Quantifying Watershed Susceptibility for Source Water Protection - A GIS Approach

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The Joint Water Commission (JWC) is a collective water supply agency and a primary drinking water supplier in Washington County, Oregon. The JWC’s 228 square mile watershed includes portions of the Tualatin River and Trask River basins. One of the main goals of the JWC’s source water protection efforts is to safeguard drinking water quality by evaluating potential contamination risks within the JWC’s watershed and participating in programs to minimize those risks. The JWC selected GSI Water Solutions to build a source water protection-specific geodatabase and perform specific GIS analysis that would help to quantify potential contamination risks and sensitivity of lands to contamination. GSI was tasked with gathering up-to-date GIS data from various sources that would help to model risk and sensitivity. Once the GIS data was imported into the geodatabase, a risk analysis and a sensitivity analysis were performed. The risk analysis incorporated GIS data related to pesticide applications, agricultural fertilizer applications, potential hazardous contaminant sources, septic tank locations, areas of urban development, and proximity to public roads and railroads. The sensitivity analysis incorporated GIS data related to flood zones, forestry activities, surface water time of travel zones, unstable/vulnerable soils, wetlands, and proximity to surface water. While each of the GIS data used in the risk and sensitivity analysis were informative individually, additional insights about overall risk/sensitivity within the JWC watershed was found by combining the GIS data using the weighted sum geoprocessing method. To accomplish this, GSI worked with the JWC to determine numeric risk/sensitivity rankings and weights of significance to the overall analysis for each layer. Once the rankings and weights determined, GSI used the weighted sum geoprocessing tool in Spatial Analyst to combine the layers to create an integrated, comprehensive view of both risk and sensitivity of lands within the JWC’s watershed. The output of the risk and sensitivity analysis quantified the susceptibility of any location within the JWC’s watershed to contamination based on multiple layers of input. Once watershed susceptibility was quantified, the JWC can better focus program development (saving time and money) to minimize the potential impacts from chemical or biological pollutants. Jesse Manley GSI Water Solutions 55 SW Yamhill St, Suite 300 Portland, OR 97204 503-729-2222 jmanley@gsiws.com

Jesse Manley

Jesse Manley is the GIS manager for GSI Water Solutions in Portland, Oregon. Jesse has been a professional GIS specialist since 2001 and he specializes in GIS solutions for renewable energy, geology, groundwater, water resources, and environmental management. Jesse has been on the NWGIS board of directors since October of 2010 and is co-chair of the 2013 NWGIS Sunriver conference.

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October 17, 2013 - 11:30am - 12:00pm
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