Discharge Facilities at Hells Canyon Dam

Design of Hells Canyon Dam on the Snake River for the Idaho Power Company required careful consideration to arrangement in fitting the diversion, power and spillway facilities within the deep narrow gorge. Each feature arrangement is described. Hells Canyon Dam is a straight concrete gravity structure. The diversion tunnel is concrete lined and has a 40-ft diam horseshoe section, 1700 ft long to handle 60,000 cfs. The three-unit power plant with 391,500 KW nameplate capacity is notched into left abutment rock and overlaps the toe of the dam. Energy of 300,000 cfs discharge over the center section spillway is dissipated by a combination of concrete nappe deflectors and a submerged roller bucket. Fish trapping facilities adaptable to the 48-ft tailwater fluctuation consist of an aluminum barge floating in the tailrace.