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SECTION 3 Flood Control Euaination In order to identify flood related problems and opportunities, a flood control evaluation was completed for the drainage system in the River Road Santa Clara basin that is described in Section 2.5 and illustrated on Map 5. A computer model was used to predict capacity deficiencies in the existing storm drainage system. Section 3.1 provides a brief description of the computer model and a summary of the hydrologic and hydraulic model input data. Section 3.2 describes the model validation process, and Section 3.3 provides a description of model results. Section 3.4 provides a general description of the identified flood - related problems. Section 3.5 describes the project alternatives and development standard alternatives that were selected to address the identified flooding problems. 3.1 Hydrologic/Hydraulic Model Development To develop a flood control strategy for the River Road Santa Clara basin, a computer model was used to evaluate hydrologic /hydraulic conditions of the public storm drainage system. The storm system was evaluated under both existing and buildout land use conditions. The City of Eugene selected the XP -SWMM model software to conduct these analyses. In general, the evaluation concentrated on the conveyance capacity of the significant components of the public drainage system; typically, all storm sewer pipes with a diameter equal to or greater than 36" and the associated open waterways on the Willamette Overflow (also referred to as the East Santa Clara Waterway), Spring Creek, Flat Creek, and the A -1 Channel. The River Road Santa Clara basin drainage system, including pipes, open channels and drywells, is shown on Figures 3 -2 through 3 -8. Figure 3 -1 provides an index map that illustrates the relative locations of Figures 3 -2 through 3 -8 in the basin. Modeled drainage segments and locations of the proposed capital projects are also illustrated on Figures 3 -2 through 3 -8. The City -wide storm drainage basin planning summary in Volume I contains detailed information regarding the process and sources of information that were used for identifying flooding problems and opportunities. Section 3 of Volume I specifically includes detailed information regarding the following: • Model selection process. • Sources of model input data. • Design storm selection process. • Model calibration (note: while Volume I contains calibration information that was applied City -wide during the development of the 2002 basin plans, a separate model validation was conducted that is specific to the River Road Santa Clara basin and is described in Section 3.2 of this plan). This section of the River Road Santa Clara report provides a summary of the basin specific hydrologic and hydraulic data used in the models. 3.1.1 River Road Santa Clara Basin Hydrologic Data The original River Road Santa Clara Study was an initial study towards development of a stormwater basin master plan and was created in 2002. The Study identified a number of 0:\25695978 Eugene RR -SC Final Basin P1an\Nlaster P1an\FINAL 2- 2010\Master_Plan 3- 11- 10_FINAL_ Word _Version.doc 3-1