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Anderson Ranch Dam

Anderson Ranch Dam
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Boise Project
Anderson Ranch Powerplant
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Anderson Ranch Dam and Powerplant is a multiple purpose structure that provides benefits of irrigation, power, and flood and silt control. The dam is 456 feet high and is on the South Fork of the Boise River, 28 miles northeast of Mountain Home. It has a total storage capacity of 474,900 acre-feet (active 413,100 acre-feet) and was the world's highest earthfill dam at the time of its completion in 1950. The power plant had a rated capacity of 27,000 kilowatts with two units installed. These units were up-rated in 1986, increasing the capacity to 20,000 kilowatts each for a total of 40,000 kilowatts.


Anderson Ranch Dam is located near the southwestern edge of Idaho Batholith which is composed of a series of closely related, coarse-grained intrusions. Major normal faulting in the region includes faults in and adjacent to the Batholith, faults bounding the northeast and southwest margin on the adjacent Snake River Plain, and faults forming Camas Prairie Basin east of the dam. These faults show a low to moderate seismic activity level. The dam is located in a narrow steep-sided valley cut through several hundred of igneous extrusive and extrusive rock. In the dam foundation, the rock was found to be intensely fractured and cut by numerous shears and fractures of varying widths. Several dikes were also found normal to the canyon axis. The dikes present a reduction of fractures and shears reducing the foundation permeability and making a tight foundation. Materials within the canyon include talus, colluvium, alluvium, residual soil and intact rock. These materials form the foundation of the dam and have performed well with respect to deformation and seepage.

Last updated: Nov 21, 2012