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Comments on the River Road / Santa Clara Stormwater Basin Master Plan from the Santa Clara Community Organization. Therese Walch Eugene Public Works 99 E. Broadway, Suite 400 Eugene, OR 97401 October 23, 2009 This basin master plan for River Rd/Santa Clara is an opportunity to use all the "tools" in the toolbox to best protect the open waterways, maximize storm water conveyance through these channels, and accommodate future densification without sacrificing what makes the RR/SC neighborhoods unique. While this plan touts some new ideas in the use of rain- gardens both along streets and in neighborhoods, it misses the mark in recognizing the existing natural infrastructure and prioritizing its protection and enhancement. The cost of manufactured infrastructure that degrades over time versus the protection of existing natural infrastructure that improves over time is not something we can afford, and is not the wisest use of what we have. This plan falls short of its aspirations to "provide a management strategy for storm water that reflects the uniqueness of the RR/SC basin ". Our hydrology is not what makes us unique. The forms and patterns created by heritage trees, waterways, prime soils, agricultural operations, significant populations of both urban and rural and county and city residents and all they bring to their neighborhood is what makes us unique. Without taking into account these factors, this plan has no chance to meet its goal of planning reflecting that uniqueness. The major difference between this basin and others throughout the city is our lack of storm water infrastructure and our extensive network of open waterways. These waterways, both large and small, are the infrastructure that makes development possible. They are also our primary defense from flooding. To date, many of the "lesser" waterways in our area have not been mapped and merit no level of protection from filling by development. These swales and watercourses, not wet much of the time, are what protect the existing older development from high water events. As larger lots on these swales are divided and infrll development happens, the swales are not identified as part of a complete stormwater system and are instead deemed "depressions" in otherwise developable land and filled. There is no recourse for the existing residents along what was a continuous watercourse that now ends at their property line. The neighbor's fill has increased their risk of inundation. There is a need for these watercourses to be mapped and protected from filling. Developers in our area view them as impediments to the "clean slate" they like to use when mapping their subdivision. We see them as an opportunity for the developer to design around their own use of them to accommodate the increase in stormwater their development will ultimately bring while maintaining the natural infrastructure that protects all of Santa Clara and River Rd. In this way, there is a direct benefit for the developer to use them and save on manufactured infrastructure costs. To date our basin has a total impervious surface area of approximately 37.5 %, and is projected in this plan to reach 51% at buildout. This will be the highest projected percentage of impervious surface of any of the city's basin areas. This plan highlights how impervious surface area affects both water quality and flood control profoundly. Water quality: Research shows that "water quality degradation occurs at relatively low levels of imperviousness (10 -20 %), so the implications of development on water quality are significant" (p.2 -23). Flood control: The computer model used to predict water levels did not match actual observed levels. Model parameters were adjusted to try and make the model more closely resemble actual conditions. Then several "additional model runs were conducted to evaluate the model's sensitivity to changes in input parameters. The results of these sensitivity analyses indicated that the impervious percentage area was the most sensitive model input parameter. "(p. 3 -6) So, with impervious surface percentage being the most influential variable, this basin projected to have the