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I I I I I I I I I I I 1 I I I I 1 I; I screens will be El. 4681.0 - El. 4677.0 = 4.0 feet. Sheet 21 in Appendix C shows the calculations for screen size assuming 4 feet depth of flow through the screens. Selected for this option are 25 screens, 14 feet long by 6 feet tall. Assuming panel support columns with a 12 inch flange width, the center to center spacing of the columns will be 15 feet. Using 25 panel bays, 15 feet on center, the length of the screen structure will be 375 feet. The height of the structure was sized to not overtop up to the 50-year flood water elevation. Table 3.1 on page 7 of the Concept Development Report shows the 50-year flood flow to be 44,400 cfs. Figure 4.3a on page 22 of the Concept Development Report shows a water surface elevations for a flow of 44,400cfs of approximately El. 4689.0. The top deck of the screen structure will be set at El. 4690.0. The length of the screens required are set by the minimum flow depth of 4 feet. The screen panel height was set at 6 feet. The top of the screens will be at El. 4677.0 + 6' = El. 4683.0. Steel bulkhead panels 7 feet tall will be installed in the guides above the fishscreen panels to block the flow above El. 4683.0 up to El. 4690.0. A brush type cleaner will be used to remove small debris from the screens. The depth from the top deck of the structure to the base of the screens will be 13 feet. This is a fairly long reach for the brush cleaner. For this reason, it is recommended to use an Atlas Polar type of mechanized brush cleaner. The total length the brush will sweep is 375 feet. If the brush were traveling at 2.0 feet per second, the travel time for one sweep would be 187.5 seconds, and one sweep cycle would be 375 seconds, or 6 minutes 15 seconds. To allow a shorter cycle time and redundancy in the cleaning system, it is recommended to use two Atlas Polar brush cleaner units. 19