Kevin P. Rhoads, Katherine L. Meierdiercks, Nicholas F. McCloskey, Michele Golden, Mary Beth Kolozsvary
The processes that control runoff quantity and quality in urban watersheds are complex and not well understood. While impervious surface coverage has traditionally been used to examine altered hydrologic response in urban watersheds, several studies suggest that other elements of the urban landscape, particularly those associated with urban infrastructure and the drainage system play an equally important role. The relative importance of impervious surfaces, stormwater ponds, expansion of the drainage network, and drainage network structures in controlling hydrologic response was examined in the subwatersheds of the Kromma Kill, an urban watershed located in Albany County, NY. In this study, Geographic Information Systems (GIS) was used to compute geospatial landsurface and drainage network properties of five Kromma Kill subwatersheds. In these same subwatersheds, water quantity (rainfall and runoff) and quality [macroinvertebrates, nitrate (NO3-), total nitrogen (TN), dissolved oxygen (DO), total dissolved solids (TDS), and non-purgable organic carbon (NPOC)] parameters were measured. Strong and significant correlations were identied between landsurface and drainage network properties and field observations. Causal relationships were then tested using the EPA SWMM stormwater model. Field and model analyses suggest that while percent imperviousness is a dominant control on water quality, drainage density and slope are equally important. However, for water quantity, while imperviousness is positively correlated with increased runoff volumes, drainage network properties and slope are the dominant controls on runoff volumes. Results have important implications for stormwater management plans, especially those aimed at reducing the effective impervious surface coverage of urban watersheds. Reducing the percentage of effective imperviousness in a watershed is not a “one size fits all” solution and can help to meet some management objectives such as reducing nitrogen concentrations and improving water quality, but may not serve as the most effective, and therefore economical, solution for every management objective including reducing runoff volumes.
