Dworshak Dam, North Fork Clearwater River, Idaho. Hydraulic Model Investigation

Dworshak Dam, located on the North Fork of the Clearwater River near Orofino, Idaho, is the highest straight-axis concrete gravity dam in the United States 717 feet from foundation to 3,300-foot-long crest. The project includes a powerhouse for six Francis-type units ultimate installation, a selective withdrawal structure upstream from the powerhouse intakes, two spillway bays and three regulating conduits that discharge into a stilling basin, an excavated exit channel, and facilities for migratory fish. The Dworshak National Fish Hatchery was constructed to replace spawning and rearing areas for steelhead trout that formerly migrated into the North Fork. The report describes studies accomplished in four hydraulic models and three full-scale test facilities. Tests and data obtained during development of design of the spillway, regulating conduits, and stilling basin are presented in the report. The design of the skewed regulating conduit entrances were of primary concern in the project. Prototype operation of the outlets resulted in cavitation damage downstream from the valves an aeration deflector was designed in the model to remedy the problem.