HomeMy WebLinkAboutDRAINAGE REPORT D
FOR
WEST POINTE BUILDING CENTER
ROCK PRAIRIE WEST
LOT9
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FEBRUARY 2003
Prepared By: 'k'• • • laAil. ALT N G. GERS
Rogers Engineering Services
1712 Southwest Parkway, Suite 105 .• • 5083 : A'
C ollege Station, Texas 77842 ! j f r
(979) 680 -8840 i�`
CERTIFICATION
I, Alton G. Rogers, Registered Professional Engineer No.50833, State of Texas, certify that
this report for the drainage design for the West Pointe Building Center, Rock Prairie West, Lot 9,
Block 1, was prepared by me in accordance with the provisions of the City of College Station
Drainage Policy and Design Standards for the owners thereof.
.0s.v .tti A �2�y
• ?, litV "* Alto : o - P.E. No. 50833
ALTON G. ROGERS '
/ 4 21% 50833
Drainage Report
Rock Prairie West, Lot 9 Block 1
Table of Contents
West Pointe Building Center
Rock Prairie West, Lot 9, Block 1
Proposed Retail and Warehouse
Introduction• 1
General Location and Description 1
Primary Drainage Basin Description 1_
Drainage Design Criteria 2
Drainage Facility Design 2
Conclusion 3
Exhibits
FEMA Flood Insurance Rate Map Excerpt "A"
Drainage Area Map - Existing Condition "B -1"
Drainage Area Map - Proposed Condition `B -2"
Drainage Area Calculations "c"
Routing Hydrographs "D"
ALT N G. ROGERS
A 08
Drainage Report
Rock Prairie West, Lot 9 Block 1 ii
Storm Drainage Report
West Pointe Building Center
Rock Prairie West, Lot 9, Block 1
Proposed Retail and Warehouse
Introduction:
This storm drainage report is intended to cover the necessary drainage infrastructure for the
proposed development site improvements. The parameters used for design and the existing
conditions of the on -site area are incorporated to show how the final drainage design will accomplish
the desired drainage objectives per the City of College Station Drainage Policy and Design
Standards. (DPDS)
General Location and Description:
The proposed building is located in the southern portion of College Station. The project site
contains one commercial lot located along Old Wellborn Road between Gandy Road and North
Graham Road. The lot is platted as Lot 9, Block 1 Rock Prairie West, and is zoned A -O. The 2.4
acre site is undeveloped cattle pasture and is gently sloping with an average of 1.67% slopes.
The current land cover is considered natural grassland, and the proposed site will contain
both landscaped areas and impervious areas. The proposed site is owned by Mr. Charles Moreau,
of College Station.
Primary Drainage Basin Description:
The current site drains from the northern corner to the southern corner of Lot 9, Block 1 Rock
Prairie West. Storm water that drains to the southeast eventually flows into the South Fork of Lick
Creek. The developed site drains to the south corner of Lot 9.
No portion of the site is within the 500 year flood plain per the Federal Emergency
Management Agency Flood Insurance Rate Map Panel 48041 C0182C.P. for Brazos County, Texas
Drainage Report
Rock Prairie West, Lot 9 Block 1 1
and Incorporated Areas effective July 2, 1992 (see Exhibit "A ").
Drainage Design Criteria:
All drainage design is in accordance with the City DSPS. The design rainstorm is the 10 year
storm event. Flow calculations for all drainage areas are based on the Modified Rational Method.
Storm recurrence intervals used were the 5, 10, 25, 50, 100 year interval storm event.
The storage volume required for the detention facility is based on calculations outlined in the
City DSPS method of subtracting pre- and post - development hydrographs and peak flows computed
using the Rational Method for a ten (10) year design storm event. The site requires 0.21 ac -ft of
storm water storage.
Drainage Facility Design:
The site will be served by a detention facility located along the rear property line. The pond
will consist of an earthen berm with a low flow channel. Exhibit `B" shows the proposed drainage
areas for the pond. The four (4) drainage areas shown were routed simultaneously through the
detention facility. All impervious area created by the buildings and parking lot will be captured and
routed to the detention facility. The study point for the project is the outfall device of the proposed
detention facility. The outlet device for the pond is a 18" RCP outlet pipe with headwalls and energy
dissipaters. The pond basin elevation is set at 321.00'. The top of the berm elevation is 322.00'. The
pond has a storage capacity of 0.22 ac -ft.
Drainage Report
Rock Prairie West, Lot 9 Block 1 2
The following summary table shows the peak flow for the Pre - development events and the peak
flows for the Post - development events.
Study Point - Pond Outfall
Pre - development Pond In Pond Out
Q 3.95 cfs 13.29 cfs 1.93 cfs
Q 4.47 cfs 14.92 cfs 4.03 cfs
Q25 5.13 cfs 17.04 cfs 6.31 cfs
Q50 5.82 cfs 19.26 cfs 8.06 cfs
Qioo 6.07 cfs 20.11 cfs 8.06 cfs
Conclusion:
The Post - development peak discharge does not exceed the Pre - development peak discharge
for the 5, 10, 25, 50, or 100 year event. In all cases, including the 100 year event, storm water is
released into the natural outfall. The drainage design for this site meets the requirements as stated
in the City of College Station Drainage Policy and Design Standards.
Drainage Report
Rock Prairie West, Lot 9 Block 1 3
Exhibit A
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