm 25 year storm 50 year storm 100 year storm
Area# (acres) tc
Is Os 110 o,o l2s 02s lso Oso 1, .. o, .. C1 C2 CTotol
A1 A,_ Total (min) (in/hr) (cfs) (in/hr) (cfs) (in/hr) (cfs) (in/hr) (cfs) (in/hr) (cfs)
101 1.37 0 1.37 0 .55 0 .3 0 .55 11.5 7.236 5.45 8 .136 6.13 9 .299 7 .01 10 .519 7.93 10.979 8 .27
102 1.56 0 1.56 0 .55 0 .3 0 .55 10 7.693 6 .60 8 .635 7.41 9 .861 8 .46 11 .148 9.56 11 .6 39 9.99
103 1.54 0 1.54 0 .55 0 .3 0 .55 10 7.693 6 .52 8 .635 7.31 9 .861 8.35 11 .148 9.44 11.6 39 9 .86
104 2 .07 0 2.07 0.55 0 .3 0 .55 17 .2 5.943 6 .77 6 .7 19 7.65 7.697 8.76 8 .726 9.9 3 9 .104 10 .3 7
105 1.8 2 0 1.82 0 .55 0 .3 0 .55 10 7.693 7.70 8 .635 8.64 9 .861 9 .87 1 1.148 11.1 6 11 .6 39 11.6 5
106 1.53 0 1.53 0 .55 0 .3 0 .55 10 7.693 6 .4 7 8 .6 35 7.27 9.861 8 .30 1 1.148 9 .38 11 .6 39 9 .79
107 0.54 0 0 .54 0 .55 0 .3 0 .55 10 7.693 2.28 8 .635 2.56 9 .86 1 2 .93 11 .148 3.3 1 11.6 39 3.4 6
108 0 .34 0.10 0.44 0 .30 0 .55 0 .36 10 7.693 1.2 1 8 .6 35 1.36 9.86 1 1.55 11 .148 1.75 11.639 1.83
109 0.42 0 .26 0.68 0 .30 0 .55 0.40 10 7.69 3 2.0 7 8 .635 2.32 9.86 1 2 .65 11.1 48 3.00 11 .639 3.13
11 0 1.3 1 0.68 1.99 0 .30 0 .55 0 .39 52 .0 3035 2.33 3.496 2.68 4 .036 3.10 4 .6 11 3.54 4.833 3.71
111 0 .00 0 .6 7 0.67 0 .30 0 .55 0.55 10 7.693 2.83 8.635 3.18 9 .86 1 3 .63 11 .148 4 .11 11.6 39 429
v
j
j
J
J
----___________ ___,.
TABLE 5 -Pre-vs. Post-Development Drainage Data
5 year storm 10 year storm 25 year storm 50 year storm 100 year storm
Pre/Post Area # Os 010 0 2s Oso 0100
(cfs) (cfs) (cfs) (cfs) (cfs)
Pre 1 10 .10 11.59 13 .35 15.22 15 .92
Post 108 1.21 1.36 1.55 1.75 1.83
Reduction in Flow : 8.90 10 .23 11 .80 13 .47 14.10
Pre 2 2 .10 2.40 2 .75 3.13 3 .27
Post109 2 .07 2.32 2.65 3 .00 3 .13
Reduction in Flow: 0 .03 0.07 0.10 0.14 0 .14
Pre 3 2.50 2.86 3 .28 3.73 3 .90
Post 110 2 .33 2 .6 8 3 .10 3.54 3 .71
Reduction in Flow: 0.18 0.17 0.19 0.20 0 .19
Pre 4 3 .05 3.42 3 .91 4.41 4.61
Post 111 2 .83 3.18 3 .63 4 .11 4 .29
Reduction in Flow: 0.21 0 .24 0 .27 0 .31 0.32
The pre-development drainage areas are shown on Exhibit A, and post-developme nt areas
are shown on Exhibit B. Even though the runoff coefficient for the developed conditions
increases the runoff, the storm sewer system diverts a majority of the runoff di rec tly to Bee
Creek, thereby reducing flow onto the adjacent property. Table 5 compares th e peak
runoff values for each of these conditions , verifying that the post-development offsite flow
onto the adjacent property is less than the pre-development offsite flow . The Greenway
Dedication Area discharges directly into Bee Creek for both pre-and post-deve lopment.
Since this area is not b eing developed , it is not being analyzed for this report. Lot 1, Block
1 is also unchanged for this developm ent. Upon its development in the future , it wi ll be
analyzed under a separate report .
STORM SEWER DESIGN
The storm sewer piping for this project has been selected to be Reinforced Concrete Pipe
(RCP) meeting the requirements of ASTM C-76 , Class III pipe and pre-cast Box Sections
meeting the requirements of ASTM C-789. The curb in lets will be cast-in-plac e concrete.
Appendix B presents a summary of the storm sewer inlet design parameters and
calculations . The inlets were designed based on a 10-year design storm . As per Co ll ege
Station guidelines, the capacities of inl ets in sump were reduced by 10 % to allow for
clogging.
Inlets were located to maintain a gutter flow depth of 5" or less, which wi ll prevent the
spread of water from reaching th e crown of th e road for the 10-year storm event. Refer to
Appendix B for a summary of the gutter flow depths at various locations . The runoff
intercepted by the proposed storm sewer inlets was calcu lated usin g th e following
equation s. The depth of flow in th e gutter was detennined by using th e Straight Crown
F low equ ation. The flows intercepted by Inl ets 2 , 3, 4, & 5 were calculated by using th e
Capac it y ofl nl ets On Grade equat io n . The cap acities for the in lets in s ump (Inl e ts I & 6 )
were calculated usin g the Inl ets in S um ps , Weir F low equ atio n with a maximum a ll ow a bl e
dep th of 7" (5" g utt e r flow plus 2" g utt e r depres s io n). These equations and th e resultin g
data a re summari zed in App endix B. Th e area be tw een th e ri g ht -of-w ay a nd th e curb lin e
o f the stree ts wi ll be fill ed as nec es sa ry to provid e a minimum of 6" of fr ee boa rd ab ove th e
curb line. This will ensure that the runoff from th e 100-year storm eve nt will remain
w ithin the street right-of-way.
Appendix C presents a summary of the storm sewer pipe desi gn parameters and
calculations . All pipes are 18" in diamet er or larger. For pip es with 18 " and 24"
diameters , the cross -sec tional area is reduced by 25%, as per College Station requirements.
A summary of how this was ac hieved is shown in Appendix Caswell. The pip es for the
storm sewer system were designed based on the 10 -year stom1 event; howev er, a ll will a lso
pass the 100-year storm event without any headw ate r . As req uired by College Station , th e
ve locity of flow in th e storm sewer pipe system is not low er than 2.5 feet pe r seco nd , and it
does not exceed 15 feet per second . As the data shows, even during low flow co n di lion s,
the velocity in the pipes and boxes will exceed 2.5 feet per second and prev ent sedim e nt
build-up in the pipes and boxes . The maximum flo w in the storm sewer pipe system wi ll
occur in Box 1. Appendix C contains a summary of the Manning pipe calculations as well
as flow diagrams mapping the flows through the storm sewer system for the 10 a nd I 00-
year events . The maximum velocity for the pipe system will be 6.6 feet pe r second a nd
will occur in Box I .
CONCLUSIONS
The construction of this project will increase the storm water runoff from this site .
However, a majority of the runoff will be carried through a storm sewer system directly to
Bee Creek and immediately into the 100-year floodplain . As noted previously , the po st-
development runoff that flows onto the adjacent property is less than the pre-deve lopm ent
runoff for each area . The increased flow directly into Bee Creek will not hav e a s ig ni ti cant
impact on the surrounding property . No flood damage to downstream or adjacent
landowners is expected as a result of this developm ent.
7
APPENDIX A
Time of Concentration Equations & Calculations
Pre-Development
Time of Concentration Calculations
Refer to Exhibit A for flow paths us ed for calcu lat ions.
Pre-Development Drainage Area 1:
Sh eet Flow: Flow length = 300' = L
Slope = 1.36%
n = 0.24, den se grass
P2 = 4 .5"
t, = 0 .007 (0.24 * 300)°-8
( 4 .5)05 (0.0136)0.4
t1 = 0.564 hours= 33.8 minutes
Shallow Concentrated Flow: Flow length = 790' = L
Slope = 1.6%
For unpaved s urface at 1.6%, Velocity (V) = 2.05 fp s (see Fi g. 3-1)
t1 = 790' I (60*2.05) = 6.4 minutes
Tc= 33.8 + 6.4 = 40.2 minutes
Pre-Development Drainage Area 2:
Sheet Flow: Flow length= 300' = L
Slope = 2.0%
t1 = 0.483 hours = 29.0 minutes
Shallow Concentrated Flow: Flow length = 275' = L
Slope= 2.8%
For unpaved surface at 2.8%, Velocity (V) = 2. 7 fps (see Fig. 3-1)
t1 = 275' I (60*2.7) = 1.7 minutes
Tc= 29.0 + 1.7 = 30.7 minutes
Pre-Development Draillage Area 3:
Sh eet Flow: Flow length = 300' = L
Slope = 2.4%
t1 = 0.449 hours = 26 .9 minutes
Shallow Concentrated Flow : Flow length = 370' = L
Slope = 3.2%
For unpaved s urface at 3 .2%, Velocity (V) = 2 .9 fps (see Fig . 3-1)
t, = 370' I (60*2.9) = 2.1 minutes
T c= 26 .9 + 2.1 = 29.0 minutes
Pre-Development Drainage Area 4:
Use Tc= 10.0 minutes
Post-Development
Time of Concentration Calculations
Refer to Exhibit B for flo w paths us ed for calculations.
Post-Development Drainage Area #1 OJ:
Sheet Flow: Flow length = 30' = L
Slope = 1.8%
n = 0 .24 , den se grass
P2 = 4.5"
ti = 0 .007 (0 .2 4 * 30)08
(4 .5)05 (0 .018)°"4
ti = 0.008 hours = 4 .8 minutes
Shallow Concentrat ed Flow: Flow length = 870' = L
Slope = 1.8 %
For unpaved surface at 1.8%, Velocity (V) = 2 .15 fp s (see Fi g. 3-1)
ti = 870' I (60*2 .15) = 6 .7 minutes
Tc= 4.8 + 6 .7 = 11.5 minutes
Post-Development Drainage Area #I 04:
Sh eet Flow: Flow length = 40 ' = L
Slope= 0.8%
ti = 0.139 hours = 8.3 minutes
Shallow Concentrated Flow: Flow length = 830' = L
Slope= 0.8 %
For unpaved surface at 0 .8%, Velocity (V) = 1.55 fps (see Fig . 3-1)
ti= 830' I (60* 1.55) = 8.9 minutes
Gutt er Flow: Flow length = 85' = L
**assuming flow in gutter is negligible**
Tc= 8.3 + 8 .9 = 17.2 minutes
Post-Development Drabtage Area #110:
Sh eet Flow: Flow length = 300' = L
Slope = 0.6%
t1 = 0.782 hour s= 46 .9 minutes
Shallow Concentrated Flo w: Flow length = 71 O' = L
Slope = 2.1 %
For unpa ve d s urfac e a t 2.1 %, Velocity (V) = 2.3 fp s (see Fi g . 3-1)
ti = 710' I (60*2 .1) = 5.1 minutes
T c= 46 .9 + 5.1 = 52.0 minutes
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-_________________ ...J
APPENDIXB
Storm Inlet Design Data & Calculations
12
North Forest Subdivision
I nlet Length Calculations -Revised 1212003
Inlets In Sump 10 year s torm 100 year storm
Inlet# Length Flow trom A c o,. °'~-0r .... Orot.i+t O"A Yto-ectu• L to.&q'd L 10.-1u.i o, .. o.,...., ..... Orotlll Orot••tO"I Ytoo
Area # (acres) (els) (els) from Inl et• (els) (els) (ft) (In) (ft) (ft) (els) (els) from lnletf (els ) (els) (ft) (In )
1 10' 106 1.53 0.55 7.27 7.27 7.99 0.3 17 3.80 9.79 9.79 10 .77 0.505 6.06 --5.99 10
0.00 0.55 0.00 0.00 0.00 0.000 0.00 0.00 0.00 0.00
6 10' 10 1 1.37 0.55 6.13 0.00 3 6.13 6.74 0.297 3.57 7.16 10 8.27 0.00 3 8.27 9.10 0.57 0 6.84 -----------------
107 0.54 0.55 . 2.56 2.58 2.82 0.214 2.57 3.48 3.4 6 3.80
• using 'I-a r • 0.583'
Inl ets On Grade 1 O year storm 100 year storm
Inle t #
2
3
5
"
Flow from
Length Yto
15'
15'
15'
15'
Ar ea # (ft) (In)
105 0.41 6 5.00 --104 0.383 ~ -10 2 0.369 4.43 -
10 3 0.368 4.41
T ra nsv erse (Crown) slope (fVft)
fo r 27' Street = 0 .033
o ... ,_ <lc..,..:lti Qbyp••
(ft) (els) (els)
0.7 1 10 .64 -2.00
0.68 10 .14 -2.49
0.66 9.94 -2.53
0.66 9.91 -2.59
Straight Cro wn Fl ow (Solved to find actual depth of flow, yl :
a= o.56 • (zln) • s "' · y'" ~ y = (0 / [0 .56 • (zln) • s "'ll "'
n =Roughness Coefficient= 0 .01 8
S = StreeUG utter Slope (fVft )
y = Depth of flow at inlet (ft)
Capac ity of Inl et s o n grade:
Oc = 0.7 • [1/(H , -H2)] • [H ,512-H2
512 ]
O c = Flow c apacity of inlet (els)
H 1 =a + y
H2 = a = gutter depression (2" Standard ; 4" Recessed)
y = Depth of flow in approach gutter (ft)
o.,,. ....
(els)
8.64
7.65
7.4 1
7.3 1
o.,...., ..... O tiyp-tot • Clcmpt-toti Q 10·Tot81 Ytoo
(els) j trom Inlet ti (els) (els) (els) (ft) (In)
0.00 8.64 8.64 0.466 5.59
0.00 2 0.00 7.65 7.65 0.4 33 5.19
0.00 7.41 7.4 1 0.4 13 4.96
0.00 7.3 1 7.31 0.411 4.93
z = Reciproc al of crown slope
for 27' Street = 30
Inlets In sumps. Weir Flow:
L = Q I (3 • y"2 ) ~ y = (QI 3L)213
L = Length of inlet opening (ft )
Q =Flow at inlet (els)
y = total depth of flow on inlet (ft)
max y for inl et in sump= T' = 0 .583'
o ... ,_ O up..:tty Qbyp•• Oc ..,1ut..:I Ocwry°"'
(ft) (els) (els) (els ) (els ) l ttom lnl91#
0.76 11 .4 1 0.24 11.41
0.72 10 .84 -0.48 10 .36 0.24 2
0.71 10.60 -0 .61 9.99
0.7 0 10.57 -0 .71 9.86
Qbn>-lot• O c..,t-totl 0 100.Tot.i s L .:1u.i
(els) (els) (els ) (ft/ft ) (ft)
0.24 11.41 11 .65 0.0090 15 --------
0.00 10.60 10.60 0.0 110 15 ---1--·-
0.00 9.99 9.99 0.0 125 ,_!_~ 9.86 0.00 9.86 0.0 125 15
North Forest Subdivision
De pth o f Flow in Gutter -Revised 1212003
(Refer to Exhibit B fo r Gu tter Locations)
10-y ear storm 100-year storm
Gutter A c Locat ion (a cres )
A1 0 .73 0 .55 ------------·-
A2 0.71 0.55 ----·
A3 1.56 0 .55
A4 1.54 0 .55 --
81 1.37 0 .55
82 0 .54 0 .55
83 2.07 0.55
C1 1.82 0 .55
C2 1.53 0 .55
C3 1.82 0 .55 -----
C4 1.53 0 .55
01 0 .77 0.55
0 2 0 .83 0 .55
Tra nsve rse (Cro wn) slo pe (ft/ft)
27' street = 0 .0330
Slope 0 10
(ft/ft) (cfs)
0 .0143 3 .47 --------
0 .0143 3 .37
0.0125 7.41
0.0125 7 .31
0 .0115 6 .51
0.0110 2.56
0 .0110 7 .65
0 .0090 8 .64
0 .0180 7 .27
0 .0140 8 .64
0.0140 7 .27
0 .0080 3 .66
0 .0080 3 .94
Y10..ac1ua l 0 100
(ft) (i n) (cfs)
0 .271 3 .25 4 .67 ---------------
0 .268 3.22 4 .55
-------·--
0 .369 4.43 9 .99 -------
0 .368 4.41 9 .86 ----------
-------
0 .357 4.29 8 .77 --
0 .254 3.05 3.46
0 .383 4.60 10 .36
---
0.416 5 .00 11 .65 ---
0 .343 4.11 9 .79 ---
0 .383 4 .60 11 .65 ---· --·---.
0 .359 4 .31 9 .79
·----
--
0 .308 3 .70 4 .93
0 .317 3.80 5 .31
Str ai ght C r own Flow (Solved to find actual d e pth of flow i n gutter, y):
Q = 0 .56 * (z/n) * 5 112 * y813 ¢ y ={Q I (0.56 * (z/n) * 5 112 ]}318
n =Rou ghness Co efficie nt= 0 .0 18
S = Street/Gutter Slope (ft/ft)
y = Depth of flo w at inlet (ft)
z = Reciproca l of c row n slope:
27' street = 30
Y100
(ft) (in)
0 .303 3.64 ---
0.300 3 .60
---
0.413 4 .96 -------·
0.411 4 .93 ---
-----
0.400 4 .80
··---
0 .284 3.41
-----
0.429 5 .15 ·-
·-----
0 .466 5.59 ------
0 .383 4 .60
-
0.429 5.14
---
0.402 4 .82 -----
------
0.345 4 .14 --·--~
0 .355 4 .26
APPENDIXC
Storm Pipe Design Data & Calculations
l 'i
North Forest Subdivision
Pipe Calculations -Revised 1212003
Inlet Outlet 10 year storm 100 year storm Pi pe /Box# Size Length Slope
Invert Elev Invert Elev *Actual Flow Design Flow V10 Travel T ime , t11 0 *Actual Flow Design Flow V100 %Full
(in) (ft) (%) (ft) (ft) (cfs) (cfs) (fps) (sec) (min) (cfs) (cfs) (fps)
1 5x2 245.7 0 .35 242 .73 241 .87 46 .97 6 .1 77 .2 40 0 .67 63 .38 6 .6 -
2 5x2 73 .3 0 .25 242 .\'.)6 242 .78 39 .70 5 .1 77.2 14 0 .24 53 .59 5 .6 ---
3 4x2 165.3 0 .30 243 .51 243 .01 31 .06 5 .2 74 .3 32 0 .53 42 .18 5 .7 --
4 27 34 .4 0.45 244 .05 243 .90 14 .72 5 .3 65.4 6 0 .11 19 .85 5 .5 -- -·-
5 24 3 1.2 0.55 244.47 244 .30 7.41 11 .97 5 .5 65 .7 6 0 .09 9 .99 16 .13 5.6 ---
6 27 10 5 .6 0 .25 243 .82 243 .56 8 .69 3 .8 56 .1 28 0.46 11 .73 4 .0
·These values reflect the actual flow for the 18" & 24 " pipes . The design flow for these pipe sizes reflects a 25% reduction in pipe area .
(Refe r to attached calculat ion for specific information .)
% Full
95 .7
95 .7
93 .0
84 .8
85 .6
68.6
Travel T ime, tnoo
(sec) (min)
37 0 .62
13 0.22
29 0.48
6 0.10
6 0 .09 -
26 0.44
City of College Stati o n requ i r ement t o Reduce Cross-Sectional Area of 18" & 24" Pipes by 25%
Using Mannings Equation from page 48 of the College Station Drainage Policy & Design Standards Manual :
Q = 1.49/n *A * R213 * S 112
Q = Flow Capacity (cfs)
18" P ipe:
Pipe size (inches)= 18
Wetted Perimeter WP , (ft)= 4.71
Cross-Sectional Area A , (tt2) = 1.766
Reduced Area AR, (ft2 ) = 1.325
Hydraulic Radius R = A/WP • (ft) = 0 .375
Reduced Hydr Radius RR= ARM/p , (ft)= 0 .281
Roughness Coefficient n = 0 .014
Fr iction Slope of Conduit S1, (ft/ft) = 0 .01
Example Calculation :
S lope Flow Capacity Reduced Flow Capacity % D ifference
s Q Ored uced Oreduced/Q
0 .005 6 .91 4.28 0.619
0 .006 7 .57 4 .69 0.61 9
0 .007 8.18 5 .06 0.619
24" P ipe:
Pipe size (inches)= 24
Wetted Perimeter WP, (ft)= 6.28
C ro ss-Sectio nal Area A, (ft2 ) = 3.14
Reduced Area AR. (ft2 ) = 2.355
Hyd raulic Radius R =A/WP, (ft)= 0.5
Reduced Hydr Radius RR= ARM/p , (ft)= 0.375
Roughness Coefficient n = 0.0 14
Friction Slope of Conduit Sr. (ft/ft)= 0.01
Example Calculation :
Slope Flow Capacity Reduced Flow Capacity % Difference
s Q O reduced Oredu ced /Q
0.005 14 .89 9 .22 0.6 19 -----------
0 .006 16.31 10.1 0.619 -------------·---------
0 .007 17 .61 10.9 0.61 9
Co nclusion:
Mu ltiply actua l Q in 18" & 24" pipes by 1.615 to reflect a 25% reducti on in the
cross-sectional area called for on page 47 , paragraph 5 of the Colleg e Station
Drain age Policy & Design Standards manual.
North Forest Subdivision
Pipe Flow Diagram -Revised 1212003
010 (cfs)
Inlet 5 I 7.41
J,
Pipe 5 I 7.41
J,
Inlet 4 I 7 .31
J,
Pipe 4 l 14 .72 Inlet 6 I 8 .69
J, J,
Inlet 3 I 7 .65 Pipe 6 I 8 .69
J,
Box 3 I 31 .06
J,
Inlet 2 I 8 .64
J,
Box 2 I 39.70
J,
Inlet 1 I 7.27
J,
Box 1 I 46 .97
-1
II Existing C hannel II
North Forest Subdivision
Pipe Flow Diagram -Revised 1212003
0 100 {cfs}
Inlet 5 I 9 .99
J,
Pipe 5 I 9 .99
J,
Inlet 4 I 9 .86
J,
Pipe4 I 19 .85 Inlet 6 I 11 .73
J, J,
Inlet 3 I 10 .60 Pipe 6 I 11 .73
J,
Box 3 I 42 .18
J,
Inlet 2 I 11.41
J,
Box2 I 53 .59
J,
Inlet 1 I 9 .79
J,
Box 1 I 63.38
J,
II Existi ng Channel II
Box 1 -1 0 Year Storm
Manning Pipe Calculator
Giv en Input Data:
Shape .......................... .
Solving for .................... .
He ight ......................... .
Width .......................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Computed Results:
Depth ......................... : .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Rectangular
Depth of Flow
24 .0000 in
60.0000 in
46.9700 cfs
0.0035 ft/ft
0 . 0140
18.5208 in
10.0000 ft2
7 .7170 ft2
97 .0 4 16 in
168 .0000 in
6 .0866 fps
11.4512 in
77 .1699 %
50.1772 cfs
5 .0177 fps
Box 1 -100 Year Storm
Manning Pipe Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Height ......................... .
Width .......................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Computed Results:
Depth .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flo w v elocity ............. .
Rectangular
Depth of Flow
24 .0000 in
60 .0000 in
63 .3800 cfs
0 .0035 ft/ft
0 . 0140
22.9584 in
10.0000 ft2
9.5660 ft2
105 .9167 in
168 .0000 in
6.6256 fps
13.0055 in
95 .6599 %
50 .17 72 cfs
5 .0 17 7 fp s
Nort h Forest S ub d ivision -Revised 1 2 /2 0 03
College Sta i o n, Tex as
Box 2 -10 Year Storm
Manning Pipe Calculator
Given Input Data :
Shape .......................... .
Solving for .................... .
Height ......................... .
Width .......................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Computed Results :
Depth ......................... : .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Rectangular
Depth of Flow
24 .00 00 in
60.0000 in
39.7000 cfs
0 .0025 ft/ft
0. 0140
18 .521 8 in
10.0000 ft2
7.7174 ft2
97 .043 6 in
168 .0000 in
5 .1442 fps
11 . 4516 in
77 .1742 %
42.4074 cfs
4.2407 fps
Box 2 -100 Year Storm
Manning Pipe Calculator
Given Input Data :
Shape .......................... .
Solving for .................... .
Height ......................... .
Width .......................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Computed Results:
Depth .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Rectangular
Depth of Flow
24.0000 in
60.0000 in
53 .59 00 cfs
0 .0025 ft/ft
0 .0140
22.9659 in
10.0000 ft2
9 .56 91 ft2
105 .9 317 in
168 .00 00 in
5.6003 fps
13 .0 079 in
95. 69 11 %
42.4074 cfs
4.2407 fps
Nor th Forest S ubdi visio n -Re vi sed 12 /2 0 03
College S t at i on, Tex a~
Box 3 -10 Year Storm
Manning Pipe Calculator
Given Input Dat a:
Shape .......................... .
Solving for .................... .
Height ......................... .
Width .......................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Computed Result s:
Depth ......................... : .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Rectangular
Depth of Flow
24.0000 in
48 .0000 in
31 .0600 cfs
0.0 030 ft/ft
0. 0140
17 .8278 in
8.0000 ft2
5.94 2 6 ft2
83 .6 555 in
144.0000 in
5 .226 7 fps
10.2292 in
74.2823 %
35 .493 4 cfs
4.4367 fps
Box 3 -100 Year Storm
Manning Pipe Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Height ......................... .
Width .......................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Computed Results :
Depth .......................... .
Area ........ : .................. .
Wetted Area .................... .
Wetted Perimete r ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow veloci t y ............. .
Rectangular
Depth of Flow
24.0000 in
48.0000 in
42.1800 cfs
0 .0030 ft/ft
0 . 0140
22.3115 in
8 .0000 ft2
7 .4372 ft2
92 .623 1 in
144 .00 00 in
5 .6715 fps
11.56 2 5 in
92.9648 %
35 .4934 cfs
4.43 67 fps
Nor th Forest Subd i visi o n -Revised 12 /2 0 03
Col]ege Sta i on . T e >:a~;
Pipe 4 -10 Year Storm
Manning Pipe Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Di ameter ....................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Computed Results :
Depth .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hy draulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Circular
Depth of Flow
27 .0000 in
14.7 2 0 0 cfs
0 .00 4 5 ft/ft
0 . 0140
17 .6578 in
3 .9761 ft2
2.7551 ft2
50 .8644 in
84 .8230 in
5.34 2 8 fps
7 .7 9 9 9 in
65 .3991 %
19 .2 915 cfs
4 .8519 fps
Pipe 4 -100 Year Storm
Manning Pipe Calculator
Giv en Input Data:
Shape .......................... .
Solving for .................... .
Diameter ....................... .
Flowrate ....................... .
Slope .......................... .
Manning ' s n .................... .
Computed Results:
Depth .......................... .
Area ......................... · · ·
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hy draulic Radius ............... .
Percent Full ................... .
Full flow Fl o wrate ............. .
Full flow v eloc i t y ............. .
Circular
Depth of Flow
27.0000 in
19.8500 cfs
0.0045 ft/ft
0 . 0140
22.9057 in
3 .9761 ft2
3 .5961 ft2
63.2234 in
84 .8230 in
5 .5198 fps
8.1 907 in
84.8 3 59 %
19 .2 915 cfs
4 .8519 fps
Nort h Fores t S ubdivis i on -Revised 12 /2 003
('r,l l e ge Stati o n, T e xi'l~>
Pipe 5 -10 Year Storm
Manning Pipe Calculator
Gi v en Input Data :
Shape .......................... .
Solving for .................... .
Diameter ....................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Computed Results:
Depth .......................... .
Area ......... : .................. .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Circular
Depth of Flow
24.0000 in
11.9700 cfs
0 .0055 ft/ft
0.0140
15.7730 in
3.1416 ft2
2.1891 ft2
45.3754 in
75.3982 in
5 .4680 fps
6 .9472 in
65 .7210 %
15.5788 cfs
4.9589 fps
Pipe 5 -100 Year Storm
Manning Pipe Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Diameter ....................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Computed Results:
Depth .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow v elocity ............. .
Circular
Depth of Flow
24.0000 in
16 .1300 cfs
0 .0055 ft/ft
0.0140
20.5340 in
3.1416 ft2
2.8619 ft2
56 .6870 in
75.3982 in
5.6361 fps
7.2700 in
85.5585 %
15.5788 cfs
4 .9589 fps
North Forest Subdi v ision -Revised 12 /2003
College Stat i o n, T e xas
Pipe 6 -10 Year Sto rm
Manning Pipe Cal c ulator
Giv en Input Data:
Shape .......................... .
Solving for .................... .
Diamete r ....................... .
Flowrate ....................... .
Slope .......................... .
Manning ' s n .................... .
Computed Results :
Depth .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Circular
Depth of Flow
2 7 .00 00 i n
8 .6 9 00 c fs
0 .00 25 f t/ft
0 .0140
15 .1 4 17 in
3 .9761 ft 2
2.2 951 ft2
45.7030 in
84 .8 2 30 i n
3.7863 fps
7 .23 13 in
56 .080 3 %
14.3 7 91 cfs
3.6164 fps
Pipe 6 -100 Year Storm
Manning Pipe Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Diameter ....................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Computed Results:
Depth .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowra te ............. .
Full flow v e l o c ity ............. .
Circula r
Depth of Flow
27 .0000 in
11.7300 cfs
0 .0025 ft/ft
0. 0140
18 .5330 in
3.9761 ft2
2.9094 ft2
52 .7266 in
84 .8230 in
4.0318 fps
7.9 4 57 i n
68 .6408 %
14 .3 7 9 1 cfs
3.6164 f ps
Nor th Forest S ubd ivis i on -Revised 12 /2003
College Sta ti on, T e x as
EXHIBIT A
Pre-Development Drainage Area Map
Drainage Report
for
North Forest Subdivision
College Station, Texas
November 2003
Developer:
North Forest, LLC
420 Tarrow Street
College Station, Texas 77840
Prepared By:
TEXCON General Contractors
1707 Graham Road
College Station, Texas 77845
(979) 764-7743
s~
8:ao~
ll~\'3-oa
OS·2'#~
CERTIFICATION
I, Joseph P . Schultz, Licensed Professional Engineer No. 65889, State of Texas , certify that this report
for the drainage design for the North Forest Subdivision in Co lle ge Station, Texas, was prepared by me
in accordance with the provisions of the City of Co ll ege Station Drainage Policy and Design Standards
for the owners hereof, with the exception that stonn water runoff detention is not being required for
this proj ect since the site discharges directly into an existing drainage and immediate ly into the 100-
year floodplain limits .
TABLE OF CONTENTS
NORTH FOREST SUBDIVISION
CE RTI FICAT IO N .................................................................................................................................................................. 1
TABLE OF C O NTENTS ........................................................................................................................................................ 2
LIST OF TABLES .................................................................................................................................................................. 2
I NT ROD UCT IO N ................................................................................................................................................................... 3
GENE R AL LOCATION AND DESCRIPTION .................................................................................................................. 3
FLOOD HAZARD I NFORMATIO N .................................................................................................................................... 3
DEVELOPMENT DRAINAGE PATTERNS ....................................................................................................................... 3
DRAIN AGE DESIGN CRITERIA ........................................................................................................................................ 3
STORM WATER R UN OFF DETE RMINAT IO N ............................................................................................................... 5
STORM SEWER DESIGN .................................................................................................................................................... 6
CONCLUSIONS ..................................................................................................................................................................... 6
APPEND I X A .......................................................................................................................................................................... 7
Tim e of Co11centratio11 Equations & Calculation s
APPENDIX B ........................................................................................................................................................................ 11
Storm Inlet Design Data & Calculations
A PP EN DIX C ........................................................................................................................................................................ 14
Storm Pip e Design Data & Calculations
EXHlBIT A ............................................................................................................................................................................ 24
Pre-Developm ent Drainage Area Map
EXHIBIT B ............................................................................................................................................................................ 26
Po st-Developm ent Drainage Area Map
LIST OF TABLES
TABLE 1 -Rainfall Intensity & Runoff D ata .......................................................................................... 4
TABLE 2 -Time of Concentration (tc) Equations .................................................................................. 4
TABLE 3 -Post-Developm ent Drainage D ata ........................................................................................ 5
TABLE 4 -Pre-vs . Post-Development Off-Site Runoff ......................................................................... 5
INTRODUCTION
DRAINAGE REPORT
NORTH FOREST SUBDIVISION
The purpose of this report is to provide the hydrological effects of the construction of the North
Forest Subdivision , and to show that the storm water runoff will be controlled in such a manner
so as to have minimal offsite or downstream impact. This report does not address the future
development of Lot 1, Block l of the subdivision. This lot is zoned A -P and the drainage from
this lot will need to be addressed at the time of it's development.
GENERAL LOCATION AND DESCRIPTION
The project is located on a 20.8 acre tract located in Co ll ege Station, Texas. Most of the site is
open land with grass . Approximately 2.4 acres on the southwest end along Bee Creek are being
dedicated as greenway. This area is partially wooded. The existing ground elevations range
from elevation 238 to elevation 260. 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 Bee Creek Drainage Basin. A portion of the site is located in a
Special Flood Hazard 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 48041C0163-D. Three of these Special Flood Hazard
Areas are located on the property. Flood Zone AE areas are inundated by the 100-year flood
with base flood elevations determined. Flood Zone X Shaded are areas of the 500-year flood
and areas of the 100-year flood with average depths of less than l foot or with drainage areas
less than l square mile, and areas protected by lev ees from the 100-year flood. Flood Zone X
Unshaded areas are determined to be outside of the 500-yr floodplain. These floodplain areas
are shown on Exhibit A. All of the 100-year floodplain area for this tract is located within the
Greenways Dedication Area.
DEVELOPMENT DRAINAGE PATTERNS
A portion of the pre-development storm water runoff from the site flows southeast directly into
the 100-year floodplain and Bee Creek, while the majority of the runoff from the pre-
development area flows to the northeast to the adjacent property, and then into the 100-year
floodplain . After development, these conditions will be changed such that only a small portion
of the developed area will continue to flow onto the adjacent property, and the majority of the
runoff will be captured by the storm sewer system and discharged directly into Bee Creek .
Because of these conditions, no detention is required for this development. The pre-
development drainage area boundaries are shown on Exhibit A, and the post-development
drainage area boundaries are shown on Exhibit B.
DRAINAGE DESIGN CRITERIA
Th e design paramet e rs for the storm se we r ar e as fol lows :
• The Rational Method is utili zed to d e te rmine p eak stotm water runoff rates for the
stom1 sewer design .
• Design Stonn Frequency
Storm sewer sys te m
• Runoff Coefficients
Single Fami ly Res id e ntial
Undeve lop ed
10 and 100 -year stonn event s
c = 0.55
c = 0.30
• Rainfall Intensity equations and va lu es for Brazos County can be found in Table 1.
• Time of Concentration, tc -Calculati ons are bas e d 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-development time of concentration is
shown in Ex hibit A , and the flow paths used for the post-development tim es of
concentration are found in Exhibit B. For smaller drainage areas, a minimum tc of 10
minutes is used to determine the rainfall intensity valu es.
TABLE 1 -Rainfall Intensity & Runoff Data
Rainfall Intensity Values
(in/hr)
Storm
Event
Is
110
hs
lso
1100
Brazos
County:
5 vear storm
b = 76
d = 8 .5
e = 0 .785
t c =
10 min
7.693
8.635
9 .861
11 .148
11 .639
10 'i.ear storm
b= 80
d = 8 .5
e= 0 .763
I = b I (tc+d)"
I = Ra infa ll Intens ity (in/hr)
tc = U(V*60)
tc =Time of concentration (min)
L = Length (ft)
V =Velocity (ft/sec)
25 'i.ear storm 50 'i.ear storm 100 'i_ear storm
b = 89 b = 98 b= 96
d= 8 .5 d= 8 .5 d= 8 .0
e= 0.754 e= 0 .745 e= 0 .730
(Data taken from State Department of Highwa'i.S and Public Transportation H'i_draulic Manual, pag e 2-16)
TABLE 2 -Time of Concentration (tc) Equations
The tim e of concentration was determin ed using methods found in TR-55, "Urba n
Hydrolo gy for Small Watersheds. " The equations are as follows:
Time of Con centration : Tc = Tt(s hcer llo\\) + Tr(co nct'nl rolll'll s lH .. 'l'I n o\\)
w here : T 1 =Trave l Time , minute s
For S heet Flo w : 0.007 (n L)0·8
(Pz)o.s 5o.4 w h e re : T 1 =trave l time , h ours
n =M a nn in g 's roug h ne ss co e ffi c ie n t
L = fl ow leng th , fee t
P2 = 2-year, 24 -ho u r rai n fa ll = 4 .5 "
s = la nd s lo pe , ft/ft
For S ha ll ow C o n c e n trated F low : T 1 =L I (6 0 *V)
Refer to App e ndi x A fo r ca lc ul at io ns .
ST O RM WATE R R UN O FF DETERMINATI O N
w he re : T 1 =tra ve l time , minu te s
V =Ve loc ity , fp s (S e e F ig 3-1 , Ap p . E )
L = fl ow length , feet
T he peak runoff valu es w ere d etermin ed in accord ance with th e criteria pres ent ed in th e
previo us s ection for th e 5 , 10 , 25 , 50 , and 100-yea r s torm eve nts . The runoff co e ffici e nt s
are based on the futur e d eve lopm e nt of thi s tract , and the peak runoff va lu es determined for
th e post-development condition are sho w n in T abl e 3.
TABLE 3 -Post-Deve lopme nt D ra in age D ata
Area c 5 year sto r m 10 year s t o rm 25 year sto rm 50 yea r storm 100 year storm
le Area# (acres ) Is Os 11 0 0 10 l2s 0 2s lso Oso 11 00
A,_
C1 C2 Crotal A, Tota l (m i n ) (in /h r ) (cfs) (in/h r) (cfs) (in /hr) (cfs) (i n/hr) (cfs) (in /hr)
101 1.37 0 1.37 0 .55 0 .3 0 .55 11.5 7.236 5 .4 5 8 .136 6 .13 9 .299 7.0 1 10 .5 19 7 .93 10 .979
102 1.56 0 1 .56 0 .55 0 .3 0 .55 10 7.693 6 .60 8 .635 7.4 1 9 .86 1 8.46 11 .148 9 .56 11 .639
103 1 .54 0 1.54 0 .55 0 .3 0 .55 10 7 .693 6 .52 8 .635 7 .3 1 9 .86 1 8 .35 11 .148 9.44 11 .639
104 2 .0 7 0 2.07 0 .55 0 .3 0 .55 17.2 5 .943 6 .77 6 .7 19 7 .65 7.697 8 .76 8 .726 9 .9 3 9 .104
105 1.82 0 1.82 0 .55 0 .3 0 .55 10 7 .693 7.70 8 .635 8 .64 9 .861 9 .87 11 .148 11 .16 1 1.639
106 1 .53 0 1.53 0 .55 0 .3 0 .55 10 7 .693 6 .4 7 8 .635 7 .27 9 .861 8 .30 11 .148 9 .38 1 1.639
107 0 .65 0 0 .65 0 .55 0 .3 0 .55 10 7.693 2 .75 8 .635 3 .09 9 .861 3.53 11 .148 3 .99 11 .6 39
The pre-devel opment area flowing offsi te onto th e adjacent property is 10 .5 acres and is
shown on Exhi b it A. After development, the area flowing offsite is reduced to 2.02 acres ,
as shown on Exhibit B. Table 4 compares the pe ak runoff values for each of th ese
conditions , verifying th at th e po st -dev e lopment o ffsite flo w is less than the pre-
development offsite flow .
TABLE 4 -Pre-vs. Po st-D eve lopm en t O ff-S ite R unoff
0 100
(cfs)
8 .27
9 .99
9 .86
10 .37
1 1.65
9 .79
4 .16
Area c 5 yea r sto rm 1 O yea r storm 25 year s t o rm 50 year stor m 100 year storm
le Area# {a c res) Is Os 110 0 10 l2s 02s l so O so 1100 0 100 C 1 C2 Crotal
{cfs) A 1 A2 Total (mi n ) (in/h r ) (cfs) (i n /hr) (cfs) (i n/hr) {cf s) (i n/hr) (cfs) (in/hr)
P re-d evel 10 .50 0 10.50 0 .30 0 0 .30 40 .2 3 .598 11.33 4 .126 13 .00 4 .753 14.97 5 .420 17 .07 5 .6 7 1 17 .86 --------
Pos t-deve l 2 .02 0 2 .02 0 .55 0 0 .55 10 7 .69 3 8 .5 5 8 .635 9 .59 9 .86 1 10 .96 1 1.14 8 12.39 11 .639 12 .93
Reduction in Off-si te Flow Aft er Deve lopment of the Propert y : 2 .79 3 .4 0 4 .0 2 4 .69 4 .93
STORM SEWER DESIGN
The storm sewer piping for this proj ect has been selected to b e Reinforced Concrete Pipe
(RCP) meeting the requirements of ASTM C-76 , Class III pipe and pre-cast Bo x Sections
meeting the requirements of ASTM C-789 . The curb inlets will be cast-in-place concrete .
Appendix B presents a summary of the stonn sewer inlet desi gn param eters and
calculations. The inl ets were designed based on a 10-year d esig n storm . As pe r Co ll ege
Station guidelines, the capacities of inl ets in sump were reduc ed by 10 % to allow for
clogging.
Inlets were located to maintain a gutter flow depth of 5" or less , which will prevent th e
spread of water from reaching the crown of the road for the 10-year storm event. Refer to
Appendix B for a summary of the gutter flow depths at various locations . The runoff
intercepted by the proposed storm sewer inlets was calculated using the following
equations. The depth of flow in the gutter was determined by using the Straight Crown
Flow equation. The flows intercepted by Inlets 2, 3, 4, & 5 were calculated by using th e
Capacity of Inlets On Grade equation. The capacity for the inlet in sump (Inlet 1) was
calculated using the Inlets in Sumps, Weir Flow equation with a maximum allowable depth
of 7" (5" gutter flow plus 2" gutter depression). These equations and the resulting data are
summarized in Appendix B. The area between the right-of-way and the curb line of th e
streets will be filled as necessary to provide a minimum of 6" of freeboard above the curb
line . This will ensure that the runoff from the 100-year storm event will remain within the
street right-of-way.
Appendix C presents a summary of the storm sewer pipe design parameters and
calculations. All pipes are 18 " in diameter or larger. For pipes with 18 " and 24"
diameters, the cross-sectional area is reduced by 25%, as per College Station requirements .
A summary of how this was achieved is shown in Appendix Caswell. The pipes for the
storm sewer system were designed based on the 10-year storm event; however, all will also
pass the 100-year storm event without any headwater. As required by College Station, th e
velocity of flow in the storm sewer pipe system 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 and boxes will exceed 2.5 feet per second and prevent sediment
build-up in the pipes and boxes. The maximum flow in the storm sewer pipe system will
occur in Box 1. Appendix C contains a summary of the Manning pipe calculations as well
as flow diagrams mapping the flows through the storm sewer system for the 10 and 100-
year events . The max imum velocity for the pipe system will be 6 .6 feet per second and
will occur in Box 1.
CONCLUSIONS
The construction of this project will increase the storm water runoff from this site.
However, a majorit y of the runoff will be carried through a storm sewer system direc tl y to
Bee Creek and imm ediat e ly into the 100-year floodplain. The remaind e r of th e runoff will
flow onto th e adjacent prop erty and th en into th e I 00-year floodplain . As not ed
prev iousl y, this runoff is less th an th e pre -development runoff onto thi s prop e rt y. T he
in c reased fl ow in Bee C reek sho uld not have a sign ific a nt imp ac t on th e s urroundin g
property . No flood damage to down s tr ea m or adjacent landowners is ex pect ed as a res ult
of thi s deve lopm e nt.
APPENDIX A
Time of Concentration Equations & Calculations
7
Pre-Development
Time of Concentration Calculations
Ref er to Ex hibit A fo r flow path used for calc ula ti ons .
Pre-Developm ent Drainage Area :
Sh eet Flow : F low le ngt h = 300 ' = L
S lope = 1.36%
n = 0 .24 , den se g ra ss
P2 = 4.5''
ti = 0.007 (0 .24 * 300)08
(4.5)05 (0 .0136)04
ti= 0.564 hours = 33.8 minutes
Shallow Concentrated Flow : Flow len gt h = 785' = L
S lope = 1.6%
For unpaved s urface at 1.6%, Velocity (V) = 2 .0 5 fp s (see Fi g. 3-1)
ti = 785' I (60*2.05) = 6.4 minutes
T c= 33.8 + 6.4 = 40.2 minutes
Post-Development
Time of Concentration Calculations
Refer to Exhib it B for flow path us ed for calculat ions.
Drainage Area #101 :
Sheet Flow: F low len gth = 30 ' = L
Slope = 1.8 %
n = 0 .24, den se grass
P2 = 4.5"
t, = 0 .007 (0 .24 * 30)°8
(4.5)05 (0.018)04
t1 = 0.008 hours= 4 .8 minutes
Shallow Concentrated Flow: Flow length = 870' = L
Slope= 1.8 %
Drainage Area #104 :
Sh eet Flow:
For unpaved s urface at 1.8%, Velocity (V) = 2 .15 fps (see Fig . 3-1)
~ t1 = 87 0 ' I (60*2.15) = 6 .7 minutes
Tc= 4.8 + 6 . 7 = 11.5 minutes
Flow length = 40 ' = L
Slope= 0.8%
n = 0 .24, den se grass
P2 = 4.5"
t, = 0.007 (0 .24 * 40)°8
(4.5)0·5 (0.008)04
t1 = 0.139 hours = 8 .3 minutes
Shallow Concentrated Flow: Flow length = 830' = L
Slope= 0 .8%
For unpaved surface at 0.8%, Velocity (V)= 1.55 fps (see Fig . 3-1)
t1 = 830' I (60* 1.55) = 8.9 minutes
Gutter Flow: Flow length = 85' = L
**ass uming flow in gutter is negligible**
Tc= 8 .3 + 8 .9 = 17.2 minutes
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APPENDIX B
Storm Inlet Design Data & Calculations
11
North Forest Subdivision
Inlet Length Calculations
Inlets In Sump 10 year storm 100 year sto rm
Inlet#
1
Inlet#
2
J
s
J
Flowtrom A c 0 10 C urry-Orot81 Orot81+10% Y10.-c1u111 l 10""-eq'd L 10--etu.i 0 100 O cwryOYW Length
Area# (acres) (els) (cfs) I from Inlet I (clsl (els) (ft) I (I n) (ft) (ft) (els) (e ls ) I from Inlet#
t O' 106 1.S3 0 .SS 7.27
-I ,__!_;E_ 7.99 0 .317 I 3.80 S.99 10 9 .79 I -----
0 .00 0 .SS 0 .00 0 .00 0 .00 0 .000 I 0 .00 0 .00 I
Inlets On Grade 1 a year storm
Flowtrom
Length Y10 O pertoot O c..,.:11 abyp... O c.,:ilured O cwryo...., O byp-tota O c99t-toU 0 10-To•• Y100 Q J*'IOOI
Area# (ft) (In) (ft) (els) (els ) (els) (els ) Ir.om lnlel# (els ) (els ) (els ) (ft) (I n) (ft)
1S' 10 S 0 .416 ~~~ -2 .00 8.64 I o .oo 8.64 8.64 ~ s .s9 o.76
1S' 104 o .383 4.60 o .68 10 . 14 -2.49 7.6S o.oo I 2 o .oo 7.6s 7.6s 0.429 s .1s 0.72
1S' 102 0 .369-4.43 0 .66 ~ -2 .S3 ~==-:J __ -__ 0 .00 'i4'1" ~ 0 .413 ~ 0.71
o .368 4.41 0 .66 9.91 -2.S9 7.31 ---i · o .oo 7.31 I 7.31 0.411 4.93 o.70 1S' 103
Transverse (Crown) slope (ft/ft)
for 27' Street = 0 .033
Strai ght Crown Flow (Solved to find actual depth of flow, y):
a= o .56 • (zln) • s '" · y'" q y =(Q t [0 .56 • (zln) • s "'n'"
n =Roughness Coeffi c ient= 0 .018
S = StreeUGutter Slope (ft/ft)
y = Depth of flow at inlet (ft)
Capacity of Inlets on grade:
Oc = 0 .7 • [1 /(H 1 • H2)] '[H 1
512 • H,512 ]
Oc = Flow cap acity of in let (cfs )
H , =a + y
H, =a= gutter depression (2" Standard ; 4" Recessed)
y = Depth of flow in approach gutter (ft)
z = Rec iprocal of crown slope
Cor 27' Street = 30
Inlets In sumps, Weir Flow:
L = Q I (3 • y312 ) q y = (QI 3L)213
L = Length oC inlet opening (ft)
Q = Flow at inlet (els)
y = total depth of flow on inlet (fl)
max y tor inlet in sump = r = 0 .583'
Oro111 Oro1111•1°" Y1 00
(els) (els) (ft) I (In)
9.79 10 .77 o.sos J 6.06
0 .00 0 .00
100 year storm
QC llfllCHy abyp... O ctiph.Ked .,._ __ o._._..,_._._. _ _, Otryop·lot ..
(els) (els) (els ) (els) I •••m '"~" (els ) (els) (els)
11.41 0.24 11.41 0 .24 11.4 1 11 .6S l~'-"'--l-'-"-'-'--1------~·I---~'--
s
(tuft)
0 .0090
(ft)
1S
10 .84 -0.48 10 .36 0 .24 2 0.00 10 .36 10 .36 0 .0 110 1S
10 .60 -0 .61 9.99 0.00 9 .99 9 .99 0 .0 12 S 1S
·~--1~---1----+----··----~ -~
10 .S7 -0 .71 9 .86 0.00 9 .86 9.86 0.0 12S 1S
North Forest Subdivision
Depth of Flow in Gutter
(Refer to Exhibit B for Gutter Locations)
10 -year storm
G utte r A c Locat i o n (acres )
A1 0 .73 0.55
A2 0 .71 0 .55
---
A3 1.56 0 .55 ---- -
A4 1.54 0.55 ----· --
------
81 1.37 0 .55 -----------
82 0 .65 0 .55 ----------------
83 1.56 0 .55 ----------
84 2 .07 0 .55 ------------
--------------
C1 1.82 0 .55 ----------
C2 1.53 0 .55 --------------
C3 1.82 0 .55 ---------------
C4 1.53 0 .5 5
--
01 0 .77 0 .55
--
02 0.83 0 .55
Transverse (Crown) slope (fUft)
27' street= 0 .0330
Slo pe 0 10 Y10 -ac lu a l
(ftlft) (cfs) (ft) (i n)
0 .0143 3.47 0 .2 71 3.25
-· -· --
0 .0143 3.37 0 .268 3 .22 - -
..
0 .0125 7.41 0 .369 4.43 ------
0 .01 25 7 .3 1 0 .368 4.41 ---
- -
------
0.0110 6 .51 0 .360 4 .33 ------------ -
0.0110 3.09 0 .273 3.27 --------. - -
0.0110 7.41 0 .378 4 .54 ------------------
0 .0110 7 .65 0 .383 4 .6 0 ---·-----------
--·-------------
0.0090 8 .64 0.416 5.00 ------·-----------
0.0180 7 .27 0 .343 4 .11 -------------
0.0140 8.64 0 .383 4 .60 -------------·---------
0 .0140 7 .27 0 .359 4 .31 -------·---
0.0080 3.66 0.308 3 .70
-
0 .0080 3 .94 0 .317 3.80
Straight Crown Flow (Solved to fi nd actual d e pth of flow i n gutter, y):
Q = 0.56 * (z/n) * S112 * y8'3 ¢ y ={QI (0.56 * (z/n) * S112 ]}318
n = Roughness Coefficient= 0 .018
S = StreeUGutter Slope (fUft)
y = Depth of flow at inl et (ft)
z = Reciprocal of crown slope :
27' street = 30
100-year storm
0100 Y100
(cfs) (ft) (in)
4 .67 0 .303 3.64
4 .55 0 .300 3.60
9.99 0.413 4 .96
9 .86 0.41 1 4 .93
8 .77 0.403 4 .8 4
4 .16 0 .305 3 .6 6 ---
9 .99 0.423 5 .08 - -----
10 .36 0.429 5.15 -·-----
- - -
11 .65 0 .466 5.59
--·--
9 .79 0 .383 4 .60 -
11 .65 0.429 5.14 -.. -
9 .79 0.402 4 .82 -----
----·---
4 .93 0.345 4 .14 ----·-----
5.31 0 .355 4 .26
APPENDIXC
Storm Pipe Design Data & Calculations
1-l
North Forest Subdivision
Pipe Calculations
Pi pe /Box# Size Length Slope
(in) (ft) (%)
1 4x2 24 9 .1 0.40
--·-
2 4x2 72 .7 0 .30
Inlet
Invert Elev
(ft)
242 .85
~·
243 .12
Outlet 10 year storm
Invert Elev *Actual Flow Design Flow V10 % Full
(ft) (cfs) (cfs) (fps)
241 .85 38 .28 6 .1 77.9
242 .90 31 .01 5.2 74 .2
100 year storm
Travel T ime , Im *Actual Flow Des ign Flow V100 % Full
Travel Time, tnoo
(sec) (min) (cfs) (cfs) (fps) (sec) (min)
41 0 .68 51 .6 5 6 .6 9 7 .1 38 0 .63 ------------
14 0.23 41 .86 5 .7 92.4 13 0 .21
---· -----------·-
3 3x2 165 .3 0.40 243 .83 243 .17 22 .37 5.4 69.2 31 0 .5 1 30.45 5.8
------
4 27 34.4 0 .45 244 .05 243 .90 14 .72 5 .3 65.4 6 0 .11 19 .85 5 .5 -----I-------
5 24 31 .2 0 .55 244.47 244 .30 7.4 1 11 .97 5 .5 65 .7 6 0 .0 9 9 .99 16 .13
*The se values reflect the actual fl ow for the 18" & 24" pipes . The design fl ow for the se pipe si zes reflects a 25% reduction 1n pipe area .
(Ref er to at ta ched calculation for specific information .)
5 .6
87.2 29 0.48
---------
84 .8 6 0.10 ------f---·--·-
8 5 .6 6 0.09
City of College Station requirement to Reduce Cross-Sectional Area of 18" & 24" Pipes by 25%
Using Mannings Equation from page 48 of the College Station Drainage Policy & Design Standards Manual :
Q = 1.49/n * A * R213 * S 112
Q = Flow Capacity (cfs)
18" Pipe :
Pipe size (inches) =
Wetted Perimeter WP, (ft)=
Cross-Sectional Area A, (ft2) =
Reduced Area A R, (ft2 ) =
Hydraulic Radius R = A/W P· (ft) =
Reduced Hydr Radius R R = A R/WP· (ft) =
Roughness Coefficient n =
Friction Slope of Conduit Sr. (ft/ft) =
Example Calculation :
Slope Flow Capacity Reduced Flow Capacity
s Q
0 .005 6 .91 -----0 .006 7 .57 ---
0 .007 8 .18
24" Pipe:
Pipe size (inches) =
Wetted Perimeter WP, (ft)=
Cross-Sectional Area A , (ft2) =
Reduced Area AR , (W) =
O reduced
4 .28
4 .69
5 .06
Hydraulic Radius R = A/WP· (ft) =
Reduced Hydr Radius RR = AR/WP • (ft) =
Roughness Coefficient n =
Friction Slope of Conduit S r. (ft/ft)=
Example Calculation:
Slope Flow Capaci ty Reduced Flow Capa city
s Q Oreduced
0 .005 14 .89 9.22 ----0 .006 16 .31 10 .1 ---------------
0 .007 17 .61 10.9
Conclusion :
8
4 .71
1. 766
1 . 325
0. 375
0. 281
0 . 014
0 .01
% Diff erence
Ored uc ed /Q
0.6 19
0.6 19
0.6 19
2 4
6 .28
3 .14
2. 355
0 .5
0 . 375
0 . 014
0 .01
% Difference
Multiply actual Q in 18" & 24" pipes by 1.615 to reflect a 25% reduction in the
cros s-sectional a rea ca lled for on page 4 7 , paragraph 5 of th e College Station
Drain age Po li cy & Design Standards manual.
North Forest Subdivision
Pipe Flow Diagram
0 10 (cfs)
Inlet 5 I 7.41 I
J,
Pipe 5 I 7.41
J,
Inlet 4 I 7 .31
J,
Pipe 4 I 14 .72
J,
In let 3 I 7.65
J,
Box 3 I 22 .37
J,
Inlet 2 I 8 .64
J,
Box 2 ! 31 .0 1 I
J,
Inl et 1 I 7.27
J,
Box 1 I 38 .28
J,
II Existin g C hann el II
North Fo rest Subdivision
Pipe Flow Diagram
0 100 (cfs)
Inlet 5 I 9 .99
J,
Pipe 5 I 9 .99
J,
Inlet 4 I 9 .86
J,
Pipe 4 I 19 .85
J,
Inlet 3 I 10 .60
J,
Box 3 I 30 .45
J,
Inlet 2 I 11 .4 1
J,
Box 2 I 4 1.86
J,
Inlet 1 I 9 .79
J,
Bo x 1 I 51 .65
J,
II Existi ng Chann el JI
Given Input Data:
Box 1 -10 Year Storm
Manning Pipe Calculator
S hape .......................... .
Solvi ng for .................... .
Height ......................... .
Widt h .......................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Computed Resu lts:
Depth ......................... ,. .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hy draulic Radius ............... .
Percent Ful 1 ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Given Input Data :
Box 1 -100 Year Storm
Manning Pipe Calculator
Shape .......................... .
Solving for .................... .
Height ......................... .
Width .......................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Computed Results:
Depth .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Ve locity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full fl ow Flowrate ............. .
Full flow velocity ............. .
North Forest Su bdlv l slon
Co I I ege Stati on , Texas
Rect angu lar
Depth of Fl ow
24.0000 in
4 8.0000 in
38.2800 cfs
0.0 040 ft/ft
0. 0140
18.6 907 i n
8 .0000 ft2
6.2302 ft2
85 .3813 in
144 .00 00 in
6.144 2 fps
10.507 6 in
77.8777 %
40.9842 cfs
5.1230 fps
Rectangular
Depth of Flow
24.0000 in
48.0000 in
51.6500 cfs
0.00 40 ft/ft
0. 0140
23.3093 in
8 .0000 ft2
7.7698 ft2
94.6186 in
144 .0000 in
6.647 6 fps
11.8 24 8 in
97.1 220 %
40.9842 cfs
5 .1230 fps
Gi ven Input Data:
Box 2 -10 Year Storm
Manning Pipe Calculator
Shape .......................... .
So lving for .................... .
Height ......................... .
Wi dth .......................... .
Flowrat e ....................... .
S lope .............. · ............ .
Manning's n .................... .
Com puted Results:
Depth ......................... , .
Area ........................... .
Wetted Are a .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Re ctangular
Depth of Flow
24.0000 in
48 .00 00 in
31.0100 cfs
0 .0030 ft/ft
0 .0140
17 .8070 in
8 .0000 ft2
5.9357 ft2
83 .614 0 in
144 .00 00 in
5 .2244 fps
10.2224 in
74 .1958 %
35.4934 cfs
4.4367 fps
Box 2 -100 Year Storm
Manning Pipe Calculator
Given Input Data :
Shape .......................... .
Solving for .................... .
Height ......................... .
Width .......................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Computed Results :
Dept h .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radi u s ............... .
Percent Full ................... .
Full fl ow Fl o wrate ............. .
Full flow veloci t y ............. .
North Fo r est Subdiv i s i o n
College Sta ion, l'e;-:as
Rectangular
Depth of Flow
24.0000 in
48 .0000 in
41.8600 cfs
0.0030 ft/ft
0 .0140
22.1857 in
8.0000 ft2
7.3952 ft2
92.3713 in
144 .0000 in
5.6604 fps
11.5286 in
92.4402 %
35.4934 cfs
4.4367 fps
Gi v en Input Data:
Box 3 -10 Year Storm
Manning Pipe Calculato r
Shape .......................... .
Solving for .................... .
Height ......................... .
Width .......................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Computed Result s:
Depth ........................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Rectangular
Depth of Flow
24.0000 in
36 .0 000 in
22.3700 cfs
0 .0040 ft /ft
0.0140
16.5985 in
6.0000 ft2
4.1496 ft2
69.1971 in
120 .0 000 in
5 .39 08 fps
8.6354 in
69.1606 %
28 .6532 cfs
4.7755 fps
Box 3 -100 Year Storm
Manning Pipe Calculator
Given Input Data :
Shape .......................... .
Solving for .................... .
Height ......................... .
Width .......................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Computed Results :
Depth .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radiu s ............... .
Percent Full ................... .
Full flow Flowrat e ............. .
Full fl ow v elocit y ............. .
No rth Forest S ubd iv i si o n
Co l leg e Stat io 11, Te >:c'"'
Rectangular
Depth of Flow
24.0000 in
36.0000 in
30 .4500 cfs
0.0040 ft/ft
0.0140
20.9388 in
6.0000 ft2
5.2347 ft2
77.8777 in
120.0000 in
5.8169 fps
9.6793 in
87 .2 452 %
28.6532 cfs
4.7 755 fps
Pipe 4 -10 Year Storm
Manning Pipe Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Diameter ....................... .
Flowrate ....................... .
Slope .......................... .
Manning' s n .................... .
Computed Results:
Depth .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Circular
Depth of Flow
27.0000 in
14 .7200 cfs
0.0045 ft/ft
0.0140
17.6578 in
3 .9 761 ft2
2.7551 ft2
50 .8644 in
84.8230 in
5.3428 fps
7.7999 in
65.3991 %
19.2915 cfs
4.8519 fps
Pipe 4 -100 Year Storm
Manning Pipe Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Diameter ....................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Computed Results :
Depth .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
No rth Fo r est S ubdi v ision
Colleg e S ati o n, Te;-:a,;
Circular
Depth of Flow
27.0000 in
19.8500 cfs
0.0045 ft/ft
0. 0140
22.9057 in
3.9761 ft2
3 .5961 ft2
63.2234 in
· 84 .8230 in
5.5198 fps
8.1907 in
84.8359 %
19.2915 cfs
4.8519 fps
Pipe 5 -10 Year Storm
Manning Pipe Calculator
Gi ven Input Data:
Shape .......................... .
Solving for .................... .
Diameter ....................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Computed Results :
Depth .......................... .
Area ......................... ·. ·
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
Circ ular
Depth of Flow
24.0000 in
11 .9700 cfs
0.0055 ft/ft
0 .0140
15.7730 in
3 .1416 ft2
2.1891 ft2
45.3754 in
75 .3 982 in
5.4680 fps
6.9472 in
65.7210 %
15.5788 cfs
4.9589 fps
Pipe 5 -100 Year Storm
Manning Pipe Calculator
Given Input Data:
Shape .......................... .
Solving for .................... .
Diameter ....................... .
Flowrate ....................... .
Slope .......................... .
Manning's n .................... .
Computed Results:
Depth .......................... .
Area ........................... .
Wetted Area .................... .
Wetted Perimeter ............... .
Perimeter ...................... .
Velocity ....................... .
Hydraulic Radius ............... .
Percent Full ................... .
Full flow Flowrate ............. .
Full flow velocity ............. .
No r th Porest S ubdi v is i on
Col I e e Sta · i o n , Te;-:c1 ~;
Circular
Depth of Flow
24.0000 in
16 . 1300 cfs
0.0055 ft/ft
0. 0140
20.5340 in
3.1416 ft2
2 .8619 ft2
56.6870 in
75.3982 in
5.6361 fps
7 .2 700 in
85.5585 %
15 .5788 cfs
4.9589 fps
EXHIBIT A
Pre-Development Drainage Area Map
2-l