Effect of Increasing Discharge on Municipal Storm Sewer Systems: Exploring the Connection to Total Maximum Daily Load

Abstract

Climate change and urbanization are resulting in increased runoff for stormwater sewers to handle. This work uses hydraulic modeling and typical US prices to quantify the cost increase due to the larger pumps and pipes that will be needed for various amounts of discharge increase. Analysis was performed on a single sewer pipe and pump but also on a hypothetical system of varying sizes, incorporating cost for pipes pumps, and electricity usage. It was found that gravity-flow systems will cost up to nine times more than the current design amount. Cost increases can be estimated by a linear function with slope ranging from 0.025 to 0.019. The cost can increase by a factor of 0.24 for a 30-pipe system at a slope of 0.0001 and as little as 0.03 for a single pipe system at a slope of 0.0019. For a force main, the cost increase ratio is a function of the discharge ratio to the 0.5 power. For corrugated pipes, the cost ratio varied from 31% to 39% from that of concrete pipe and from 20% to 22% for a PVC pipe, making additional funds necessary. This has implications for total maximum daily load (TMDL) because more stormwater, especially of pollutant concentration greater than the TMDL concentration, will be entering surface water bodies subject to TMDL regulations.