Impacts of Development Pattern on Urban Groundwater Flow Regime

We compare the effects of urban development type and spatial pattern on the hydrology of six small headwater catchments near Baltimore, Maryland, utilizing a three-dimensional coupled groundwater-surface water-land atmosphere model (ParFlow.CLM). The catchments range in size from 0.2 to 2 km(2), across a spectrum of older heavily urbanized development to less developed exurban residential areas. The topography and land cover of each model domain are defined using high-resolution LiDAR topography and orthoimagery. Simulations were conducted at an hourly time step for calendar years 2012-2015 using a 10-m terrain-following horizontal grid with variable dz (0.1 to 8 m). Differences in development type and pattern across catchments give rise to complex spatial and temporal trends in the water budget. Catchments with the lowest amounts of impervious cover show the greatest variability in total storage response to climatic variation, whereas those with the greatest amount of impervious cover show less variability in response of subsurface storage to annual and seasonal variability in precipitation input. The storage response among catchments tends to be pronounced during prolonged dry and wet periods, with the variability in response being less pronounced over short-term events. A negative correlation is observed across catchments between impervious cover and net subsurface storage variability. Temporal variability in subsurface storage is most responsive to development pattern in near-surface layers, but transitions to topographic control at depth. Spatially, the development footprint controls where recharge and evapotranspiration occur in the unsaturated zone. Infiltration in pervious areas flows laterally beneath impervious surfaces.