Stormwater Interception and Storage

Stormwater control devices are constructed to intercept or capture a portion of the design storm with a given runoff flow and duration. The portion will change, however, as the characteristics of the runoff vary from storm to storm. A statistical method of analysis is described, based on a probabilistic characterization of rainfall and runoff, which evaluates the long-term performance efficiency of the devices. Stormwater control devices that capture and store runoff include interceptors and retention basins. The long-term average performance of interceptors and storage devices are determined based on the size and operational mode of the devices, and the statistical properties of the runoff. Issues addressed include the effect of previous storms on storage and the emptying rate of the basin, flow variations between and within storms, and the treatment implications of the first flush effect and flow-concentration correlations.