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SECTION 2 Study Area Characteristics calculations for this data are available from the City of Eugene.] The majority of this impervious surface area is concentrated between Highway 99 (west) and the east boundary of the basin. Map 3 depicts the existing generalized impervious surface area in pink. Due to the map scale and data restrictions, developed lots are shown entirely in pink. These pink areas are a mix of impervious surface and pervious surfaces associated with the land use such as lawns, streetscapes, parking lot planting, and other landscaped areas. Assuming that future growth in the basin will follow conventional stormwater management drainage practices and will develop according to the land use categories depicted on the Eugene - Springfield Metro Plan designations (see Map 2), the amount of impervious acres in the UGB portion of the basin is projected to increase to 3,044 acres, or 50 percent of the basin's UGB area at buildout. [Note: calculations for this data are available from the City of Eugene.] 2.3.3.2 Pervious Surfaces Except for the impervious surface areas noted above, the rest of the basin remains in a pervious condition, consisting mostly in the form of prairie wetlands, forest, agriculture and lawns. Overall, pervious area cover is expected to decrease from the current 62.5 percent of the UGB portion of the basin (3,794 acres) to 50 percent (3027 acres) at UGB buildout. For the purposes of this report, pervious surface areas were identified and grouped into Forest Cover, Landscaping, and Other Vegetated Areas (refer to Figure 2 -4) for the following reasons: Forest Cover is highly effective in reducing runoff volumes, and in preventing erosion (e.g., reduces soil impact by slowing down the velocity of precipitation and by intercepting up to 35 percent of it before hitting the ground) and stabilizing steep slopes (established root zones). Areas were included in this category if the forested area exceeded one acre in size. One percent of the River Road Santa Clara basin is currently in forest cover and at UGB buildout, forest cover would decrease to 0 percent. Landscapin areas, including lawns, streetscape and parking lot landscaping are associated with site improvements due to urban development. This category was distinguished to highlight both its positive and potential negative impacts on stormwater resources and is included in the area shaded pink on Map 3. Positive impacts include protection of surface soils, filtration of sediments, and some infiltration (although this is reduced from pre - development conditions). The use of chemical fertilizers, pesticides, and herbicides can cause negative impacts to water quality. The amount of landscaped area in the UGB is projected to decrease from the existing 41 percent to 39 percent at UGB buildout. • Other Vegetated Areas are pervious surfaces not in forest cover or landscaping use, such as agricultural fields, pasture, vacant lots, prairie wetlands, and small clusters of trees (less than one acre). Similar to the landscaping category, these areas have both positive and negative impacts on stormwater resources. Agriculture and pasture uses can be significant contributors of pollutants in this category due to the use of chemical fertilizers, pesticides, 0:\25695978 Eugene RR -SC Final Basin P1an\Master P1anTINAL 2- 2010\Master_Plan 3- 11- 10_FINAL_ Word _Version.doc 2-12