The role of green stormwater infrastructure in flood mitigation (Detroit, MI USA) - case study

Increased precipitation, ageing infrastructure, and rising surface water levels have exacerbated stormwater issues in the city of Detroit, causing combined sewer overflows and basement flooding. Green stormwater infrastructure (GSI) is now a requirement of the city as part of its stormwater discharge permit to decrease stormwater system overflows. While GSI has been shown to improve water quality in combined sewer overflows, there has been widely-varying conclusions in flood mitigation potential. This study applied a calibrated EPA Stormwater Management Model (EPA SWMM) to investigate the potential flood mitigation benefits of GSI at a neighborhood scale in the city of Detroit. Results suggest the greatest flood mitigation occurs when locating larger scale GSI (i.e. bioretention basin, bioswale, green roof) in areas that are towards the upstream end of the storm sewer system. However, smaller-scale GSI systems (i.e. rain gardens) were also shown to be effective in flood mitigation in limited cases.