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refinements to the proposal, specifically buffer widths. This section describes the basis for the evaluation, <br /> the evaluation process and summary of results. <br /> Basis for Evaluation -Impervious Surface Cover <br /> Riparian areas can enhance water quality in many ways. Riparian areas provide a buffer zone between <br /> upland land uses and water resources, protecting or enhancing water quality, preventing erosion, and <br /> moderating flood flows. Undisturbed, densely vegetated riparian areas trap sediments, inhibit erosion and <br /> filter runoff originating from impervious surfaces, lawns, golf courses, etc. Declines in water quality can <br /> be directly linked to an increase in impervious surfaces, which typically occurs as a result of urbanization <br /> in a watershed. Activities such as road construction, building, land clearing, and grading encroach on <br /> riparian areas and modify the natural drainage patterns. Sedimentation and erosion, although natural <br /> processes, are accelerated in urban areas by increased impervious surfaces. Sediments often carry <br /> nutrients (e.g. phosphates and nitrates) to water resources, excessive concentration of which in the water <br /> can trigger algal blooms, depleting the water of oxygen required by fish and other aquatic organisms. <br /> Sediments also often carry pollutants (e:g. heavy metals, hydrocarbons) to water resources, altering <br /> <br /> - water chemistry. Impervious surfaces also inhibit infiltration. <br /> Determination of existing level of impact, potential water quality function, and feasibility of applying <br /> buffers (Policy team requests #1 and #2 above) was achieved primarily by assessing the extent of existing <br /> impervious surface cover within potential buffer management zones. The use of impervious surface cover <br /> as the primary indicator of waterway health, including water quality, is supported by the research and <br /> findings of the Center for Watershed Protection as described in Site Planning for Urban Stream <br /> Protection (CWP, December 1995). <br /> Evaluation Process <br /> An evaluation was conducted on all water quality protected waterways identified on the Water Quality <br /> Protected Waterways by Protection Criteria map (March 2005), to the Eugene urban growth boundary. A <br /> GIS software model. developed by Lane Council of Governments provided the analysis platform. To <br /> ensure the highest degree of accuracy possible in the analysis, the most recent, up-to-date open waterway <br /> GIS layer ("DOPED was utilized. This data layer incorporated improvements made as a result of recent <br /> field work by PDD and PW staff, in particular to distinguish roadside ditches from other waterways, to <br /> improve the accuracy of information on Goal 5 sites, and to improve the accuracy of information about <br /> water quality protected waterways in terms of waterway existence, location and alignment. For the GIS <br /> model, each water quality protected waterway was delineated by using logical begimling and end points <br /> including: location of discharge to receiving water body, street crossings, and UGB. Tributaries and sub- <br /> tributaries to corridors were delineated separately but with the ability to be included in the overall analysis <br /> of a corridor if needed. Each corridor and tributary was given a unique name and identifying number. <br /> Each corridor, including tributaries, was given a unique "cluster" identification number. This set up <br /> enabled staff to conduct an evaluation of specific data on a corridor, tributary; and even a parcel basis. <br /> Potential buffer management zones were delineated along each water quality protected waterway. <br /> Established based on the Center for Watershed Protection's Site Planning for -Urban Stream Protection, <br /> the delineated buffer management zone has an overall width of 75 feet each side of a waterway and <br /> consists of 3-subzones, each 25 feet in width. The measurement point for determining the innermost <br /> location of the buffer was located either at the center line of the waterway or top-of--bank. In general, for <br /> smaller streams located higher in the drainage system buffer setbacks were measured from center line, and <br /> 3/28/06 2 <br /> _ _ _ <br /> <br />