Extended Detention Stormwater Basins Outlet Structure Flows - Physical Model Study

摘要

Extended Detention Basins (EDB) are utilized throughout storm water systems to extend the emptying time of the more frequently occurring runoff events to facilitate pollutant removal and reduce the peak runoff that would enter a storm water system. Each EDB has an outlet structure, typically installed in the embankment of the basin that contains water quality orifices, a 10-yr orifice, a sloped weir overflow with trashrack, and a 100-yr orifice downstream of the weir and trashrack to limit the amount of water that can leave the basin. Flows from the extended detention basins can be estimated by measuring the water surface upstream of the outlet. Several attempts have been made to accurately determine the flows from the detention basin outlet. Discrepancies between different methods to calculate the flow from the overflow weir lead to a physical model study to determine what method, if any, should be utilized. A complete EDB outlet structure was modeled at a geometric scale of 1:3. The model study collected data at several overflow outlet weir slopes and grate configurations. The data was used to develop a spreadsheet that can generate an outlet rating based on upstream water surface elevation that can accurately measure flow from an EDB outlet structure.