Arrowrock Dam Gains New Lease On Life: Three-Year Construction Project Finished

Media Contact: John Redding, (208) 378-5212
Jerrold Gregg, (208) 383-2248

For Release: September 10, 2004

Three years of construction are now completed at Arrowrock Dam, giving a new lease on life to the historic 1915 structure located on the main stem of the Boise River about 20 miles east of Boise, Idaho.

Construction crews supervised by the Bureau of Reclamation worked continuously at Arrowrock Dam to install 10 new clamshell gates that replaced the 89-year-old Ensign valves that have been in continuous operation since the dam was first constructed.

"Installing these new gates required holding the reservoir behind the dam at record low levels in order to ensure the safety of the work crews, but the end result is a much safer and more efficient method to regulate the flows along the Boise River," said Jerrold Gregg, Reclamation Snake River Area Office manager. The new outlet works will provide flood control benefits to the Treasure Valley.

Reclamation worked closely with irrigators, fishery biologists, recreation interests, and the U.S. Army Corps of Engineers to manage flows during construction in order to ensure adequate water for all interests.

"This was a major project on the Boise River that called for public input and cooperation from many groups in the Treasure Valley. I think we can be proud of this effort and of the final result," said Gregg.

Cost for the project was about $20 million and required both Congressional funding and local cooperation with the irrigation districts that will benefit from the continued efficient delivery of water. The new clamshell gates are located on the downstream side of the dam, making it safer for maintenance and inspection to take place without dewatering the reservoir.

Special attention was also given to bull trout, a species presently listed as threatened. Fisheries biologists with Reclamation, the Idaho Department of Fish and Game, US Fish and Wildlife Service, and US Forest Service have worked closely to monitor the health of the fish throughout the construction process. "Reclamation also completed four years of engineering studies, National Environmental Policy Act compliance, and extensive planning and public meetings prior to construction," said Gregg. Arrowrock Dam is part of Reclamation's Boise Project



A power plant at the Boise Diversion Dam, consisting of three 500-kilowatt units, was built in 1912 to furnish electric power for Arrowrock construction crews.

A sawmill and sand cement plant was built at the site to provide all the lumber and cement needed for the construction work.

The dam is a 350 foot high, 1,150 feet long concrete thick-arch structure with a overflow spillway with 6 large drumgates, 20 ensign valves, and 5 sluice gates.

At the time of construction, Arrowrock Dam was the highest dam in the world.

A seventeen mile standard gage railroad was built to connect Arrowrock City (the construction camp) with Barber Junction just northeast of Boise. This was for the transport of men supplies and building materials.

Excavation for the foundation began in 1913 with work completed on the dam in September of 1915, with construction costing $4.8 million.

Dedication ceremonies took place on October 4th and 5th of 1915.

Construction materials used were:

610,000 cubic yards of concrete

1,950,000 pounds of steel

More than 6,000,000 board feet of lumber

On the National Historic Register in 1976



WHEN: FRIDAY, SEPTEMBER 17, 2004 - 11:00 a.m.





WHO: Very brief opening remarks: Bureau of Reclamation Commissioner John Keys; Vernon Case, Director of the Wilder Irrigation District; Jerrold Gregg, Manager of Snake River Area Office; Congressional Representation: Senator Craig's office: Mike Freese; Senator Crapo's office: Layne Bangerter; Congressman Simpson's office: Nikki Watts; Congressman Otter's office: Josh Tewalt

VISUALS: A Ceremonial 'Countdown' will include pressing a button and rushing water from the downstream side of the dam through all ten of the new valves. (Impressive visual)

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Reclamation is the largest wholesale water supplier and the second largest producer of hydroelectric power in the United States, with operations and facilities in the 17 Western States. Its facilities also provide substantial flood control, recreation, and fish and wildlife benefits. Visit our website at and follow us on Twitter @USBR.