Urban Residential Surface and Subsurface Hydrology: Synergistics Effects of Low-Impact Features at the Parcel Scale

Accurately predicting the hydrologic effects of urbanization requires an understanding of how hydrologic processes are affected by low-impact development practices. In this study, we explored how growing season surface runoff, deep drainage, and evapotranspiration on a residential parcel are affected by several low-impact interventions, including three impervious-centric interventions (disconnecting downspouts, disconnecting sidewalks, and adding a transverse slope to the driveway and front walk), two pervious-centric interventions (decompacting soil and adding microtopography), and all possible holistic combinations. Results were compared to both a highly and moderately compacted baseline parcel under an average and a dry weather scenario for a temperate climate. We find that under reasonable assumptions for highly compacted soil, pervious areas are a major source of runoff and disconnecting impervious surfaces may be relatively less effective without improving soil conditions. Under both highly and moderately compacted soil conditions, combining efforts to decompact soil with impervious disconnection has a synergistic effect on reducing surface runoff and increasing deep drainage and evapotranspiration. All combinations of interventions enhance infiltration, but the partitioning of additional root zone water between deep drainage and evapotranspiration depends on the weather scenario. Importantly, when all low-impact interventions are applied together, growing season deep drainage is higher than that from a vacant lot with no impervious surfaces. We infer that ecohydrologic interfaces between impervious and pervious areas are strong controls on urban hydrologic fluxes and that high-resolution, process-based models can be used to account for these interfaces and thereby improve predictions of the hydrologic effects of low-impact interventions.