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Boise River Diversion Dam
Boise River Diversion Dam is located in Idaho
Boise River Diversion Dam
Location of Boise River Diversion Dam in Idaho
Country United States
Location Ada County, Idaho
Coordinates 43°32′15″N 116°05′36″W / 43.53750°N 116.09333°W / 43.53750; -116.09333
Status Operational
Construction began 1906
Opening date 1909
Owner(s) USBR
Dam and spillways
Impounds Boise River
Height 68 ft (21 m)
Length 500 ft (152 m)
Elevation at crest 2,829 ft (862 m)
Width (crest) 12 ft (4 m)
Width (base) 100 ft (30 m)
Spillway capacity 37,700 cu ft/s (1,068 m3/s)
Creates 1,200 acre⋅ft (1,480,178 m3)
Power station
Commission date 1912
Turbines 3 x Francis turbines
Installed capacity 3.45 MW

The Boise River Diversion Dam is a diversion dam on the Boise River in the U.S. state of Idaho, 7 miles (11 km) southeast and upstream of Boise in Ada County. Completed in 1909, it is operated by the U.S. Bureau of Reclamation. The diverted water fills the concrete New York Canal, the primary irrigation channel for Ada and Canyon counties.


In March 1906, the Utah Fire Proofing Company began work on the Boise River Diversion Dam with the provision that the structure would be completed within one year. It soon became apparent that the dam would not be finished on time. With little experience in such endeavors, Utah Fire Proofing failed to provide adequate foremen for the project. At least nineteen superintendents worked on the dam and their incompetence led to an extraordinary turnover in labor. Inclement weather and flooding caused at least two months' worth of delays and forced the crews to rebuild part of the structure. By April 16, 1907, the dam was only 41% complete. It would take another year and a half before the diversion works were ready to unload into the New York Canal. The company eventually lost $90,000 on the contract. And to make matters worse in March 1909, a log foreman "maliciously" removed the boom above the dam and allowed timber roll over the embankment causing $73,000 worth of damage. Yet when the structure was completed it worked famously. The Diversion Dam is 68 feet (21 m) high and 500 feet (152 m) in length with an overall capacity of 42,815 cubic feet per second (1,212 m3/s).


To provide power for the construction of Arrowrock Dam upstream, Reclamation retrofitted the Diversion Dam with a small powerhouse. Finished in 1912, the plant's three generators produced 1,500 kilowatts of electricity for Arrowrock's camp, sawmills, and giant cement mixers. The Allis-Chalmers 725 horsepower (541 kW) turbines were the first in the world to be built with a vertical shaft design. Along with the power lines, government forces hung a two way phone cable to connect Arrowrock with the outside world. In 1976, the power plant was added to the National Register of Historic Places. After being refurbished by the Bonneville Power Administration in 2002, it is now on ready reserve status and occasionally provides surplus power during times of peak demand. Special care was made to maintain the historic qualities of the powerhouse. The original governors, slate control panels, transformers, overhead crane, and generator housings, although no longer functional, were retained for historic purposes.

View from upstream
  • Historic American Engineering Record (HAER) No. ID-17-A, "Boise Project, Boise River Diversion Dam, Across Boise River, Boise vicinity, Ada County, ID"
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