Evaluating Management Strategies for Urban Stormwater Runoff

Urban stormwater runoff, a leading cause of waterway impairment, has become a focal point of urban stormwater management strategies. As urbanization increases, regulations demanding preservation of pre-development peak flow rates or runoff volumes have been implemented and low impact development (LID) is encouraged as a strategy to achieve this stormwater runoff reduction requirement. While the success of LID has been proven at the site-scale, limited watershed-scale assessment of LID has been conducted. This research explores the potential benefit of watershed-scale LID implementation on two common urban stormwater issues: degraded stream health and combined sewer overflows (CSOs). Assessment results indicate that both stream health and CSO volume reduction are possible for the 1-yr storm event if the percent impervious cover (%IC) can be reduced by 20%. Since a reduction of 20%IC is lofty in a dense urban setting, the practical extent of LID implementation in an existing urban watershed is scrutinized to determine if, based on the constraints of the built environment, LID should be realistically considered by watershed management. In a dense urban environment with typical constraints – requirement to maintain traffic flow, preexisting utility location, public vs. privately owned land, etc. – a 20% IC reduction is unreasonable using one stormwater management best management practice (BMP). To achieve maximum stormwater runoff reduction potential, an integrated, watershed-scale stormwater management approach is encouraged. The results of this study assist watershed managers with decisions about the inclusion of LID while striving to achieve federal stormwater mandates concerning stormwater runoff.