WATERSHED MODELING IN URBANIZED METROPOLITAN BALTIMORE

To best manage water in urban areas we need to understand the effects of urbanization on the hydrologic cycle. We present results from a regional water sustainability project in the Baltimore region. We are using ParFlow, a fully-coupled three-dimensional, finite-difference watershed model with variably saturated subsurface and surface flow. Here we present applications of ParFlow to date at two scales: (1) the Gunpowder-Patapsco basin, which encompasses much of the Baltimore metropolitan region (13,200 sq km domain size), and (2) Dead Run, a small highly urban watershed embedded within the Gunpowder-Patapsco watershed, at the edge of Baltimore City (72 sq km domain size). At the smaller Dead Run scale, the model, and particularly the overland flow component, was highly sensitive to landscape form and urbanization. We found that enforcement of topographic slopes to follow channels was necessary as the topography alone was not adequate to define the drainage in this flat, urban domain. Furthermore, we found including some individual piped streams— features that do not register on any Digital Elevation Model (DEM)— was required for the domain to drain properly. Elevations from a DEM in an urban landscape may not be able to adequately define surface flow paths as streams may have been moved, channelized, piped underground, or otherwise modified. We also are quantifying human modifications of the water balance in urbanized watersheds, including water distribution pipe leakage, infiltration and inflow, and water withdrawals from reservoirs. In future work, this watershed model will be coupled to an urban growth model (SLEUTH) of the Baltimore metropolitan region to explore the feedbacks between water availability and future development.