Influence of Drawdown Period on Overflow Volume and Pollutant Treatment for Detention-Based Stormwater Control Measures in Raleigh, North Carolina

Abstract

AbstractThe drawdown rate of detention-based stormwater control measures (SCMs) influences both the treatment capability of the device and the volume of runoff that becomes untreated overflow. Currently, hydrologic design goals set by the North Carolina Department of Environmental and Natural Resources and other mid-Atlantic U.S. state agencies (e.g., those in Maryland, Virginia, and Pennsylvania) require stormwater practices to treat, e.g., 90% of stormwater runoff (or similar). This equates to a 10% overflow volume, defined as the percentage of inflow volume that bypasses the SCM and therefore receives minimal treatment. For detention-based SCMs, this design goal is met by sizing the outlet to release runoff generated from the water quality event (in North Carolina, either 25 or 38 mm) over a required minimum period of 2 days. Previous studies have not shown whether rainfall patterns in North Carolina and other east coast United States states justify a 2-day drawdown rate of the water quality event to l...