HomeMy WebLinkAboutDrainage ReportDrainage Report
for
Universal Computer Services
Phase 2 -Parking Lot Expansion
The Business Center at College Station
College Station, Texas
October 2001
Developer:
Universal Computer Services
200 Quality Circle
College Station, Texas 77845
Prepared By:
TEXCON General Contractors
1707 Graham Rd.
College Station, TX 77845
979/690-7711 FILE
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COLLEGE STA
ENGINEERING
CERTIFICATION
I, Joseph P. Schultz, Licensed Professional Engineer No. 65889, State of Texas, certify that
this report for the drainage design for the Universal Computer Services, Phase 2 -Parking
Lot Expansion, was prepared by me in accordance with the provisions of the City of
College Station Drainage Policy and Design Standards for the owners hereof and that the
storm water runoff will be reduced to pre-development runoff values by routing the runoff
through the existing detention facility.
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INTRODUCTION
DRAINAGE REPORT
UNIVERSAL COMPUTER SERVICES
The purpose of this repoii is to provide the hydrological effects of the construction of the
Universal Computer Services, Phase 2 -Parking Lot Expansion project. The proj ect
consists of the 200-space expansion of the existing parking Jot at the existing facility.
GENERAL LOCATION AND DESCRIPTION
The project is located on a 31.85 acre tract located east of Lakeway Drive. The property is
designated as Lots 1 & 2, Block 2 of the Business Center at College Station, Phase I. The
·site of the proposed parking lot expansion is wooded with the vegetation primarily
consisting of oak trees and yaupons. The existing ground elevations range from elevation
272 to elevation 260.
FLOOD HAZARD INFORMATION:
The project site is located in the Lick Creek Drainage Basin. The site is located in a Zone X
Area according to the Flood Insurance Rate Map prepared by the Federal Emergency
Management Agency for Brazos County, Texas and incorporated areas dated July 2, 1992,
panel number 48041 C0205C. A Zone X Area is in an area determined to be outside of the
500-yr floodplain.
DEVELOPMENT DRAINAGE PATTERNS:
The storm water runoff from the site currently drains into the existing detention pond or to
Lakeway Drive or Quality Circle. The design of the storm sewer system and detention
pond was performed by Kling Engineering & Surveying, 4103 Texas Avenue, Suite 212,
Bryan, Texas, 77802. Their design reports were reviewed to evaluate the effect, if any, this
proposed development would have on the existing facilities. Their reports are:
Drainage Report -Dated April 13, 1998
Addendum to Drainage Report Dated April 13, 1998 -Dated June 23, 1998.
The review of the reports indicates that the proposed future development of the Universal
Computer Services facility was considered in the design of the detention pond. Ari analysis
of the Phase I development and Phase II or future development were each considered in the
design of the detention pond.
The proposed parking lot expansion is located within Drainage Area 4C, shown on the
drainage area map in Appendix 2 of the Addendum to the Drainage Report. The Phase II
hydro logic calculations show Drainage Area 4C to be 1.851 acres of Landscaped Area and
5.553 acres of Impervious Area with no undeveloped area noted. Approximately 3.414
acres will be landscaped, 2.290 acres will be impervious, and 1.700 acres will remain
undeveloped after the parking lot expansion construction.
A field survey of the detention pond indicates that the detention pond was constructed
slightly larger than what was shown in the design plans. In order to construct the
2
southwestern comer of the proposed parking lot, it is proposed to fill some of the area of the
existing detention pond and construct it to the original design contours. This is shown on
the grading plan for the parking lot.
DRAINAGE DESIGN CRITERIA
The design parameters fo r the storm sewer are as follows:
•.· The Rational Method is utilized to determine peak storm water runoff rates for the
onsite storm sewer design.
• Design Storm Frequency-Storm Sewer system-10 yr. and 100 yr. storm event.
· • Runoff Coefficients
-Undeveloped Area
-Impervious Area -Pavement and Building Roofs
-Landscaped Area
c = 0.20
c = 0.90
c = 0.50
• Rainfall Intensity values are from the Intensity-Duration-Frequency Curves for the City
of College Station (Figure ill-I -Drainage Policy and Design Standards) for a Time of
Concentration, Tc, of 10 minutes.
Storm Event
10 yr.
Rainfall Intensity (in/hr)
8.635
100 yr. 11 .639
• Time of Concentration -The calculated time of concentration for the onsite storm
sewer system drainage area is less than 10 minutes for the post-development condition.
A minimum time of concentration of 10 minutes was used for the post-development
runoff calculations for the storm sewer system.
STORM WATER RUNOFF DETERMINATION
The drainage area for the proposed parking lot is shown on the drainage area map. The
post-development peak runoff for the proposed parking lot drainage area was
determined in accordance with the criteria presented in the previous section for the 10
and 100 year storm events. The results for the post-development areas are presented
below.
Pavement -Impervious
Landscaped Area
Undisturbed Area
Total Drainage Area
For C = 0.90, A = 1.86 acres
For C = 0.50, A = 0.43 acres
Total Area = 2.29 acres
11 0 = 8.635 in/hr
11 00 = 11.639 in/hr
81 ,000 sf
18,544 sf
0 sf
99,544 sf
c = 0.90
c = 0.50 c = 0.20
Composite C = 0.82
Q10 = 2.29(0.82)(8.635) = 16.2 1 cfs
Q100 = 2.29(0.82)(11.639) = 21.86 cfs
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1111111111 1 1 n II
DRAINAGE AREA MAP
Universal Computer Services
Parking Lot Expansion
College Stotion Business Center
College Station, Texas
TEX CON
General Contractors
1707 Orahom lood l:::r.:O~·, Toot nus
HEAOWAU.
CONCRETE FUME
I
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I I I I ______ _...,..
I
I
I
I
I
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EXISTING
DETENTION PONO
---------
--
11 I 111
---
~~~~~
30 0 E
SCALE IN FEET
STORM SEWER DESIGN
The proposed parking lot will be constructed adjacent to the existing parking lot. The
storm water runoff in the existing parking lot is captured by grate inlets and enters the
stonn sewer system, which discharges into the existing channel. This channel is a part
of the detention pond. The proposed parking lot will have its own storm sewer system.
The runoff will flow to the southeast end of the parking lot near the detention pond
where it will be captured by a grate inlet. A 27" RCP will take the runoff to the
detention pond and discharge from a concrete headwall into a proposed concrete flume,
which will connect to the existing flume in the detention pond.
The storm sewer inlet is designed to collect the runoff for the 10 year storm event for
each drainage area without the depth of water in the parking lot exceeding six inches.
Table 1 presents a summary of the storm sewer inlet design.
The storm sewer piping for this project has been selected to be RCP meeting the
requirements of ASTM C-76, Class ill, pipe. The grate inlet box and headwall will be
cast-in-place or pre-cast concrete. The 27" RCP will pass the 10-year storm without
any headwater and with 3.1' of headwater for the 100-year storm. The tail water for the
storm sewer design was taken from the detention pond design water surface. The
design calculations for the pipes are in Appendix A.
The concrete flume is designed to contain the 100-year storm runoff. The design
calculations for the flume are also in Appendix A.
TABLE 1 -Storm Sewer Inlet Calculations
-----------:::-->'-.!1.l!o--=-=1'-"6=.2::....:1,_c=f:=s _____ ~0100 = 27 .33 cfs
Grate Inlet Open Area Reg'd Cft2) 5.95 6.21
Area Provided Cft:2) 6.53 6.53
Type of Inlet: 2 -Grate Inlets 32"x32", Model No. V-5732
Notes:
1. Grate inlet capacity determined from Figure V-2, City of College Station
Drainage and Design Standards and reduced by 25% for clogging.
2. Maximum inlet depth= 6" for Q10
3. Maximum inlet depth= 10" for Q100
CONCLUSIONS
The construction of this project will increase the storm water runoff from this site. No
flood damage to downstream landowners is expected as a result of this development
since the runoff will enter the existing detention pond, which was previously designed
to include this development.
4
APPENDIX A
Storm Sewer Pipe Design Calculations
Concrete Flume Design Calculations
5
Storm Sewer Pi pe -10 yr St orm
Culvert Ca l culator
Entered Data :
Shape .......................... .
Number of Barrels .............. .
Solving for .................... .
Chart Number ................... .
Scal e Nu mber ................... .
Chart Descript ion
LED RING ENTRANC E
Scale De c sription
WALL
Flowr ate ....................... .
.Manning's n .................... .
Roadway Elevation .............. .
Inlet Elevation ................ .
Outlet Elevation ............... .
Diameter ....................... .
Length ......................... .
Entrance Loss .................. .
Tailwater ...................... .
Computed Results:
He a dwater ...................... .
Slope .......................... .
Velocity ....................... .
Circular
1
Headwat er
1
1
CONCRETE PI PE COL VERT ; NO BEVE
SQUARE EDGE ENT RAN CE WI TH HEAD
1 6 .2 100 cfs
0 .0140
2 64.5000 ft
260.5000 ft
2 60.02 00 ft
27.0000 in
48.0000 ft
0.0000
2 .2 000 ft
262 .6554 ft From Inlet
0.0100 ft/ft
7.4525 fps
Storm Sewe r Pipe -100 yr St orm
Culvert Cal c ula t o r
Ente r ed Data :
Sh ape .......................... .
Number of Barrels .............. .
So l ving for .................... .
Ch a r t Numbe r ................... .
Sc ale Numbe r ................... .
Chart Description .............. .
LED RING EN TRAN CE
Scale Decsription
WALL
Flowrate ....................... .
.Manning' s n .................... .
Roadway Elevation .............. .
Inlet Elevation ................ .
Outle t Elevation ............... .
Diameter ....................... .
Length ......................... .
Entrance Loss .................. .
Tailwater ...................... .
Computed Results :
Headwater ...................... .
Slope .......................... .
Velocity ....................... .
Ci rcular
1
He adwater
1
1
CONCRETE PIPE CULVE RT ; NO BEVE
SQUARE EDGE ENTRANCE WIT H HEAD
21. 8600 c fs
0.0140
264 .5000 ft
260 .5000 ft
260 .0200 ft
27 .0000 in
48.0000 ft
0.0000
3.3000 ft
263 .5857 ft From Outlet
0.0100 ft/ft
5.4979 fps
Concrete Flume -100 yr storm
Channel Calculator
Given Input Data :
Shape .......................... .
Solving for .................... .
Flowrate ....................... .
Slope .......................... .
Manning 's n .................... .
Height ......................... .
Bottom width ................... .
Left slope ..................... .
.Right slope .................... .
Computed Results :
Depth .......................... .
Velocity ....................... .
Flow area ...................... .
Flow perimeter ................. .
Hydraulic radius ............... .
Top width ...................... .
Area ........................... .
Perimeter ...................... .
Percent full ................... .
Critical Information
Trapezoidal
Depth of Flow
21. 8600 cfs
0.0200 ft /ft
0 .0120
16.0000 in
24 .0000 in
1. 0000 ft /ft
1. 0000 ft/ft
8 .7962 in
10.9117 fps
2 .0033 ft2
48 .8794 in
5.9019 in
41.5924 in
4 .4444 ft2
69 .2548 in
54 .9763 %
Critical depth .................. 14.9868 in
Critical slope .................. 0 .0029 ft /ft
Critical velocity ............... 5 .3875 fps
Critical area ................... 4 .0576 ft2
Critical perimeter .............. 66 .3892 in
Critical hydraulic radius ....... 8.80 1 0 in
Critical top width .............. 53 .9737 in
Specific energy . . . . . . . . . . . . . . . . . 2 .5834 ft
Minimum e nergy . . . . . . . . . . . . . . . . . . 1 .8734 ft
Froude number ................... 2 .5 303
Flow condition . . . . . . . . . . . . . . . . . . Supercritical