HomeMy WebLinkAboutDrainage Report Addendum 3Addendum 3 to
Drainage Report
for
The Barracks Subdivision
Phase 2
College Station, Texas
May,2010
Engineer:
SCHULTZ ENGINEERING, LLC
TBPE Firm Registration No. 12327
P.O. Box 11995
College Station, TX 77842
(979) 764-3900
Developer:
Greens Prairie Investors, Ltd.
4490 Castlegate Drive
College Station, Texas 77845
(979) 690-7250
GENERAL
CONCLUSION
Addendum No. 3 to
Drainage Report
The Barracks Subdivision -Phase 2
May,2010
This addendum is issued to address proposed modifications to 2 existing curb
inlets, one on Sergeant Drive and one on Lieutenant Avenue at the Barracks
Subdivision. The inlets are being moved to accommodate the driveways for the
townhomes. The existing inlets would block a significant portion of the proposed
driveway and it is a concern that vehicles would back over the curb inlets from the
driveway and damage the inlet and/or the vehicle. Inlet 121 on Sergeant Drive will
be shortened from 10' to 5'. The calculations shown on Exhibit C shows there will
be a small amount of bypass flow that will go to Inlet 120. Also on Exhibit C are
the inlet in sump calculations which show Inlet 120 can handle the small increase
in flow due to the bypass flow. Inlet 130 is to be shortened to 8.5' from 10'. The
calculations show that the depth of water at the inlet opening will be 3.77" for the
10 year and 4. 76" for the I 00 year storm. Exhibit A is the Drainage Area Map,
Exhibit B is the Drainage Area Summary, and Exhibit D is the Gutter Depth Check
Summary.
The inlet modifications proposed on the construction drawing, Sheet I of 1, for
The Barracks Subdivision will function as originally designed and are in
accordance with the BCS Unified Design Guidelines.
f-#=-( 'l J 2 7
...,. ...
,, .. ... ., ....... .....
THE BARRACKS SUBDIVISION
INLET MODIFICATION PHASE 2
COLLEGE STATION, TEXAS MAY 2010
120
SCHULTZ ENGINEERING LLC nus BO.um or PllORSSIOKAL lllGlllDllS 1'11111 IDGIS'l'llATIOft 1(0. laz?
&'730 l.oacmJre, llult.o A
COUICI ft!TIOI(, nus 771146
979.?M.a-
60 0 120
SCALE IN FEET
ALLEY 2
' > ,--C. \ ~ I I I I ~ I
' ' I I I ____ _,.
---1
L00.:.2 1 ----, __ J
DRAINAGE AREA MAP EXHIBIT A
Exhibit 8
The Barracks Subdivision -Phase 2 -Inlet Modification -May 2010
Drainage Area Summary
Area, A c ~ 10 year storm 100 year storm
Area#
(acres)
120 0.408
-----~ ------
121 0.097 ---·-122 0.966
131 0.688
0~ 0.109
C4UID 0.632
140C 0.620
141 0.654
142 0.986
143 1.152
144 1.107 -
145 0.839
210 0.759
220 0.666
320 0.158
330 0.617
The Rational Method:
Q=CIA
Q = Flow (cfs)
A= Area (acres)
C = Runoff Coeff.
I = Rainfall Intensity (in/hr)
Brazos County:
110 010
(min) (in/hr) (cfs)
0.69 10 8.635 2.43
0.69
-..,---f> ..
1Q 8.635 0.58 --·
0.69 10 8.635 5.76
0.69 10 8.635 4.10
0.69 10 ----i-,,Q.59<; 8.635 --l_ --0.69 10 8.635 __,,
-.r.rr
0.69 10 8.635 3.69
0.69 10 8.635 3.90
0.69 10 8.635 5.87
0.69 10 8.635 6.86
0.69 10 8.635 6.60
0.69 10 8.635 5.00
0.69 10 8.635 4.52
0.69 10 8.635 3.97
0.69 10 8.635 0.94
0.69 10 8.635 3.68
I
I
I = b I (tc+d)•
tc = Time of concentration (min)
10 vear storm
b = 80
d = 8.5
e = 0.763
100 year storm
b = 96
d = 8.0
e = 0.730
1100
(in/hr)
11 .639
11 .639
11 .639
1j...63~
11.639
11 .639
11 .639
11 .639
11.639
11 .639
11 .639
11 .639
11 .639
11 .639
11 .639
11.639
0100
(cfs)
3.28
0.78
7.IS--
5.53
/D.88" v--
\._ <; nA /
4.98
5.25
7.92
9.25
8.89
6.74
6.10
5.35
1.27
4.96
le = L/(V*60)
L = Length (ft
V = Velocity (fUsec)
..
Exhibit C
The Barracks Subdivision -Phase 2 -Inlet Modifications -May 2010
Storm Sewer Inlets on Grade -Design Analysis
Inlet
No.
121
Length
ft.
5
Street
Slope,%
0.80%
010
cf s
0.58
The Barracks Subdivision -Phase 2
L10, ft
Design
5.46
Bypass
cf s
0.01
0100
cf s
0.78
Storm Sewer Inlets in Sump -Design Analysis
Inlet Length 010 D10 D10
No. ft. cf s ft in
120 5 2.44* 0.32 3.84 3.32* 0.393
130 8.5 4.55* 0.314 3.77 ~0.397
L100. ft
Design
4.72
-1.s-1
4.76
~
Bypass
cf s
0.04
rl
\.'<
f ,5i,
-fril
*Includes bypass flow from upstream inlets on grade ~
, .. . '
Exhibit D
The Barracks Subdivision
Phase 2 -Inlet Modifications -May 2010
Depth of Flow in Gutter
(Refer to Exhibit A for Gutter Locations)
Gutter A
Location c Area# (acres)
130 • N 140A 0.109 0.69
130 -s 1408 0.632 0.69
-120 120 0.408 0.69 ----
Slope le 1,.
(ft/ft) (min) (In/hr)
0.0072 10.0 8.635
0.0073 10.0 8.635
0.0080 10.0 8.635
Sergeant Drive & Lieutenant Avenue. Laydown Curb . Hl-yr storm max design depth . 4"
Transverse (Crown) slope (fVftl
27' street= 0.0330
38' street= 0.0315
Straight Crown Flow !Solved to find actual depth of flow in gutter, vi:
Q = 0.56 • (zlnl • s1'2 • v•JJ c> v ={QI [0.56 • (zln) • S112J}311
n = Roughness Coefficient = 0.018
S = StreeVGutter Slope (ft/ft)
y = Depth of flow at inlet (ft)
z = Reciprocal of crown slope:
27' street = 30
38' street = 32
10-year storm 100-year storm
a,. Y1o.actu., 1100 a, .. Y100
(cfs) (ft) (In) (In/hr) (cfs) (ft) (In)
0.65 0.164 1.97 11.639 0.88 0.184 2.21 v 3.77 0.317 3.80 11 .639 5.08 0.355 4.26 ~
~
2.44 0.265 3.18 11 .639 fi.3v' 0.297 3.57
...........