The Effectiveness of Centralized versus Decentralized Green Infrastructure in Improving Water Quality and Reducing Flooding at the Catchment Scale

Abstract

Green infrastructure (GI), such as green roofs, rain gardens, and porous pavement, is a stormwater management strategy designed to capture rain where it falls and allow it to soak into the ground rather than running off into a stream channel, thus reducing flooding and improving water quality. While there has been a lot of research into the performance of individual GI projects, much less is known about its performance at the catchment scale. This study uses a US EPA SWMM model to examine the effectiveness of GI in improving water quality and reducing flooding at the catchment scale. Results show that in the study catchment, a large centralized wetland was the most effective at reducing and slowing peak discharge. Infiltration based decentralized GI best reduced flood volumes. In addition to changes in effective impervious area, flood volumes were also reduced due to differences in drainage network structure and modifications to the pervious portions of the catchment. Reductions in flood volumes resulted in lower pollutant loads, except for pollutants that are particularly efficiently removed by wetlands. Routing runoff through a large, centralized wetland removed more nitrate load than letting rain infiltrate where it falls.