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DRAINAGE DESIGN SUMMARY c�
for -
Washington Chappell Baptist Church p,c
College Station, Texas - June, 2008 TSV
EXECUTIVE SUMMARY
Contact Information:
Project Engineer: Property Owner/Developer: Other Contacts:
Berry Engineering Washington Chappell Baptist Church
Larry Berry, P.E. Lee Thompson, Trustee DeAnna Ordonez
1811 Rose Street 1801 Texas Avenue 1701 Langford
Bryan, Texas 77802 College Station, Texas 77845 College Sta, Tx 77845
Ph: (979) 575-3457 Ph: (979) 693-5145 Ph: (979) 739-1649
General Property Information
The subject property, 0.96 acres, located at 1801 S. Texas Avenue and being situated in the
MORGAN RECTOR LEAGUE, A-46, College Station, Brazos County, Texas, deed recorded in
volume 44 page 556, Brazos County Deed Records. The property is platted as Lot 1, Block 1,
Tinsley Square Subdivision, final plat recorded in vol. 408 page 329. The property is zoned
Wolf Pen Creek Coridor district.
Project Overview
The subject property is currently developed with a church building and parking lot. It is
proposed to redevelop the parking lot to accomidate more parking, facilate two way traffic and
to provide a cross drive acess to the adjacent property wolf pen plaza. Additional landscaping
and revisions to the sidewalk are proposed as well. See Site Plan and Demo Plan. There are
no proposed changes to the plat or zoning. This drainage summary is to accompany the site
plan, case file #07-00500110.
Project Watershed, FEMA Information and the need for Detention Determined
The project is located in Wolf Pen Creek Watershed Basin. See attached watershed area
exhibit. The entire property, 0.96 acres, is located within a 100 year floodplain according to
Flood Insurance Rate Map, Community Panel No. 48041C0144C; Effective Date: July 2, 1992.
A very small corner of the property is located within the floodway. There is no portion of the
floodway to be developed. Detention of stormwater is not warrented because of the location of
the project within the flood plain and the close proximity to the floodway. The increase in run
off 0.22 cfs is not significant.
Existing Hydrologic Characteristics of Subject Property
The existing 0.96 acre land cover is 0.57 acres impervious and 0.39 acres pervious. Run-off
from the property surface drains through the parking lot to a concrete channel located at the
north end of the parking lot. There is no run-off conveyed from the right-of-way. A small
portion, 0.014 acres, of the adjacent property runs onto the to the subject property where
there is a portion of a cross access drive. Currently there is a temporary curb in line with the
permanent curb that is located on a grade break. Once the temporary curb is removed the
drainage from the shopping center will continue to drain towards the inlet drain as the grade
break will remain the same. Of the 0.014 acres that drain towards the subject property 0.009
acres are impervious with 0.005 ac being pervious. There are not any stormsewers or
detention on the subject property. See pre-developed tributary exhibit.
Proposed Hydrologic Characteristics of Subject Property
The proposed 0.96 acre land cover is 0.60 acres impervious and 0.36 acres pervious. Run-off
from the property surface drains through the parking lot to a concrete channel located at the
north end of the parking lot, as in the existing conditions. There is no run-off conveyed from
the right-of-way to the subject property. There is an additional 0.014 acres impervious cover
run-off conveyed from the adjacent property when the temporay curb is removed and the
cross access drive is constructed. There are not any stormsewers or detention proposed. See
prost-developed tributary exhibit.
Coordination with other Agencies
There is no other agencies that coordination and/or permitting has occurred or is planned.
Summary of the Comparison of Pre-Developed to Post-Development Run-off
The predeveloped tributary consists of the project site 0.96 acre of which 0.57 acres is
impervious and 0.39 acres are pervious. An additional 0.014 acres (0.005 pervious, 0.009
impervious) runs off from the adjacent property where the cross acess easement is stubbed
out. Post development site tributary, 0.96 acres, consists of 0.6 acres impervious and 0.36
acres pervious.
The rational formula was used to determine the peak discharge because the area is a small
and the peak discharges will not be used for determining storage requirements. Pre-
development and post development run off coefficients for the pervious and impervious run-
off was taken from Table C-3 Unified drainage design guidelines 2008 and found to be 0.42
and 0.97, respectively. The weighted runoff coefficient was then calculated to be 0.75 in the
predeveloped state and 0.76 post development. A minimum of 10 minutes is used in
calculating the intensities for the range of storm events. Intensities were calculated using the
formulas in Table C-1 B/CS Unified Drainage Design Manual 2008.
Conclusions
The increase in run-off rate for the 100 yr storm event for the project site was found to be
0.19 cfs. The increase for the in run-off rate for the 100 yr storm event due to the cross acess
drive was found to be 0.03 cfs. The total increase (0.19 cfs + 0.03 cfs ) is 0.22 cfs for the total
development at the 100 yr storm event. See calculation exhibits.
"This report/letter for the drainage design of the development named in the outline above was prepared
under my supervision in accordance with provisions of the Bryan/College Station
Unified Drainage Design Guidelines for the owners of the property. All licenses and permits
required by any and all state and federal regulatory agencies for the proposed drainage
improvements have been issued or fall under applicable general permits."
t5� ` •OF rF91,1
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Licensed Professional Engineer L.A,BERRY J
State of Texas PE No. $i 1'A 7 46
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