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3. Operational Flexibility. a. The number of fish ladder weirs can be reduced to 11 weirs, which form 8-foot-wide by 20-foot long pools. The result of this modified design is a 1-foot head drop per pool. For this operational condition, the total ladder flow is approximately 25 cfs and the available auxiliary flow is 75 cfs. At high riverflows (6,000 cfs), the head drop will gradually vary from 0.4 foot at the downstream end of the ladder to 1.0 foot at the upstream end of the ladder and ladder flow will be 31 cfs. b. The number of fish ladder weirs can also be increased to 45 weirs, which form 8-foot-wide by 5-foot-long pools. The result of this modified design is an approximate head drop of 0.25 to 0.35 foot per pool. For this operational condition, the total ladder flow is approxi- mately 15 cfs and the available auxiliary flow is still 75 cfs. At high riverflows, the head drop will gradually vary from 0.15 foot at the downstream end of the ladder to 0.25 foot at the upstream end of the ladder and the ladder flow will be 18 cfs. c. Refer to Table 1 for ladder flows, slot and orifice velocities, and head drop per pool. 4. Other Considerations. a. Biolo4ical and Technical Considerations. (1) The two target species prefer swimming close to the river bottom. At the fishway entrances, fish can remain near the river bottom and swim through the side-opening slide gates. These gates can be adjusted to achieve the desired head drop at the entrance and the gate opening will be flush with the invert elevation of the entrance at 4,560.0 feet. (2) The fish ladder is positioned so that fish migrating up the main channel of the river will be attracted to the sluice gate discharge. These fish would most likely locate the west and downstream entrances. Fish migrating up the right bank will be stopped by the obstruction of the dam. They should locate the east entrance by swimming across the downstream face of the dam searching for upstream passage. The entrances are also positioned downstream of the existing concrete spillway apron. At low flows, the spillway apron could possibly become a velocity and depth barrier to migrating fish. • 19