Modeling Rain Garden LID Impacts on Sewer Overflows

Abstract

In September 2010, the U.S. Environmental Protection Agency (USEPA) released a new version (5.0.021) of Storm Water Management Model Version 5 (SWMM5) that offers low impact development (LID) modeling capability for the first time. The same LID modeling capability was soon enabled in the PCSWMM software (Version 2010, from Computational Hydraulic Int.). Five types of LIDs can be modeled in SWMM5 and PCSWMM: bioretention cells (rain gardens), infiltration trenches, porous pavement, cisterns (rain barrels) and vegetative swales. Using these new software releases and real world examples, this chapter presents some LID modeling features of SWMM5 and PCSWMM, input data requirements, modeling procedures, and output results for quantify-ing the LID impacts on sewer overflows. The modeling results presented here can help quantify the LID impacts on sewer overflows and allow sustainable developers to answer questions such as How much rainfall can be captured in a typical design year using a certain type of LID? or How many rain gardens are needed in a sewershed to capture a certain volume of storm water? A predictive model is presented to calculate the optimal number of rain gardens to achieve a target level of sewer overflow control.