Rainfall within the State of Florida is highly variable, not only with respect to annual rainfall depth, but also in the distribution and frequency of individual rain events which occur in different meteorological regions throughout the State. Differences in the distribution of rainfall events have a significant impact on annual runoff coefficients for both developed and natural areas. A residential development constructed in an area dominated by small rain events which generate little runoff will have a lower runoff coefficient than the same development constructed in an area dominated by larger rain events even if the annual rainfalls are similar. This phenomenon also impacts the performance efficiency of dry retention treatment systems which are designed for a specified treatment depth. Due to the variability in the distribution of rainfall events within the State, a single design standard will not be capable of meeting a specified performance criterion for all areas within the State. Therefore, design criteria for dry retention systems need to be variable throughout the State in response to variability in rainfall characteristics to achieve similar levels of treatment.
In addition, design criteria for dry retention systems must also consider the specific combination of DCIA and non-DCIA curve number for each development. These combinations substantially impact the runoff coefficient for a given development which can impact the performance efficiency of the stormwater management system. A development constructed with a DCIA percentage and a high non-DCIA curve number may require twice as much treatment volume to achieve the target pollutant removal criterion as a project designed with a low percentage DCIA and a low non-DCIA curve number.