In 2010, Gwinnett County DWR completed renovations to online detention ponds (2A, 2B, and 2C) within Rivershyre subdivision in Lawrenceville. The design for these modifications was completed by previous engineering firm. The modification to the outlet control structure of pond 2B resulted in an approximately 2 feet increase in flood elevation vs. the platted flood elevation adjacent to the pond. As a result, the County tasked Columbia Engineering to both determine the cause of the increase and determine potential options for solutions to lower the flood elevations to the platted elevations and potentially below the basement finished floor elevations of the adjacent homes.
Columbia analyzed the pond and connected system. A concept report was created that outlined the existing conditions and determined the initial platted elevation was in all likelihood incorrect. In addition, the concept report outlined 11 options for alleviating the flooding of the adjacent homes and lowering the flood elevations. The report recommended a solution of constructing two upstream detention ponds to store water during heavy flow times and release it slowly over 24 hours in order to dissipate the peak flood elevations. This option was chosen by the County to move forward to construction plans. Columbia worked with the County on public outreach including having several meetings with the homeowners and homeowners association at Rivershyre to explain the project, detail the benefits to the homeowners, discuss potential inconveniences during construction, and respond to questions regarding the project. Working together, DWR and Columbia were able to get complete cooperation from the subdivision on the project and allow it to move forward.
Preliminary construction plans for this project have been completed and submitted to DWR. Final plans are expected to be complete by summer of 2016 which will include permitting through Gwinnett County Planning and Development and a 14.5’ retaining wall design. Construction is roughly slated for end of 2016/beginning of 2017.
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