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JUN 1 8 200
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~~~~ Ofc: 979 .693.5359 Fax: 979.693.4243 Email: mdgcs@mdgcs.com Web: www.mdgcs.com
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TABLE OF CONTENTS
1.0 PROJECT SCOPE ..................................................................................................... 4
1.1 SITE LOCATION ........................................................................................................ 4
1.2 GENERAL DESCRIPTION ......................................................................................... 4
2.0 DRAINAGE BASINS & SUB-BASINS ................................................................... .4
2.1 MAJOR DRAINAGE BASIN DESCRIPTIONS ........................................................ .4
2.2 SUB-DRAINAGE BASIN DESCRIPTIONS .............................................................. 5
3.0 DRAINAGE DESIGN CRITERIA & CONSTRAINTS ......................................... 5
3.1 OPEN CHANNELS ...................................................................................................... 5
3.2 DETENTION FACILITIES ......................................................................................... 6
4.0 DRAINAGE SYSTEM MODELING ....................................................................... 6
4.1 OPEN CHANNELS ...................................................................................................... 7
4.2 DETENTION FACILITIES ......................................................................................... 7
5.0 CONCLUDED DRAINAGE IMPROVEMENTS ................................................... 7
5.1 OPEN CHANNELS ...................................................................................................... 7
5.2 DETENTION FACILITIES ......................................................................................... 8
APPENDIX A -HYDRAULIC COMPUTATIONS
APPENDIX B -MAPPING
LIST OF TABLES
DESCRIPTION PAGE NO.
TABLE #1: PILOT CHANNEL FLOW RESULTS ........................................................... 8
TABLE #2: DETENTION POND VOLUME RESULTS ................................................... 8
TABLE#3: WEIRFLOWRESULTS ................................................................................. 9
TABLE #4: STAGE/STORAGE RESULTS ...................................................................... 9
Planters & Merchants State Bank
Site, Grading, Drainage & Utility Improvements Municipal Development Group
1.0 PROJECT SCOPE
This report outlines the pavmg and drainage improvements for the proposed
Planters & Merchants State Bank development at the Dartmouth Addition
Subdivision (Block One, Lot 1 ). This drainage report will consist of the
requirements necessary for the improvements of this site in accordance with the
provisions of the City of College Station Drainage Policy and Design Standards.
Previous drainage studies have been performed on the adjacent properties and this
property's watershed, but none have considered post-development conditions on
the subject property.
1.1 SITE LOCATION
The project is located on the south side of Southwest Parkway
approximately 2,000 linear feet east from the intersection with Texas
Avenue. The site is adjacent to Ashford Square to the west and the
Heritage Apartments to the south. The east adjacent property is vacant and
unimproved, but an Exxon convenience store is planned.
1.2 GENERAL DESCRJPTION
The subject property is currently vacant. This land generally slopes to an
unnamed tributary of Bee Creek at a grade of approximately 2.00%. This
site is currently unimproved with native grasses, and weeds. Runoff drains
south over land to the unnamed tributary thence to Bee Creek being a
secondary drainage system. Bee Creek drains to the Carter's Creek
drainage basin.
2.0 DRAINAGE BASINS & SUB-BASINS
2.1 MAJOR DRAINAGE BASIN DESCRJPTIONS
The paving and drainage improvements project site is contained within the
Bee VII Sub-basin contained within the drainage-watershed of the Bee
Creek Drainage System, part of the Carter's Creek Drainage Basin. This
drainage basin is illustrated on Exhibit #1 -"Carter's Creek Drainage
000761-3357 Drainage Report Final Drainage Report -4
Planters & Merchants State Bank
Site, Grading, Drainage & Utility Improvements Municipal Development Group
Basin" located in Appendix B -Mapping. The borders of this drainage
basin roughly consist of Rock Prairie Road on the south and west, State
Hwy No 30 to the east, and State Hwy No. 21 to the north.
2.2 SUB-DRAINAGE BASIN DESCRIPTIONS
This projects sub-drainage basin consists solely of the 2.02 acre tract. A
graphical representation of the sub-drainage basin is illustrated on Exhibit
#2 -"Sub-Drainage Basin" located in Appendix B -Mapping.
No portion of this project is located within the 100-year floodplain as
graphically depicted by F.E.M.A FIRM Community Panel No
48041C0144 C (as revised by LOMR dated July 10, 2000) and Panel No.
48041C0163 C), having an effective date of July 2, 1992. An excerpt of
the FIRM map with the location of the project site is illustrated on Exhibit
#3 -"FIRM Map" located in Appendix B -Mapping
3.0 DRAINAGE DESIGN CRITERIA & CONSTRAINTS
For all development within the City of College Station, there are criteria on the
use of which design storms and development conditions for type of drainage
improvements. Below, in each type of improvement, the required design
constraints are more fully detailed. All drainage improvements shall also be
analyzed during the 100-year rainfall event to insure that no adverse conditions
will exist.
3.1 OPEN CHANNELS
Open channel improvements shall be designed in accordance to the City of
College Station's Drainage Policy and Design Standards. Unless
otherwise stated, the following constraints shall dictate the design of all
open channels:
•!• Minimum grade shall be 0.4% for earth or vegetative lined channels.
000761-3357 Drainage Report Final Drainage Report - 5
Planters & Merchants State Bank
Site. Grading, Drainage & Utility Improvements Municipal Development Group
•:• Channel capacities shall be dictated by the design storm of the 25-year
rainfall event.
•:• Low-flow pilot channels shall be required for grass-lined channels
with a carrying capacity of 1/3 of the peak discharge of the 5-year
rainfall event.
•:• Minimum permissible velocity of 2.5 ft/sec during the 25-year rainfall
event.
•:• Maximum channel velocities shall be as dictated below:
> Exposed earth at 3.0 ft/sec.
> Seeded grass at 4.5 ft/sec.
> Sodded grass at 6.0 ft/sec.
> Impermeable surface at 10 ft/sec.
•:• Maximum side slope for grass-lined earth channel is 3: 1.
•:• Channels with trapezoidal cross-section shall have a minimum bottom
width of 4 feet.
•:• Channel shall have a minimum freeboard of 0.5 feet.
•!• The 100-year rainfall event shall be contained within the channel
drainage easement.
•:• Minimum drainage easement width shall be the channel's top width
plus 20 feet.
3.2 DETENTION FACILITIES
Detention shall be designed in accordance to the City of College Station's
Drainage Policy and Design Standards. Unless otherwise stated, the
following constraints shall dictate the design of detention basins:
•!• Detention facilities shall have the capacity to contain the 100-year
rainfall event.
•!• Maximum detention basin's side slope shall be 4:1 with vegetative
cover and 2: 1 for non-vegetative cover.
•:• Bottom slopes of the detention basin with vegetative cover shall be at a
grade of 20: 1 with low-flow pilot channels.
•!• Minimum of 0.5 feet of free board during the 100-year rainfall event.
•!• Detention facilities other than parking lots and rooftops shall have an
increased capacity of 10% to allow for sedimentation.
4.0 DRAINAGE SYSTEM MODELING
For all drainage system modeling, the volume of runoff will be calculated. The
drainage area calculations are summarized accordingly using the Rational
Method: (Q=CIA) where "Q" is the runoff in cubic feet/second, "C" is the runoff
000761 -3357 Drainage Report Final Drainage Report -6
Planters & Merchants State Bank
Site, Grading, Drainage & Utility Improvements Municipal Development Group
coefficient, "I" is the storm intensity in inches/hour for each selected frequency,
and "A" is the drainage area in acres. A minimum 10-minute time of
concentration for all calculations will be assumed. The selected frequencies will
be 2, 5, 10, 25 , 50, 100-year rainfall events.
4.1 OPEN CHANNELS
Open channel hydraulic calculations are aided by the program FlowMaster
v. 5.7 by Haestad Methods. Within this program, basic geometry and
characteristics of a proposed or existing channel can be defined. From this
information, Manning 's formula is then used to calculate desired
parameters of the open channel.
4.2 DETENTION FACILITIES
Detention requirements are determined by graphical means. Tabulations of
the pre-development and the post-development hydrographs of the
drainage areas are provided. The hydrographs are based on the standard
SCS unit hydrograph with time to peak discharge set to equal the time of
concentration and the total base time set at 3.00 times the time of
concentration.
5.0 CONCLUDED DRAINAGE IMPROVEMENTS
The proposed development receives runoff from the primary sub-drainage basin (see
Exhibit #2). Using these calculated runoff values, the drainage structures and detention
facilities were design and checked for compliance with the drainage policy.
5.1 OPEN CHANNELS
Within the detention facility is a pilot channel that will accommodate for
low-flow between the proposed parking lot and the discharge weir.
Additionally, there is a pilot channel on the downstream end of the
discharge weir that will carry flow to the existing drainage channel. The
pilot channel upstream on the weir was designed for post-development
000761-3357 Drainage Report Final Drainage Report -7
Planters & Merchants State Bank
Site, Grading, Drainage & Utility Improvements Municipal Development Group
conditions. The open-channel and concrete pilot channel downstream of
the weir was designed at pre-development conditions since the weir will
restrict the flow to that discharge amount. Actual designed hydraulic
values are illustrated below in Table # 1.
TABLE #1
PILOT CHANNEL FLOW RESULTS
1/3
5-YEAR CHANNEL ..
.CONDITION Q SLOPE WIDTH VELOCITY
(cfs) (%) (ft) (fps)
PRE 3.98 2.50 3.23 6.1
POST 1.98 10.00 1.92 8.61
The downstream pilot channel exceeds normal constraints for open-
channel design. In order to prevent erosion and scouring of the channel, it
will be lined with riprap (see Exhibit #2).
5.2 DETENTION
The detention facility size was based from the comparisons of the existing
runoff conditions and the proposed runoff conditions. Based from the pre-
development and post-development hydrographs the required detention
volumes is as follows:
TABLE#2
DETENTION POND VOLUME RESULTS
FREQUENCY PRE~Q POST-Q VOCOME-
(yr) (cfs) (cfs) (ft3)
2 4.90 9.82 4429
5 5.95 11 .94 5385
10 6.68 13.40 6045
25 7.63 15.30 6903
50 8.63 17.30 7804
100 9.01 18.06 8148
000761-3357 Drainage Report Final Drainage Report - 8
Planters & Merchants State Bank
Site, Grading, Drainage & Utility Improvements Municipal Development Group
The weir structure for the outlet of the detention pond was designed so that the
design discharge will be equal to or less than the pre-development flow rates. The
comparison of allowable and actual discharge rates are as follows:
TABLE#3
WIER FLOW RESULTS
ALLOWABLE
FREQUENCY DISCHARGE
(yr) (cfs)
2
5
10
25
50
100
4.90
5.95
6.68
7.63
8.63
9.01
.ACTUAL
DISCHARGE
(cfs)
3.29
4.54
5.54
6.83
8.38
9.01
For clarity, Table #4 illustrates the staging of the detention pond. Each event
represented is a peak conditions.
TABLE #4
ST AGE/STORAGE RESULTS
VOLUME IN
FREQUENCY POND DEPTH
(yr) (ft3) (ft)
2 4429 0.64
5 5385 0.78
10 6045 0.88
25 6903 1.00
50 7804 1.13
100 8148 1.18
000761-3357 Drainage Report Final Drainage Report -9
000761-3357 Drainage Report.doc
APPENDIX A
HYDRAULIC COMPUTATION
DESCRIPTION
APPENDIX A
TABLE OF CONTENTS
PAGE NO.
Drainage Calculations ................................................................................................. A-1
Open Channel Calculations ......................................................................................... A-2
Weir Calculations ........................................................................................................ A-3
000761-3357 Drainage Report.doc
PRE-DEVELOPMENT
GENERAL INFORMATION
Description: Drainage area of site before development.
Drainage Area (APRE) = 2.020 acres
TIME OF CONCENTRATION CTc)
GIVEN
Maximum Travel Distance (DPRE)
Velocity of Runoff (VPRE) =
440 ft
ft 0.75 fsec
Coefficient of Runoff (CPRE) = 0.38
**NOTE: Minimum Tc allowed = 10 min.
2 YEAR FREQUENCY. RA TE OF DISCHARGE (Q)
Coefficient (e) =
Coefficient (b) =
Coefficient (d) =
0.806
65
8
5 YEAR FREQUENCY. RATE OF DISCHARGE (Q)
Coefficient (e) = 0.785
Coefficient (b) = 76
Coefficient (d) = 8.5
10 YEAR FREQUENCY. RATE OF DISCHARGE (Q)
Coefficient (e) =
Coefficient (b) =
Coefficient (d) =
0.763
80
8.5
25 YEAR FREQUENCY. RA TE OF DISCHARGE (Q)
Coefficient (e) = 0.754
Coefficient (b) =
Coefficient (d) =
89
8.5
50 YEAR FREQUENCY. RA TE OF DISCHARGE (Q)
Coefficient (e) = 0.745
Coefficient (b) =
Coefficient (d) =
98
8.5
100 YEAR FREQUENCY. RA TE OF DISCHARGE (Q)
Coefficient (e) = 0.73
Coefficient (b) = 96
Coefficient (d) = 8
000761-3357 Drainage Calculations.xis
RESULT
TqPRE) = 9.8 min.
Rainfall Intensity (15) = 7.693 in/hr
········.·.·.·.·.·•·.·.·.·.·.·.·.··· ·········-·.·.·.·.·.·.·.·.·.·.·.·.·.·. ·············.·.·.·.·.·.·,·.·.·,····· @~!.! : nm :rn 1;11tif.~ n
Rainfall Intensity (110) = 8.635 i%r
@jM\K : n =:::::::::::::: ·1~i1~~t!':::::m
Rainfall Intensity (125) = 9.861 i%r
l @~~a ] . i :: m : : : ZiilllV.$f
Rainfall Intensity (150) = 11 .148 in/hr
g~ij !l .··· : :J::::J: :: ' : l~ill:::Rt!::: i>
Rainfall Intensity (1100) 11 .639 i%r
:1~00.:a :: :::rr r: : r=:: t4l.9.'=if.$ n
POST-DEVELOPMENT
GENERAL INFORMATION
Description: Drainage area of site after development
Drainage Area (A1) = 1.400 acres (impervious area)
Drainage Area (A2) = 0.620 acres (landscaped area)
TIME OF CONCENTRATION CTcl
GIVEN
Maximum Travel Distance (D1) =
Velocity of Runoff (V1) =
Coefficient of Runoff (C1) =
Maximum Travel Distance (D2) =
Velocity of Runoff (V2) =
Coefficient of Runoff (C2) =
440 ft
ft 2.75 lsec
0.90
440 ft
1.00 ft/sec
0.45
**NOTE: Minimum Tc allowed = 10 min.
2 YEAR FREQUENCY. RATE OF DISCHARGE (Q)
Coefficient (e) =
Coefficient (b) =
Coefficient (d) =
0.806
65
8
5 YEAR FREQUENCY. RATE OF DISCHARGE (Q)
Coefficient (e) =
Coefficient (b) =
Coefficient (d) =
0.785
76
8.5
10 YEAR FREQUENCY. RATE OF DISCHARGE (Q)
Coefficient (e) =
Coefficient (b) =
Coefficient (d) =
0.763
80
8.5
RESULT
Tc1 =
T C(POST) =
Rainfall Intensity (12) =
Q AREA 1 =
2.7 min.
7.3 min.
10.0 min.
in/ 6.327 hr
8.038 cfs
QAREA 2 = 1 . 780 cfs
liffi :::::: ::]] J:t: ::: ]i~11:~l::£§::
Rainfall Intensity (15) =
Q AREA 1 =
in/ 7.693 hr
9.774 cfs
Q AREA 2 = 2.164 cfs ·ma .·: ::i it 11 ~11 ,m i
Rainfall Intensity (1 10) = 8.635 in/hr
Q AREA 1= 10.970cfs
Q AREA 2 = 2.429 cfs
,gj~.$ i::,: :::,::::i ,, i,, ... ii ,,,:i-::::::::: · 11*1!!i,I!: .. ::.:.::
25 YEAR FREQUENCY. RATE OF DISCHARGE (Q) Rainfall Intensity (125) = 9.861 in/hr
Coefficient (e) =
Coefficient (b) =
Coefficient (d) =
0.754
89
8.5
50 YEAR FREQUENCY. RA TE OF DISCHARGE (Q)
Coefficient (e) =
Coefficient (b) =
Coefficient (d) =
0.745
98
8.5
100 YEAR FREQUENCY. RATE OF DISCHARGE (Q)
Coefficient (e) =
Coefficient (b) =
Coefficient (d) =
000761-3357 Drainage Calculations.xis
0.73
96
8
QAREA 1 = 12.529 cfs
Q AREA2 = 2.774 cfs :·ii':e:.:.]r :::::: :_::_:_::_:::::::,:_:::11~~'~ ~::-<
Rainfall Intensity (150) =
Q AREA 1 =
11.148 in/hr
14.163 cfs
QAREA 2 = 3.136 cfs
ma:]:::· :i::::i:i 1 :: :: ::=:::1z~gnH~r'::::
Rainfall Intensity (1100) 11 .639 in/hr
QAREA 1 = 14.788 cfs
QAREA 2 = 3.27 4 cfs
:1m~1 ::::: ::::: ::11~1@:,f:i
HYDROGRAPHS Chart 4
2-YEAR HYDROGRAPH
4----
2--
0
0 10
I EJ Post-Development 8 Pre-Development I
HYDROGRAPHS Chart 4
= 4,429 ft3
TIME
(min)
20 30
HYDROGRAPHS Chart 5
5-YEAR HYDROGRAPH
0 10 20
8 Post-Development Iii Pre-Development TIME
(min)
HYDROGRAPHS Chart 5
30
HYDROGRAPHS Chart 6
10-YEAR HYDROGRAPH
0 10 20
l!I Post-Development El Pre-Development TIME
(min)
HYDROGRAPHS Chart 6
30
HYDROGRAPHS Chart 7
25-YEAR HYDROGRAPH
10-------
8-----
s----
4---
2
0
0 10 20
ID Post-Development 8 Pre-Development TIME
(min)
HYDROGRAPHS Chart 7
30
HYDROGRAPHS Chart 8
50-YEAR HYDROGRAPH
Volume Conveyed
12-------
a-----
6----
4 --
2
0
0 10
E Post-Development El Pre-Development
HYDROGRAPHS Chart 8
TIME
(min)
20 30
HYDROGRAPHS Chart 9
100-YEAR HYDROGRAPH
Volume Conveyed 8, 148 ft3
10----
5
0
0 10
[J Pre-Development mJ Post-Development
HYDROGRAPHS Chart 9
TIME
(min)
20 30
Project Description
Project File
Worksheet
Flow Element
Method
Solve For
Input Data
Mannings Coefficient
Channel Slope
Left Side Slope
Right Side Slope
Discharge
Results
Depth
Flow Area
Wetted Perimeter
Top Width
Critical Depth
Critical Slope
Velocity
Velocity Head
Specific Energy
Froude Number
Flow is supercritical.
Notes:
APPENDIX A
Worksheet for Triangular Channel
i :\projects\ 700\3357 -p&m bank\drainage report\335 7t1 ra. fm2
(POST) Pilot Channel (1 /3 -5 YR)
Triangular Channel
Manning's Formula
Channel Depth
0.013
2.50 %
4 H :V
4 H :V
3.979 cfs
0.40 ft
0.65 ft2
3.33 ft
3.23 ft
0.57 ft
0.003891 ft/ft
6.10 ft/s
0.58 ft
0.98 ft
2.39
Post-Development Conditions
05/04101
11:29:58 AM
Municipal Development Group
Haestad Methods, Inc. 37 Brookside Road W aterbury, CT 06708 (203) 755-1666
FlowMaster v5.07
Page 1 of 1
Project Description
Project File
Worksheet
Flow Element
Method
Solve For
Input Data
Mannings Coefficient
Channel Slope
Left Side Slope
Right Side Slope
Discharge
Results
Depth
Flow Area
Wetted Perimeter
Top Width
Critical Depth
Critical Slope
Velocity
Velocity Head
Specific Energy
Froude Number
Flow is supercritical.
Notes:
APPENDIX A
Worksheet for Triangular Channel
i:\projects\700\3357-p&m bank\drainage report\3357t1 ra .fm2
(PRE) Pilot Channel (1 /3 -5 YR)
Triangular Channel
Manning's Formula
Channel Depth
0.013
10.00 %
4 H :V
4 H :V
1.980 cfs
0.24 ft
0.23 ft2
1.98 ft
1.92 ft
0.43 ft
0.004270 ft/ft
8.61 ft/s
1.15 ft
1.39 ft
4.39
Pre-Development Conditions
05/04101
11 :43:16 AM
Municipal Development Group
Haestad Methods, Inc. 37 Brookside Road W aterbury, CT 06708 (203) 755-1 666
FlowMaster v5.07
Page 1 of 1
SHARP CRESTED IRREGULAR WEIR TABLE I -WEffi PARAMETERS STAGE ONE STAGE TWO ~::;ht ···1·············•••••:··········~~~~··: ~::;ht I ii .11~~1•: Slopes 1: tt: Q(Ql!ftlft Slopes 1: : :@ !~Mf?,Qft/ft TABLE II-WEm FLOW CALCULATIONS Rainfall Event (yr) 2 5 10 25 50 100 Head h (ft) 0.00 0.10 0.20 0.30 0.40 0.50 0.60 Corrected Average Length L = LAvG-0.lh L (ft) 1.75 1.79 1.82 1.86 1.89 1.93 1.96 1.97 2.02 2.06 2.10 2.15 2.16 Calculated Allowable Weir Discharge Discharge Coefficent Rate Rate Q = CwLh312 C)I) Q Qw.ow (cfs) (cfs) 3.32 0.00 3.32 0.19 3.32 0.54 3.30 1.01 3.28 1.57 3.27 2.23 3.26 2.97 3.26 3.29 3.26 4.54 3.26 5.54 3.25 6.83 3.25 8.38 3.25 9.01 Weir Average Contraction Length Correction LAVG O.lh (ft) 1.75 0.00 1.80 0.01 1.84 0.02 1.89 0.03 1.93 0.04 1.98 0.05 2.02 2.04 2.10 2.15 2.20 2.26 2.28 0.06 0.06 0.08 0.09 0.10 0.11 0.12 Notes: (1) Weir coefficents are from Table 10.3 (pg 325) of McGraw-Hill series in Water Resources and Environmental Engineering, 4th edition. I ]{{ : I Shading indicates given values. (2) 000761-3357 Sharp Crested Irregular-Shaped Weir.xis
000761-3357 Drainage Report.doc
APPENDIXB
MAPPING
DESCRIPTION
APPENDIXB
TABLE OF CONTENTS
PAGE NO.
Exhibit # 1 -Carter's Creek Drainage Basin ................................................................ B-1
Exhibit #2 -Sub-Drainage Basin ................................................................................. B-2
Exhibit #3 -FIRM Map .............................................................................................. B-3
000761-3357 Drainage Report.doc