Baltimore Ecosystem Study Institute of Ecosystem Studies

2016 BES Annual Meeting Presentation and Poster Abstracts

Simulating impacts of urban development on water budgets in headwater catchments in the Gwynns Falls watershed using ParFlow.CLM
Barnes, Michael
Co-Authors: Claire Welty, Andy J. Miller

Abstract: We carried out 3-dimensional coupled atmosphere-land surface-surface water -groundwater simulations using ParFlow.CLM to quantify the complex effect of urban development on overall catchment water budgets. Here, we compare results from 6 sub-basins (0.2-0.6 sq km in area) of the Gwynns Falls watershed characterized by varying percentages of impervious cover and types of urban development ranging from 1960s residential to 1990s mixed residential-commercial. Simulations were conducted using 10-m horizontal gridding with variable vertical discretization (0.1 m to 8 m) at an hourly timestep for the period of 2012-2015. This enabled comparison of seasonal and event-based changes in runoff, storage and evapotranspiration (ET) at high spatial and temporal resolutions. Seasonal trends in storage across the 6 basins indicate that impervious cover reduces the overall variability in subsurface storage by reducing infiltration, while also reducing ET. Long-term spatial variability in model pressure data delineates areas in the unsaturated zone where recharge and withdrawal from storage is restricted by the urban footprint of impervious surfaces. Hurricane Sandy in October 2012 provided an opportunity to compare storage dynamics in response to a long-duration, steady rain event. Mapping subsurface storage differences across the landscape shows how infiltration is restricted in the soil zone beneath impervious cover, and the response of the underlying saturated storage zone. Storage changes in response to Sandy were of the same order of magnitude as inter-seasonal changes in storage seen over the simulation period.