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SECTION 3 Flood Control Euaination 9. Channel roughness coefficients (for open channels). For the River Road Santa Clara basin, the model was used to evaluate the capacity of approximately 160 open waterway and pipe segments under existing and future land use conditions. Table 3 -2 (provided at the back of this section) provides the major hydraulic information for each of the modeled conduits in the 4 major subbasins evaluated within the River Road Santa Clara basin. Specifically, the table provides the information for parameters 1 — 6 listed above, in addition to the drainage area for each conduit, the relevant design storm, and the model results for the relevant design storm. Model results are presented in terms of peak flows and maximum water surface elevations. The results for all storm events that were run through the models (i.e., 10 -year, 25 -year, 50 -year, and 100 -year storms) can be found in Appendix B. As discussed previously, due to the multi jurisdictional ownership of the drainage system, the City did not have a comprehensive data set on the drainage system in this basin at the time the original River Road Santa Clara Basin Plan was completed. Since the original Plan was completed in 2002, the City and County partnered to develop this revised Plan, and the following areas were surveyed and updated in the original model, resulting in a more refined hydrologic and hydraulic data set and a more refined modeled system. A more detailed summary of major changes made to the model is provided in Appendix G. The refined model results were used for design of the capital projects described in Section 3.5. Willamette Overflow major subbasin: — A large elevation difference was noted between the inlet and outlet pipes to the manhole at node 58287, located east of River Road and north of Division on Figure 3 -7. Hydraulic conditions at this location were field verified and surveyed. — The pipe system that conveys stormwater from Beltline Road to the Willamette Overflow drainage system, as shown on Figure 3 -7, appeared to include pipes with a diameter equal to or greater than 36 inches, which would ordinarily be included in the model, but insufficient data were initially available for these pipes. Hydraulic conditions at this location were field verified and surveyed. — Field crews noted that fill had been placed in the open waterway between Division and Hunsaker, which blocks the waterway except under high flow conditions. This fill was not reflected in the original survey data so a revised survey of this open channel segment was conducted. • Flat Creek major subbasin: — The hydrologic connection of subbasin FC -070 and Flat Creek was field verified. • A -I Channel major subbasin: — Hydraulic conditions in the pipe system along Irving Road that conveys stormwater to the A -1 Channel, shown on Figure 3 -7, were unclear, and therefore the system was field verified and surveyed. — Drainage patterns in the A -1 Channel major subbasin, south of Beltline Road on Figures 3 -7 and 3 -8 were unclear. A number of drywells may result in less area that is directly connected with the A -1 channel. Hydrologic conditions at this location were field verified. 0:\25695978 Eugene RR -SC Final Basin P1an\Nlaster P1anTINAL 2- 2010\Master_Plan 3- 11- 10_FINAL_ Word _Version.doc 3-5