HomeMy WebLinkAboutDrainage DesignASH & BROWNE ENGINEERING, INC.
Engineers and Consultants
P.O. Box 10838, College Station, Texas 77842
979-846-6914 877-245-4839 Fax:979-846-8914
February 26, 2003
Spencer Thompson
Development Services
City of College Station
P.O. Box 9960
College Station, Texas 77842
Re.: Drainage Design for the City Limits Restaurant
Fedora Subdivision, College Station, Texas
ABEI # 1051001
Dear Mr. Thompson:
This letter summarizes the drainage design for the Fedora Subdivision (The City Limits
Restaurant) on Wellborn Road in Southwest College Station.
GENERAL LOCATION AND DESCRIPTION
Location
The Fedora Subdivision consists of a 1.128 acre tract of land, lying and being situated in
the Robert Stevenson League, Abstract No. 54 in the City of College Station. The property
is adjacent to Wellborn Road and the abandoned Graham Road right of way. The
Edelweiss Business Center surrounds the subject property on two (2) sides.
Description of Property
There are no drainage ways or tributaries within or adjacent to the subject property. The
property is crowned in the center producing 4 drainage basins, A, B, C & D (See
Attachments). The storm water run-off from the basins is conveyed to the North Fork of
the Lick Creek Drainage Basin via sheet flows across adjoining properties and the
Wellborn Road drainage ditches. The property is located in the unshaded Flood Zones
' X', outside the 500-Yr. flood plain, as shown on FIRM (Flood Insurance Rate Map) map,
Map Number: 48041 C0182 C, effective date of July 2, 1992.
Runoff Calculation Method
Runoff for all areas was calculated based on the "Rational Method". The runoff
coefficients of 0.4, 0.5 and 0.75 were used for natural grassland areas, gravel -grass mix,
and the developed areas, respectively. Intensity was determined by using the calculated
time of concentration for each drainage area. As a result of the drainage areas being of
minimal size, the Time of Concentration (Tc) was less than the required minimum standard
of 10 minutes as lined out in the City of College Station's Drainage Requirements.
Hydraulic Calculations
As shown in Table 1.1 and Table 1.2, detention facilities were required for Basins B and
D. Weirs (curb cuts) were utilized to meter the release of the increased storm water
production. The weirs were hydraulically modeled using the weir equation, Q=C„, * L * Hex'
and the Hydraflow software 'Hydrographs 6.02' for Basins B & D for crest lengths of 9" for
both. The stage discharge curves for both weirs are attached for your review.
DRAINAGE FACILITY DESIGN
General Concept
Once the site is developed, the majority of the site will consist of a parking area and a
proposed restaurant building. A majority of the run-off will be captured in the parking
areas and released via curb cuts in Basins B and D. Basins A and C did not incur any
increases in storm water production due to the development.
The following table illustrates the existing and proposed runoff for the project site and the
flow increase/decrease for the drainage basins:
Table 1.1
Existing/Proposed Runoff
Existing Runoff
Proposed Runoff w/o
Increase/Decrease
(cfs)
Detention
(cfs)
(cfs)
Storm Frequency (yr)
Storm Frequency (yr)
Storm Frequency (yr)
5
10
25
50
100
5
1 10
1 25
1 50
100
5
10
25
1 50
1 100
Basin
0.54
0.60
0.69
0.77
0.81
0.54
0.60
0.69 1
0.77
0.81
0.00
0.00
0.00
0.00
0.00
A
Basin
0.76
0.85
0.98
1.10
1.15
1.43
1.59
1.83
2.06
2.15
0.67
0.74
0.86
0.96
1.00
B
Basin
1.14
1.27
1.47
1.64
1.72
0.58
0.65
0.74
0.83
0.87
(0.6)
(0.6)
(0.7)
(0.8)
(0.8)
c
Basin
1.14
1.28
1.47
1.65
1.72
2.14
2.39
2.75
3.09
3.23
1.00
1.12
1.29
1.44
0.00
D
Notes: If flow increase is greater than 0.5 cfs
detention is required.
Based on the above information, the project site requires detention in Basins B & D. This
will be facilitated by storing run-off in the parking lot areas and controlling the release of
run-off out of the parking lot areas via curb cuts located in Basins B & D. The metered
outfalls plus the remaining surface run-off of the landscape areas and the remaining
building areas will be less than the pre -developed run-off conditions.
Table 1.2
Existing/Proposed Runoff with Detention Facility
Existing Runoff
Proposed Runoff
Increase/Decrease
(cfs)
w/Detention
(cfs)
(cfs)
Storm Frequency (yr)
Storm Frequency (yr)
Storm Frequency (yr)
5
10
25
50
100
5
1.10
25
50
100
5
10
25
50
100
Basin
0.54
0.60
0.69
0.77
0.81
Detention Not Necessary
(0.5)
(0.6)
(0.7)
(0.8)
(0.8)
A
Bas in
0.76
0.85
0.98
1.10
1.15
0.76
0.83
0.92
1.00
1.13
0.0
0.0
(0.1)
(0.1)
0.0
B
Basin
1.14
1.27
1.47
1.64
1.72
Detention
Not Necessary
(1.1)
(1.3)
(1.5)
(1.6)
(1.7)
C
Basin
1.14
1.28
1.47
1.65
1.72
1.08
1.18
1.31 1.44
1.48
(0.1)
(0.1)
(0.2)
(0.2)
(0.2)
D
Notes: If Flow increase is less than 0.5 cfs, the impact on the downstream flow path is considered to be negligible.
Compliance with City Standards
From the information that is presented in this report, we have shown that the development
of this site will meet the City's policy.
Sincerely,
ASH &,BROWNE ENGINEERING, INC.
attis, P.E.
Engineer
.. '
JOE I. GATTIS
.............I
!.% . 90964
PRE—DEV BASIN 'A'
AREA = 0.139 AC
Q(25)r.) = 0.69 cfs
Q(100yr.) = 0.81 cfa PRE—DEV. BASIN 'B'
C = 0.5 AREA = 0.247 AC
(SHEET FLOW) Q(25yr.) = 0.98 cfs
(SHEET FLOW) Q(100 yr.) - 1.15 cfs
i C=0.4
EDELWEISS
BUSINESS
EDELWEISS ; ' ' CENTER
BUSINESS , i i , , (SHEET FLOW)
CENTER
(SHEET FLOW)
(SHEET FLOW)
��
—✓ PRE=DEV BASIN V
(SH
I OW)
AREA - 0.370 AC
Q(25yr.) = 1.47 cfs
�q \
Q(100yr.) = 1.72 cfs
PRE—
EV BASIN 'D'
EDELWEISS C = 0.4
AREA
0.371 AC
\�
BUSINESS
Q(25yr.)-
1.47 cfs
CEN TER
= M 2 cfs
\
C — 0.4
U� —
(SHEET FLOW)
Q
�OF
%•••••••e,: *�) ATTACHMENT##1
,E1.GATTIS " D PRE -DEVELOPED DRAINAGE
•••••••••••••� BASINS
90964 a 9 e®
•iii•:••• SCALE: 1" = 20'
'IONALEN ASH EA.&. Ed Cb.EWmm 6, INC.
0�'_� y0' Cngiomrs and ConsWtmis
P.O. Box 10838, College Station. Te 77842
�.... 1051001-003-01 979�46G914 B]7d4t-1639 Faa: 979-646-8914
DEVELOPED BASIN 'A'
AREA = 0.139 AC
Q(25)r.) = 0.69 cfs
Q(100yr.) = 0.81 cfs
C = 0.5
EDELWEISS
BUSINESS CENTER
DEVELOPED BASIN IX
AREA = 0.615 AC
Q(25yr.) = 4.56 cfs
Q(100yr.) =5.35 cfs
C = 0.75
9" WIDE CURB OUTFALL
TO DITCH FLOW LINE
OF
000
JOE I. GATTIS
r..... a....•
. 90J64 _ J
/ EDELWEISS
BUSINESS CENTER
DEVELOPED BASIN 'B'
AREA = 0.275 AC \
Q(25yr.) - 2.04 cfs
Q(100)r.) = 2.39 cfs
C = 0.75
9" WIDE CURB OUTLET
SHEET FLOW OUTFALL
(SHEET FLOW)
(SHEET FLOW)
/ DEVELOPED BASIN 'C'
AREA = 0.10 AC
Q(25yr.) = 0.74 cfs
Q(100yr.) = 0.87 cfs
C = 0.75
EDELWEISS
BUSINESS CENTER
GRASS BERM
3'wx6"Ht.
AATTACHMENT#2
B DEVELOPED DRAINAGE
BASINS
SCALE: 1" = 20' ASH & EROMYE ENGINEERING, INC.
0 5' 10, 2C Hnginmm and ConsWlems
1:77=mmmc=� P.O. Box 10838, College Station, Texas 77842
1051001-003-02 1
979-8466914 877-245-0839 Pat: 979E-068914
DEVELOPED BASIN 'A'
AREA = 0.139 AC
0(25)r.) = 0.69 cfs
Q(100yr.) = 0.81 cfs
C = 0.5
EDELWEISS
BUSINESS CENTER
DEVELOPED BASIN 'N
AREA = 0.615 AC
Q(25yr.) = 4.56 cfs
0(100yr.) =5.35 cfs
C = 0.75
9" WADE CURB OUTFALL
TO DITCH FLOW LINE
JOE 1. GATTIS
1.".........
.90964 _r
\
/ EDELWEISS
BUSINESS CENTER
DEVELOPED BASIN 'B'
AREA = 0.275 AC \
Q(25yr.) - 2.04 cfs
Q(100yr.) = 2.39 cfs
C = 0.75
9' WIDE CURB OUTLET
SHEET FLOW OUTFALL
(SHEET FLOW)
(SHEET FLOW)
/
DEVELOPED BASIN 'C'
AREA = 0 AC
—
=
Q 25yr.) = 0.74 cfs
Q 100yr.) = 0.87 cfs
C = 0.75
EDELWEISS
BUSINESS CENTER
GRASS BERM
3'w x 6" Ht.
AATTACHMENT#2
s DEVELOPED DRAINAGE
BASINS
SCALE: 1" = 20' ASH & BROWIYE ENGINEERING, INC.
0 5' 10, 20' Engin. and C"aaallaata
P.O. Box 10838, College Station, Texas 77842
1051001-003-02 1
979-846-6914 877-245-4839 Fax:979-8468914
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