Canyon Ferry Dam and Powerplant are on the Missouri River about 1.5 miles downstream from the original Canyon Ferry Dam and the Montana Power Company's 6,700 kilowatt in the backwater Hauser Lake. The dam is a concrete gravity structure approximately 1,000 feet in length along the crest with a structural height of 225 feet. It contains 414,400 cubic yards of concrete. The spillway is an overflow section in the central portion of the dam, controlled by four radial gates. The spillway capacity is 150,000 cfs. The total capacity is 2,051,000 acre-feet at elevation 3,800.00. Four river outlets are in the spillway section of the dam. The maximum discharge capacity of these outlets is 9,500 cfs. One 156-inch-diameter pumping intake pipe is embedded in the concrete of the dam near the left abutment for the Helena Valley Pumping Plant. Three 162-inch-diameter penstock pipes for the power generating units are embedded in the dam near the right abutment. The powerplant is on the right downstream toe of the dam adjacent to the spillway apron. It is of reinforced concrete construction and houses three 16,667-kilowatt vertical-shaft generators driven by 23,500-horsepower turbines.
Foundation Geology:Massive, fine-grained, hard and dense hornfels (transformed empire shale) fractured into an exceedingly complex and closely spaced system of joints, with several minor and one major fault zone and a major bedding plane slip. Special treatment: Grout blanket over foundation area and grout curtain under dam.