Pluvial Flood Risk Estimation Procedure for Small Urban Watersheds

Abstract

Pluvial flooding, when runoff causes flooding before it reaches a body of water, is a type of flooding that often is overlooked in flood risk studies. This study outlines a general procedure that can be used to model urban pluvial flood scenarios, estimate damages, and quantify pluvial flood risk for microwatersheds (watersheds of a few square miles or less). The model development was accomplished using EPA's SWMM in combination with GIS datasets and analyses. Sensitivity analyses were performed on many model inputs including runoff surface slope, imperviousness, infiltration parameters, and pipe roughness. The overall procedure was tested on a 215-acre sewershed in Washington, DC. The results indicate that pluvial flooding can have serious consequences, even in areas that are not close to existing bodies of water and are at relatively high elevations. The 10-, 100-, and 200-yr rainfall events modeled produced damage estimates of approximately $430,000, $904,000, and $1,093,000, respectively.