Changes in runoff due to stormwater management pond regulations

A continuous simulation stormwater management model (with 33 years of historical precipitation) was used to determine how the design criteria from five different stormwater management pond ordinances changed the runoff from a 7.77 ha watershed following a hypothetical development scenario. All five evaluated ordinances required that the postdevelopment runoff rates from the site be less than or equal to the predevelopment runoff rates for each return period (a zero increase criteria). However, none of the five ordinances were effective at limiting the increase in runoff peak rates for the 1- and 2-year return periods for the annual runoff series, the 1-year return period for the annual exceedance (partial) runoff series duration, or more frequent precipitation events. To better control the lower frequency runoff events from stormwater ponds, the 1- and 2-year return periods should always be analyzed for a basin's design. Additionally, there was a radical change in the frequency of small and moderate runoff events occurring from the watershed following the hypothetical development.