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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Bynass Pille Desi~ <br /> <br />After reducing the flow in the bypass by the secondary screens, a residual 10 cfs flow will <br /> <br />remain. The fish will remain in this flow and be diverted back to the river using the same bypass <br /> <br />alignment as was discussed for Alternative 1. Using the same water surface elevations for the 10 <br /> <br />percent and 90 percent exceedance flows as were discussed for Alternative I, the program <br /> <br />CulvertMaster was used to analyze the pipe. For the 10 cfs flow, a 24 inch diameter pipe is <br /> <br />required. Sheets 19 and 20 in Appendix C show the results of the bypass pipe analysis. The <br /> <br />profile through the bypass for this alternative will be very similar to that shown on Figure 9 in <br /> <br />Appendix B, except a 24 inch bypass pipe will be used. <br /> <br />Review of Options <br /> <br />The first decision to be made should probably be a selection between either a true screen <br /> <br />structure (flat plate or rotary drum) or a louver structure. The most important advantage of a true <br /> <br />screen structure is that a properly functioning screen system will provide an almost 100 percent <br /> <br />exclusion of both adult and juvenile fish. The same is not true for a louvered structure. A louver <br /> <br />screen is not a good name because the device does not physically prevent entry of fish into the <br /> <br />canal, it merely discourages entry. A louver is actually a type of behavior modification device <br /> <br />whereby fish are diverted away from the louvers and guided to the bypass. Data as to the <br /> <br />efficiency of louvers for the species of concern at this site is not available. Some studies <br /> <br />regarding louvers for the protection of salmon are available. One report, Use of Louvers for <br /> <br />Downstream Migrant Protection, is included in Appendix F. The report states the expected <br /> <br />efficiency to be 40 to 95 percent depending on fish species and life stage or size. <br />27 <br />