Stormwater Quality Capture Volume for Mitigating Urban Runoff Impacts

Abstract

Porous basins have been recommended for stormwater onsite infiltration and filtering purposes. The effectiveness of a porous basin is often evaluated by its long-term storm runoff capture rate. The key factors for estimating the runoff capture rate include local average rainfall event-depth, tributary watershed’s imperviousness, basin’s storage volume, and drain time. In this study, two sets of empirical formulas are developed from 34 long-term hourly rainfall records observed in the continental US. These empirical formulas are employed to produce the synthetic runoff volume and event capture curves, according to the basin’s drain time. All synthetic runoff capture curves exhibit similar characteristics to the exponential nonexceedance probability distribution. It is concluded that the basin’s storage volume increases as the drain time increases, and the exponential curve serves as the limiting case when the basin has a prolonged drain time due to debris clogging. It is recommended that the two sets of new empirical formulas be used to size the water quality basin if the basin’s operation is warranted; otherwise, the simplified exponential distribution should be employed as a conservative approach.