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DODSON Our M ission: & ASSOCIA T ES, INC
Hydrologists and Civil Engineers The Best in Water Resources Engineering
May 21, 2008
Mr. David Hamilton, P.E.
Managing Principal
Bury + Partners
1001 West Loop South, Suite 200
Houston, Texas, 77027
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DAI Job No. 1726.3
713-212-0011 (T)
713-212-0010 (F)
Re: No-Rise Hydraulic Analysis for the Place Properties Aerial Sewer Crossing at
Apartment Clubhouse
Dear Mr. Hamilton:
We are pleased to present the results of a hydraulic impact analysis for the proposed structure
to be placed in the channel of an unnamed tributary to White Creek (Exhibits 1 and 2). The
proposed structure is an aerial sanitary sewer crossing which will place several two-foot
diameter piers in the channel. Exhibits 3 provide the details of each proposed structure .
BACKGROUND
The drainage report entitled Floodplain Analysis for a Proposed Student Housing Complex and
Letter of Map Revision Request was submitted to the City of College Station on April 3, 2007 by
Dodson & Associates, Inc. (Dodson) and Mitchell & Morgan , LLP (M&M). The drainage report
presents an existing and proposed conditions hydrologic analysis and an existing conditions
hydraulic analysis for an unnamed tributary to White Creek and three tributaries to the
unnamed tributary to White Creek.
In November 2007, Dodson submitted a no-rise hydraulic analysis memo to the City of College
Station (COCS) for the three channel crossings associated with the apartment development
project. The November 2007 analysis documented that the proposed two culvert crossings and
one aerial sewer crossing did not cause hydraulic impacts in the unnamed tributary to White
Creek or the tributaries to the unnamed tributary to White Creek.
This current hydraulic impact analysis and the November 2007 analysis were completed to
provide a proposed conditions hydraulic analysis for the 2818 Place project and to address the
COCS's requirements for a complete engineering report fully demonstrating that floodway
encroachments shall not result in any increase in water surface elevation.
The hydraulic impact analysis was completed using the HEC-RAS software program version
3.1.3. The analysis compared the water surface elevations for the 1 % annual exceedance
probability (AEP) storm event from existing to proposed conditions. The goal of the analysis
was to show no water surface elevation increases greater than 0.02 feet based on the COCS's
interpretation of what constitutes a "zero-rise." This approach was outlined in an email on
November 9, 2007, and agreed upon in a return email on November 12, 2007.
5629 F.M. 1960 West, Suite 314, Houston, TX 77069-4216
(281) 440-3787 -FAX (281) 440-4742
www.dodson-hydro.com