Abstract
A procedure is presented and demonstrated for identifying the minimum interevent time for automatic separation of rainfall events and the subsequent use of the event statistics to determine the water quality volume. The proposed procedure for identifying the minimum interevent time is more robust that the conventional approach that requires interevent times to have an exponential distribution. The procedure is validated in South Florida and at locations in Athens (Georgia), Roanoke (Virginia), and St.Louis (Missouri). Minimum interevent times of 6h, 6h, 12h, and 9h, respectively, were found at the study locations, and it was demonstrated that the interevent times do not generally have an exponential distribution. Conventional determination of the water quality volume does not formally consider the influence of the drain time in sizing the water quality storage basin, and a procedure is presented herein for taking the drain time into account. The procedure is demonstrated at the study locations using multiple rainfall-runoff models. It is shown that a maximum drain time of 24h would not generally be adequate in South Florida, but would be adequate in Athens, Roanoke and St.Louis, however, a maximum drain time of 48h would not generally be adequate at all locations.
•A procedure is presented and demonstrated for identifying the appropriate interevent time for automatically separating rainfall events.•The proposed methodology is validated in four study areas.•It is shown that the conventional assumption of exponentially distributed interevent times is not appropriate at the selected sites.•It is shown that imposing a 24-h drain time on the designs of water-quality basins is not generally adequate.•Appropriate drain times are identified for the study sites.