Modeling Techniques of Best Management Practices: Rain Barrels and Rain Gardens Using EPA SWMM-5

Abstract

It is well established that the excess storm-water runoff volume from impervious areas can lead to impairments and water pollution originating from the sewer system overflow and combined sewer systems overflow. This redirection of the runoff into wastewater treatment plants and stream channels can also deprive shallow groundwater tables with recharge, as an impervious surface prevents water from infiltrating to aquifers. The runoff from impervious areas and, in particular, directly connected impervious areas, has been proven to cause the majority of the problem. Controlling the runoff at its source and disconnecting the impervious area from the sewer system is a way to resolve and reduce the impact of excess runoff. This is achieved by implementing specialized detention technologies for runoff reduction. This paper builds on new modeling techniques of two best management practices, rain gardens and rain barrels, implemented in the EPA storm-water management model Version 5 (SWMM-5). The behaviors of a continuously draining rain barrel and an overflowing rain barrel were studied under steady state and unsteady state conditions using C++ and MATLAB programs. The models obtained were compared to a rain barrel conceived within the EPA SWMM-5 subcatchment architecture. Next, a model input was derived to best describe the behavior of a treatment train for water quantity composed of a rain garden, the overflowing rain barrel, and/or the continuously draining rain barrel. A simulated rainfall event in EPA SWMM-5 assesses the results of each subcatchment’s model input and estimates the potential percentage of runoff reduction and the potential reduction in the peak flow and timing of outflow.