A Sensitivity Analysis of the Influence of Watershed and Development Characteristics on the Cumulative Impacts of Stormwater Detention Ponds

Stormwater detention ponds are a popular stormwater management practice in many communities and city ordinances often require the uniform use of detention ponds on all new developments. Stormwater detention ponds are an effective method of controlling the peak flow rate immediately downstream from a development, but a number of detention ponds scattered at random locations throughout a watershed may not effectively control peak flows throughout the watershed.

A sensitivity analysis was conducted to determine correlations between watershed and development characteristics and the response of the watershed to the uniform use of detention ponds on all developments. The cumulative impacts of detention ponds were analyzed for sensitivity to two watershed characteristics: watershed shape and watershed slope. Peak flow impacts were also analyzed for sensitivity to four development characteristics: development size, development intensity, development stage, and development sequence. The sensitivity analysis was conducted by modeling the cumulative effects of detention in watersheds with various combinations of these characteristics.

Synthetic watersheds were used for the sensitivity analysis in order to produce general results and conclusions that can help evaluate the potential for adverse peak flow impacts in any watershed, rather than being specific to a particular watershed. The use of synthetic watersheds also provides a controlled environment that allows the effects of specific variables to be pinpointed. The synthetic watersheds for this analysis were developed using network topology. Following the sensitivity analysis using the synthetic watersheds, a “real-world” test watershed was modeled as a means of evaluating the applicability of the findings of the sensitivity analysis to an actual watershed. The Ten Mile Creek watershed in Knox County, Tennessee was used as the test watershed.

Of the six watershed and development characteristics considered in the sensitivity analysis, watershed shape, the percent of the watershed that was developed, and the location of the developed areas within the watershed had the greatest effect on the cumulative impacts of detention ponds in the watershed. These three factors determined the pattern of impacts that occurred within a watershed. Development intensity, development size, and watershed slope contributed to the magnitude of the impacts which were created, but they were not the overriding factors that determined the pattern of impacts.