Modeling the Response of Runoff in the Delaware River to Changes in Residential Development

Urbanization and associated increases of impervious cover in the Delaware River watershed have been extensive over the past two decades, resulting in a number of water quality impacts, including changes in stream biota. In order to assess the scope of these changes, we mapped the extent of development in the area through time using Landsat and higher resolution imagery and used those data sets to calibrate a spatial predictive model of impervious cover change. Three alternative future scenarios of the counties within the Upper Delaware watershed were developed, working closely with local jurisdictions, and used to simulate future growth consistent with business as usual, rapid growth exceeding current trends, and planned growth emphasizing low impact development. The predictions based on these scenarios provided maps of the probability of development by 2030 at 30m spatial resolution. In order to assess the potential impacts of each future scenario, the maps were used to in a hydrological model to simulate the response of stream flow variables. RHESSYS, a process based hydro-ecological model, was used because it is spatially distributed and explicitly routes overland flow, allowing it to capture changes in landscape connectivity. As expected, greater impervious cover reduced infiltration and baseflow and increased the flashiness of runoff, partly by impacting flow connectivity throughout the watershed. These results will be discussed in the context of future land use and climate change in the region.