Stormwater quality and quantity were investigated in urbanized catchments in the Pipers Creek watershed in North Seattle in order to characterize existing rates and processes of stormwater runoff in areas of moderate-density residential development. Hydrologic monitoring and water-quality sampling during storm events were performed as part of this project from fall 2002 through spring 2004. Results of the sampling program indicate that concentrations of total and dissolved metals, total suspended solids, nutrients, total petroleum hydrocarbons, pesticides, herbicides, and E. coli and fecal coliform bacteria present in the runoff from these areas are significant, especially because they represent only a fraction of the total pollutant loading experienced by the receiving stream. Detailed analysis of heavy metal concentrations, total suspended solids concentrations, and concentrations of solids in the clay and silt size ranges has allowed for better understanding of how solids and metals interact in an urban stormwater environment. This research highlights the importance of mitigating the impacts that urban development has had on the runoff from these catchments, given the regional goal of improved instream aquatic conditions for native biota, particularly salmon. This research is part of the City of Seattle's Natural Drainage Systems project, which has been responsible for several stormwater management projects already constructed within the Pipers Creek watershed. As additional projects are implemented in the coming years, results from this research will allow for a comparison of pre- and post-improvement stormwater runoff conditions. This should document the effectiveness of these various stormwater management techniques on alleviating the effects of urbanization, both in the catchments themselves and on downstream natural systems.
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