Analysis of detention ponds for storm water quality control

Flow capture efficiency and average detention time are the performance meas ures commonly used in assessing the long-term pollutant removal effectivene ss of storm water detention ponds. A statistical formulation is presented f or estimating these two performance measures for typical detention ponds wh ere outflow is controlled by an orifice or weir type structure. The flow ca pture efficiency is determined with the estimation of the total spill volum e. The total spill volume is calculated as the combination of the event spi ll volume and the carryover spill volume. Thus the carryover effect of cons ecutive runoff events is quantified. A closed-form analytical expression is derived for estimating the average volume-weighted detention time, taking into account the variable inflow and outflow rates and the random spacing b etween runoff events. Analytical determinations of the average detention ti me are confirmed by continuous simulation modeling. Statistical solutions o f flow capture efficiency closely resemble those obtained from continuous s imulation models. The statistical models presented, and the insights gained from their use, can be applied in the design or evaluation of detention po nds for storm water quality control.