Assessing the Impacts of LID Infiltration Practices in Philadelphia

The Philadelphia Water Department is proposing a unique approach to address their stormwater and combined sewer overflows problems. The approach will rely heavily on unprecedented levels of low impact development or green infrastructure to capture and infiltrate the first inch of rainfall. This program, part of Philadelphia’s Sustainability Initiative, aims to convert over 50% of all impervious cover in the city to manage the first inch of rainfall, relying heavily on infiltration of street and roof runoff. One issue that has not yet been adequately addressed is to assess the impacts of concentrated infiltration on water table elevations, both locally near the infiltration facilities, and on a city-wide scale as infiltration is increased through full implementation of the program. This paper addresses the modeling studies that have been carried out to answer important questions about potential basement flooding and impacts to building foundations as a result of the proposed Green Infrastructure Program.