PREDICTING INFLUENCES OF URBAN DEVELOPMENT ON THERMAL HABITAT IN A WARM WATER STREAM

Water temperatures can become elevated in urbanized systems, indirectly harming fish by lowering DO levels and/or increasing contaminant toxicity. Elevated water temperatures occur due to increased solar input from channel widening, reduced vegetative shading, reduced base flow, and thermally enhanced runoff. Using data from the Back Creek watershed in southwestern Virginia, the thermal effects from urbanization were modeled, and the implications for the fish community were considered. Back Creek is a 42-km second-order, warm-water tributary to the Roanoke River. Hydrologic changes resulting from urbanization were modeled using the Hydrologic Simulation Program Fortran in combination with the Stream Network Temperature Model, each of which is described. A number of scenarios, which are described, were considered. Results indicated that the alterations to flow by low-density development did not raise temperatures. However, the magnitude of the predicted thermal change was greater under multiple urbanization effects than under single effects. An increase in impervious surfaces to 15% increased water temperatures by about 1 degree C, which would not limit the fish community from the standpoint of upper thermal limits, but could reduce growth, induce stress and disease, or impair reproductive capabilities.