Spatial Translation and Scaling Up of Low Impact Development Designs in an Urban Watershed

The downstream impacts of best management practices designed to manage stormwater at the source are not well documented. This study investigated two aspects of the hydrologic effects of low impact development (LID) practices at the watershed scale by examining the potential watershed benefits of the scaling up of LID designs, and evaluating the downstream effects of the spatial translation of LID designs within a watershed. PCSWMM was used to model long term runoff reduction with the implementation of LID practices in Deer Creek watershed, Missouri. The model was calibrated from 2003 to 2007 (R-2 = 0.58 and NSE = 0.57), and validated from 2008 to 2012 (R-2 = 0.64 and NSE = 0.65) for daily direct runoff. The calibrated model was used to simulate a baseline scenario for the study period, 2003 to 2012 (NSE = 0.61; R-2 = 0.63), for comparison to LID scenarios. The baseline and all LID scenarios were developed based on the 2006 land cover map of the National Land Cover Database. A pre-development scenario was also developed with historical land cover to assess the ability of LID practices to restore pre-development hydrologic conditions. Results showed an increased runoff reduction, from 3% to 31%, with increased implementation levels (from 25% to 100%). As the spatial extent of LID practices increased, runoff reduction at the watershed outlet also increased, ranging from 3% to 19%. When LID implementation was moved from one location to another in the watershed, simulation results revealed that an optimum location for placement of stormwater management practices was near the outlet for the study watershed, with a reduction in runoff ranging from 1% to 4%. This study also showed that LID practices could be used to restore pre-development hydrologic conditions. The optimal location for LID practice implementation in this watershed appears to be near the outlet. Additional studies are however needed to better understand the optimum location for placement of stormwater management practices within a watershed.