From Urban to Suburban: Evaluating the Effects of Impervious Surfaces on Cobbs Creek and Darby Creek
Urban streams face a multitude of environmental issues today. Land cover change and anthropogenic pollution threaten urban streams and the ecosystems and the human populations they support. One of the biggest obstacles facing urban streams is the overbearing presence of impervious surfaces like roads and sidewalks, which lead to more stream runoff, more polluted runoff, and more severe flooding events detrimental to the health of already-fragile ecosystems. As a part of Dr. Jane Dmochowski’s Urban Vegetation Community-Based Participatory Research Project (UrbVeg CBPR), this research will assess the relationships between land cover, vegetation density, and hydrological trends in two Philadelphia watersheds: Cobbs Creek and Darby Creek. Because the Darby Creek watershed contains significantly less impervious surface cover, it is used as a baseline against the much more urbanized Cobbs Creek watershed.
The main hydrologic impacts from urbanization being investigated are peak discharge and the lag time. The lag time is the time between peak precipitation and peak discharge in a stream. Longer lag times are usually indicative of healthier watersheds, with plenty of permeable land cover to allow precipitation to percolate through the earth. This research attempts to analyze the relationship between permeable surface cover and lag time in the Cobbs Creek watershed. Through remote sensing and hydrologic modeling, this research project attempts to assess the hydrologic that impervious surfaces have on nearby urban rivers and streams. According to models run, the Cobbs Creek watershed does display higher peak discharge and shorter lag times in response to precipitation events, as predicted. This is most likely caused by the greater cover of impervious surfaces.