HomeMy WebLinkAboutDrainage LetterDecember 10, 2008
Ms. Erika Bridges
City of College Station
1101 Texas Avenue
College Station, Texas 77842
Re: Drainage Letter
Anytime Fitness at Southwest Crossing at Bee Creek
College Station, Texas
Gessner Engineering Job No.: 08-0491
Dear Ms. Bridges:
Gessner Engineering conducted a Drainage Study to determine the affect of adding
twenty-eight (28) parking spaces to the existing development at Southwest Crossing.
The parking is required in order for Anytime Fitness to move into the lease space
available. The total added Phase I area with this parking addition is 0.24 acres (ac).
The amount of this area that is impervious (paving) is 0.21 ac.
Based on the requirements within the Bryan College Station Unified
Code 2008 , Gessner Engineering utilized the Rational Method to
conduct a comparison study on the existing and proposed site . The
Rational Formula runoff coefficient of 0.9 was used for the added parking
impervious area.
The time of concentration (Tc) for the site was calculated to be less than
ten (10) minutes for this parking addition, therefore the minimum time of
concentration (Tc) of ten (10) minutes was used per Unified Stormwater
Design Guidelines.
The Rainfall Intensity and Discharge was calculated for the Ten (10),
twenty-five (25), fifty (50) and one-hundred (100) year storm events
according to the Unified Stormwater Design Guidelines and the results
can be seen in Table 1.
Storm Event Intensity (in/hr) Discharge (cfs , Q=c*l*A
10 8.63 1.63 r------~~~~--+~~~~~~--t-~~~~-
25 9.86 1.86
r------~~~~--t~~~~~~---+-~~~~-
50 11.15 2.11 -------4
100 11.64 2.20 '----~~~~-----'~~~~~~-----'-~~~~-
Table 1
It is in the opinion of Gessner Engineering that the additional 2.20 cubic
feet per second (cfs) of runoff due to this development will not adversely
affect the existing development and detention should not be required or
necessary.
G
Gessner
Engineering
1712 Southwest Pkwy
Suite I 05
College Station, Texas 77840
P.O. Box 10763, 77842-0763
979.680 8840
FAX 979.680.8841
2204 S. Chappell Hill St.
Brenham, Texas 77833
979.836.6855
FAX 979.836.6847
In addition, when the original Drainage Study for the Bee Creek Triutary was completed
with the initial Phase I design of Southwest Crossing at Bee Creek, the entire
development, including future development was taken into consideration . Furthermore,
it is Gessner Engineering's professional opinion that these proposed improvements are
in accordance with the previously approved drainage report for this development and
will cause no adverse affect to other developments upstream or downstream.
We appreciate the opportunity to work with you on this phase of the project. We trust
that this report is responsive to the requirements. Please contact us if you have any
questions or if we can be of further assistance.
Sincerely,
GESSNER ENGINEERING
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Melissa P. Thomas, P.E.
Gessner Engineering