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. "~ 3 . . '. . . . . . . I I . . I . . I But these are costly improvements. Moreover the depressed local economy and the uncertainty of funding from State and Federal Government sources has placed these large-scale improvements on some future agenda. In the meantime, effective smaller-scale less costly solutions must be developed to mitigate the impacts on the Ditch from: (a) very recent development, (b) contemplated future development such as street improvements in areas served by the Ditch, and (c) possible future annexations. Evaluation For Near-Term Improvements This report presents results from a system-wide evaluation of recent and near-term storm runoff impacts on the Pioneer Drainage Ditch and mitigation of these impacts. The evaluation includes: An update of the baseline hydrology and hydraulics of the system presented in Leaf and RCI (1983). A determination of the increases in flow above baseline levels that will result from future street and drainage improvements, potential developments by the private sector, and future annexations. A determination of the most cost-effective alternatives for mitigating these impacts consistent with the Master Drainage Plan. These alternatives include both preventive and structural controls such as local ditch improvements, ahd both on-site and off-site detention storage. HYDROLOGY AND HYDRAULICS Most of the technical information on the hydrology and hydraulics of the Pioneer Drainage, Ditch system is contained in Leaf and RCI (1983). These data were used in preparing this report as well as updated estimates of runoff volumes and peak flows for existing and future development conditions. Existing Conditions The assumed watershed area which generates local storm runoff intercepted by the Pioneer Ditch is shown in Figure 2. Five control nodes were