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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 />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 ("DOPEN) 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 Goa15 sites, and to improve the accuracy of information about <br />water quality protected waterways in terms of waterway existence, location and alignment. Forthe GIS <br />model, each water quality protected waterway was delineated by using logical beginning 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 (Page 8 updated 4/4/06) 2 <br />