Stormwater Pond Rehabilitation
Shield was contracted to evaluate cost-effective design options to repair and rehabilitate ten (10) existing stormwater ponds located throughout a large tract of private properties. The ponds were estimated to be over 40-years old and showed signs of deteriorating concrete side walls, leaking outfall risers, failing inlet and outlet pipes, and eroding embankments and berms. Shield evaluated the existing outfall risers and based on the existing drainage areas that fed each pond calculated whether or not the 100-Year, SCS 24-Hour design storm would overtop the existing embankments. In the few instances that a pond did not contain the entire storm event, Shield was able to make proposed adjustments to the ponds’ characteristics (outfall riser, pond size/volume, outlet pipe, etc.) in order to avoid the overtopping activities. All of the existing risers were allowed to stay in place which helped avoid the need to construct new concrete risers and their new connections to the existing outfall pipes. Shield also designed two separate alternatives to replace the existing concrete side walls: similar replacement of existing conditions with like concrete, including stairs, splash pads, and heavy equipment entry ramp, and replacing the side walls with a less-costly geo-membrane material alternative.
By using various design techniques, Shield was able to keep the overall configuration of almost all ponds intact and make use of their existing outfall risers, thus keeping the grading and overall construction costs lower. By also comparing two different side slope options through a cost / benefit analysis, Shield allowed the client to decide that the geo-membrane lining better suited their allocated budget for the project at hand.