Using LID Retrofits for Flood Control and to Achieve Receiving Water Quality Standards

Many older communities were developed prior to the existence of regulations and design guidance for managing floodplains and other wet weather flows. This has resulted in untreated stormwater runoff that floods roadways, inhabited structures and floodplains. A common limitation is that urban residential areas were built without the preservation of natural areas or publicly owned open space. These construction practices limit opportunities to implement structural measures to mitigate increased stormwater runoff volumes and elevated pollutant loads. Low Impact Development (LID) small scale, on-site structures provide a method for mitigating stormwater runoff within the confines of the limited open space available. Fairfax County, Virginia, has been working with two residential communities to mitigate flooding concerns at the sub-watershed scale. This paper describes the processes used to select and evaluate flood mitigation alternatives, how the LID opportunities were selected and implemented, and the resultant mitigation of the hydrologic impact of these built areas.