Effects of Design Practice for Flood Control and Best Management Practices on the Flow-Frequency Curve

Abstract

Peak-flow attenuation is widely used in urban storm-water systems. Standard practice typically involves peak shaving of postdevelopment flows to predevelopment peak-flow levels for given return interval storms. In most cases, the flow controls target low-frequency events (storms equal to or larger than the 2-year event), but not smaller, higher-frequency events. More recent emphasis on removal of pollutants in urban runoff has targeted control of high-frequency events (smaller than the 2-year storm). The question of how the time history of discharges from these facilities compares with the predevelopment flow regime has not been addressed. This study examines the effects of the state of practice for urban flow control. Performance is judged on how well the postdevelopment flow frequency curve matches the predevelopment curve. Continuous simulation, using 50 years of hourly rainfall records, was performed on two climatically different locales. Detention ponds with a variety of orifices sized for peak-flow control using traditional and innovative methods were examined singly and in conjunction with extended detention best management practices.