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I I I I I I I I I I I I I I I I I I I flows in the river from the 10 percent exceedance flow to the 90 percent exceedance flow. The 10 percent exceedance flow is 11,000 cfs and the 90 percent exceedance flow is 600 cfs. The water surface elevations resulting from the two design flows in the river were determined from the HEC-2 modeling performed by FLO Engineering. Sheet 13 in Appendix C is from the Concept Development Report and shows the locations of sections used by FLO engineering in the hydraulic modeling. Sec. 400.06 is approximately the location of the bypass outlet. The HEC-2 model was re-run for the 11,000 cfs and the 600 cfs flows. Sheets 14 and 15 in Appendix C show the water surface profiles in the river for the 11,000 cfs and 600 cfs flows. Sheet 16 shows a plot of the river cross section at Sec. 400.06. The water surface elevation for the 11,000 cfs flow is El. 4677.8 and for the 600 cfs flow is El. 4670.5. It is recommend that staff gages be set or periodic water surface elevations be surveyed to verify these elevations. The results are completely dependant on the hydraulic modeling prepared by FLO engineering. Changes in the river cross section or other conditions may have occurred since the time of the original data that may alter water surface calculations. The water surface elevations in the river are used as tailwater elevations in the design of the bypass pipe. The pipe will be assumed to be made of either PVC or HDPE material. The computer program CulvertMaster is used in the analysis of the bypass pipe. A 44 cfs flow for these conditions will require a 48 inch diameter pipe. Sheets 17 and 18 in Appendix C show the results of the pipe analysis for the 11,000 cfs and 600 cfs flows in the river. A complete profile of the flow through the bypass system for the 10 percent exceedance flow and the 90 percent 25