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Bryan, Texas


Brazos Transit District 


Gessner Engineering, LLC 


Roan Commercial Group, LLC 



Technical Description:

300LF 54” ALT2 CMP

The Brazos Transit District desired to develop an additional administration building on its existing headquarters site in Bryan, Texas. The project called for the development of an 11,000 square foot single-story building and parking on a 1.2-acre portion of a 6.4-acre site. The majority of the existing site contained on-site parking and maintenance of the District’s fleet vehicles, as well as their existing administration building. As a result, the site did not have enough area to allow for surface detention to manage the stormwater requirements of the new building. As such, the design engineer was tasked with identifying an underground detention solution to detain 4,800 cubic feet (cf) of volume.

With any existing site, one of the challenges with adding structures or additions to existing structures, is finding the surface area to meet the additional stormwater detention requirements. In the case of the Brazos transit project, the majority of the surface area for the site needed to be utilized for access to buildings, leaving underground detention as the most viable option for stormwater management. The initial design was made using Contech’s Design Your Own Detention System Tool. Located on the Contech website, this free tool allows engineers to quickly review layout options and produce site-specific drawings for the creation of plans and specifications.

The detention system was made from 300’ of 54” diameter corrugated metal pipe CMP), providing 4,835 cf storage.The outfall system was designed to discharge into the existing storm system located adjacent to the new underground detention. Utilizing CMP allowed 100% of the storage volume to be captured within the pipe.

“This site lacked real estate required for a surface detention pond and required an underground solution for the detention system,” stated Melissa Thomas, Project Manager for Gessner Engineering. “Contech’s online design software is extremely helpful and intuitive, making it easy to get an idea of the footprint required for the system with the given restraints and even providing an Autocad file to insert into the site plan. By using the Contech system, we were able to efficiently provide a solution which met the projects needs in achieving the detention volume required.  We enjoyed working with the Contech team and look forward to future projects.”

Technical Description:

300LF 54” ALT2 CMP

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