Comparison of Stormwater Management Strategies with an Urban Watershed Model

Abstract

A detailed hydrologic/hydraulic model for an urbanized 381-acre watershed in Blacksburg, Virginia, is used to evaluate downstream results from simulation of seven stormwater management (SWM) strategies currently practiced within the United States. Each strategy has unique design criteria for specified design storms and is intended to achieve predevelopment peak runoff rates at the site outfall or a baseline peak runoff rate at a watershed point of interest (POI). Model simulations are run that represent each strategy implemented throughout the watershed within areas currently subjected to SWM. Runoff hydrographs at each site outfall and the watershed POI are evaluated. Evaluation of model results at the site outfalls and a downstream watershed POI lead to a number of observations about the performance of the various strategies and their respective design criteria. Results demonstrate that strategies met the predevelopment peak runoff rate targets for design storms specified in their design criteria at the site outfall. Most strategies did not meet the targets outside of the range of design storms specified in design criteria with the exception of the most frequent storm evaluated when an initial runoff capture and drawdown is required. None of the strategies are found to achieve the baseline peak runoff rates at the watershed POI for a full range of design storms, with almost all strategies failing to meet the baseline target for the more frequent, 1- and 2-year storm events. Strategies that require a watershed analysis to define site-scale design criteria did not perform better, indicating the efforts of a watershed analysis to develop a SWM strategy are not warranted. Results also indicate that as the capture on an initial volume and duration of drawdown increases, additional benefit does not translate downstream.