Floodplain Restoration for Stormwater Management: Reducing Runoff from Development and Climate Change
Drew Altland, PE
Straughan Environmental, Inc.
Philadelphia, PA
Impacts from elevated runoff conditions and flooding are ubiquitous in the Eastern US due to a long history of land use modification, floodplain filling, and floodplain encroachment. These conditions have been exacerbated by increased intense rainfall patterns and sea level rise, which are symptoms of climate change. Land use modifications began during the colonial era by widespread forest clearing and conversion to agricultural lands. Nearly all virgin timber within the Eastern US was cleared by 1900. During this era, massive amounts of hillside sediment eroded from the landscape and collected in the floodplains. These floodplain deposits, known as legacy sediment, significantly reduce floodplain storage and choke flood flow capacity. Focused urbanization beginning in the mid-1900s increased impervious cover and floodplain encroachment, which typically boosted runoff and intensified storm event discharges while simultaneously reducing flood flow conveyance.
This presentation will demonstrate how floodplain restoration can be used as a stormwater management (SWM) best management practice (BMP) to gain water quantity control benefits to reduce peak discharges, runoff volume, and downstream flooding by reestablishing floodplain storage. The presentation will cover past impacts that make this BMP conducive for water quantity crediting, best-suited restoration approaches to achieve reductions, and floodplain settings that help elevate SWM benefits. Case studies will be presented to demonstrate the water quantity benefits and computation methods used to quantify the discharge and volume reductions.
The Floodplain Restoration BMP has been in practice since 2006 when the Pennsylvania Department of Environmental Protection (DEP) included this BMP in the State’s Stormwater BMP Manual. In 2023, DEP refined and advanced the Floodplain Restoration BMP in the new/draft Pennsylvania Post-Construction Stormwater Management Manual. It is recommended that other jurisdictions adopt this or similar BMPs to reclaim our floodplain areas and daylighting buried streams where feasible with a focus on alleviating downstream flooding. A corresponding benefit of the Floodplain Restoration BMP includes the ability to gain water quality sediment and nutrient reduction credits using established expert panel protocols that are tied to restoring ecological functions. Therefore, this BMP supports both water quantity and quality control SWM requirements.
About Drew Altland, PE
Coming Soon