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(3) The ladder is offset from the existing sluice • gates approximately 15 feet. The west side edge of the ladder is located to accommodate the upstream trashrack, auxiliary evater piping, and the diffuser. Preliminary computations for Alternate No. 1 show that offset- ting the ladder from the sluice gates reduces high velocities near the west ladder entrance. (4) The bottom of each vertical slot and orifice is flush with the ladder floor, so that these "bottom swimmer" species are not required to avoid obstacles. However, the circulation of flow in the ladder pools may not behave as expected. The development of most vertical slot ladders is based on model studies using 8-foot-wide by 10-foot-long pools. So when the ladder pools are reduced to 8 feet wide by 5 feet long, the flow through the slot may "short-circuit" from one slot to the next downstream slot. With this flow pattern, energy may not 6e dissipated in the pools and flow could become excessively turbulent. If problems occur, field adjustments in the ladder should alleviate any undesirable flow patterns. Field adjustments could include the use of a small sill at the bottom of the slot and/or an addition of a directional wing downstream of the slot. See Plate 12 for positioning of sill and/or directional wing with respect to the vertical slot. Also, orifices may need to be closed if satisfactory flow patterns are not attained. (5) This ladder configuration has potential of forming a much larger gravel bar downstream from the ladder structure than Alternate No. 1. The bar would be larger because this alternate blocks a longer portion of the spillway than Alternate No 1. This larger bar may eventually block passage to the east fish entrance unless the area was dredged periodically. b. Impacts. (1) Impacts Affecting RWPC. (a) To attain desirable fish attraction condi- tions, RWPC may be asked to slightly modify their standard operating procedures. During high spring flows, releases of flow through the existing sluice gates should be regulated for the best fish attraction conditions. Flow from the sluice gates should not create a velocity barrier at the west fish entrance during the migration season. Also, as flashboards are installed on the dam crest, their placement should start at the right bank (looking downstream) and progress toward the left bank. This should keep the attraction flow, created by spilling of water over the crest, near the fish ladder. • 20