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Using a watershed-centric approach to identify potentially impacted beaches
Citation:
Murphy, M. S. AND E. A. SAMS. Using a watershed-centric approach to identify potentially impacted beaches. Presented at ESRI International User Conference, Saan Diego, CA, August 04 - 08, 2008.
Impact/Purpose:
research results
Description:
Beaches can be affected by a variety of contaminants. Of particular concern are beaches impacted by human fecal contamination and urban runoff. This poster demonstrates a methodology to identify potentially impacted beaches using Geographic Information Systems (GIS). Since healthy recreational waters depend almost entirely on the activities upstream, a watershed-centric protocol was developed. Point-in-polygon analysis was performed to count the number of wastewater treatment plants (WWTP) and aggregate total effluent discharge (million gallons/day) to the sub-watershed (HUC10) level. Urban areas were mapped and a critical population threshold set at 12,818 – the mean population for urban areas in Puerto Rico. Beaches were analyzed for their proximity to high-volume watersheds and urban areas above the population threshold. Because the collocation of contaminants from both sources (WWTPs and urban runoff) can confound water quality researchers, an attempt was made to distinguish between beaches that were potentially impacted by urban runoff and those potentially impacted by sewage discharge. Beaches were categorized based on the following criteria: • Non Urban WWTP – beaches that bordered a watershed with a total effluent discharge ≥ 1mg/d, but were at least 2km from a significant urban center (pop. > 12,818) • Urban WWTP – beaches that bordered a watershed with a total effluent discharge ≥ 1mg/d and were within 2km of a significant urban center. • Non-WWTP (i.e. urban runoff) – beaches that bordered a watershed with a total effluent discharge of ≤ 1mg/d, but were within 2km of a significant urban center. The spatial and tabular output produced by this methodology can be used in conjunction with ancillary data as decision-making tools to select beaches that may be good candidates for water quality and human health research. Additionally, the mapped output from this pilot project can be used interactively in the field using the GPS interface in ArcMap. National Hydrography Dataset and WWTP data were downloaded from EPA’s Reach Address Database. Digital orthoimagery quarter quadrangles were provided by EPA Region 2. Beach location and visitation data were provided by the Puerto Rico Environmental Quality Board and EPA Region 2. TeleAtlas urban area boundaries and population were provided by EPA’s Office of Environmental Information.