HomeMy WebLinkAboutDrainage Letter 4 � 7607 Eastmark Drive, Ste. 252 -A <77840>
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P.O. Box 9253, College Station, TX 77842
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email: civil @ rmengineer.com
August 11, 2010
Josh Norton, P.E.
Assistant City Engineer
City of College Station
Planning & Development Services
1101 Texas Avenue South
College Station, TX 77842
RE: F.S. Kapchinski, Block One — Reminder of Lot 18
1602 Park Place — College Station, TX
Drainage Letter
RME No. 220 -0408
Josh:
The above referenced project is proposed to include the development of approximately 2,650
sq.ft. of new impervious area (residential building and associated parking) within the proposed
Lot 18R4. Drainage from this development will be conveyed overland and into the existing
drainage stormsewer conveyance elements northwest of the site via Park Place. Runoff will then
be conveyed by means of surface and underground drainage to the Wolf Pen Creek.
Development conditions are anticipated to yield increased runoff of approximately 0.35 cfs
during the 100 -year rainfall event (within the new Lot 18R4). Calculations for this runoff rate
are calculated using the Rational Method with the following assumptions.
Rational Method: Q =CIA where,
Q = runoff rate (cfs)
C = change in runoff coefficient (unitless): CE =0.39 & CPR =0.95
I = 100 -year rainfall intensity (in/hr): 11.63 in/hr
A = runoff area (acres): 0.061 acres
Q =0.56x 11.63 x0.061 = 0.40cfs
Per Table #7, recorded in a Drainage Report (dated 9/14/09) for the Boardwalk Court
development, there is approximately 0.98 cfs additional capacity within the detention facility
which is located at the south end of the subdivision. Per Table #10, of the same report, there is
sufficient capacity in the drainage structures under and downstream of Park Place to handle the
proposed increased runoff rates.
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M � 7607 Eastmark Drive, Ste. 252 -A <77840>
P.O. Box 9253, College Station, TX 77842
Off /Fax: (979) 764 -0704
Go►.sclt�ny Err
email: civil @rmengineer.com
Please do not hesitate to call if you have any questions.
Sincerely,
PEE OF TE
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Rabon A. Metcalf, P.E. No. 88583
Texas Firm Registration No. F -4695
rabon @rmengineer.com
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