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based on a reasonable design low flow of 300 cfs below the dam, which is • 50-percentile expected flow for August (refer to Appendix B for hydrolo- gic information). The fish ladder entrance was then set at 4,560.0 feet elevation to maintain a 3-foot minimum pool depth. Using the low tail- water elevation and an upstream water surface elevation of 4,575.0 feet, the change in water surface elevation from below to above Redlands Diversion Dam is approximately 12 feet. The upstream water level of 4,575.0 feet elevation is the desired minimum water depth maintained by RWPC. The basic design of the ladder uses the biological and technical criteria of 8-foot-wide, 10-foot-long, 3-foot-deep pools; 0.5 foot of head drop per pool; 1-foot-wide vertical slot; and 1-foot-wide by 1.5- foot-high orifice (slot and orifice inverts placed flush with the ladder floor). With 0.5 foot of head drop per pool and water surface difference of 12 feet (at low tailwater), the ladder has 23 vertical slot/orifice weirs and one drop in water surface elevation at the slide gate fish entrance. For this operational condition, total ladder flow is approxi- mately 18 cfs. b. The reasonable design high flow was chosen as 6,000 cfs passing over the spillway,. which is approximately the 80-percentile expected flow for May. At the higher flows, the location of this fish ladder reduces the original design capacity of the spillway. The con- sequence of this reduced capacity is a higher forebay water elevation of approximately 4,575.5 feet. From preliminary computations, tailwater was calculated as elevation 4,567.0 feet. The change in water surface eleva- tion from below to above the dam is then approximately 8.5 feet. With the basic ladder design (23 weirs, 8-foot-wide by 10-foot-long pools) and accounting for the backwater effect into the ladder, the head drop will gradually vary from 0.2 foot at the downstream end of the ladder to 0.5 foot at the upstream end of the ladder. For this operational condition, the total ladder flow is approximately 20 cfs. c. For flows above 6,000 cfs and below 8,000- cfs, the ladder should be closed at the forebay entrance. The upstream barrier wall. elevation is 4,578.0 feet and will protect the ladder from high riverflows. If the ladder was open at the upstream end, the ladder structure would be overtopped by water and not functional for fish passage. d. For flows above 8,000 cfs to 28,000 cfs, the spillway will carry the majority of the riverflow with approximately 1 foot of freeboard- all-owed at the maximum flow. The ladder itself will be over- topped, also passing a portion of the floodflow. e. For the standard operational conditions, auxiliary water must be added at the junction pool diffusers to maintain normal • 12