HomeMy WebLinkAboutFinal Drainage StudySeptember 22, 2008
Ms. Erika Bridges
City of College Station
1101 Texas Avenue
College Station, Texas 77842
Re : Civil Engineering -Final Drainage Study
Proposed Zeta Tau Alpha Sorority House
1403 Athens Drive
College Station, Texas
Gessner Engineering Job No.: 08-0071
Dear Ms. Bridges:
Gessner Engineering was requested to conduct a drainage study for the
proposed Zeta Tau Alpha Sorority house located in College Station , Texas.
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 drainage. The design was based on a 100 year
frequency with an intensity of 8.14 inches per hour. A runoff coefficient used for
impervious areas was 0.90 and 0.15 for grass or landscape areas.
Based on final calculations comparing the proposed site to the
existing, the proposed construction will not increase the impervious
area. The proposed construction shall be a two story brick veneer
structure with a footprint of approximately 10,600 square foot. The
proposed site shall provide seventy-nine parking spaces, bicycle
storage, sidewalks, and landscape islands. The existing three story
brick veneer sorority house demolished had only a footprint of
approximately 5,200 square foot. The existing site provided
approximately only seventy-six parking space, sidewalks, and
landscape.
Considering the surrounding existing drainage and the minimal
elevation drop across the site, Gessner Engineering choose to utilize
an alternative parking system, Grasspave2, in multiple locations. This
parking was utilized in areas that were anticipated to be used only
once a week for meetings and other full sorority events. This would
decrease the impervious area on the site and will decrease the existing
outflow. After a complete comparison study and additional grass
paving , the proposed new construction will decrease the outflow
approximately 0.73 cubic feet per second (cfs) as presented in the
table below (Table One). Based on this data, Gessner Engineering
does not anticipate this development will adversely affect the existing
G
Gessner
Engineering
1712 Southwest Pkwy
Suite 105
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
G
infrastructure and onsite detention is not required . For complete calculations
please reference the drainage area maps on page C4.0 and C4.1.
Total Proposed Impervious Area (acres): 0.75 (A2-A6, A19-A34)
Total Existing Impervious Area (acres): 0.84
Total Increased Impervious Area (acres): -0.09 Total Proposed Impervious Area (acres)
-Total Existing Impervious Area (acres)
Total Proposed Outflow, Q (cfs): 5.84 100 year
Total Existing Outflow, Q (cfs): 6.57 100 year
Total Increased Outflow, Q (cfs): -0.73 100 year
Table One: Summary Dramage Calculat1ons (Reference C4.1)
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
Gessner Engineering