Arrowrock Dam

Repairs to three Arrowrock Dam gates took three days.

Repairs to three malfunctioning gates on the downstream side of Arrowrock Dam limited the loss of water, a manager says.

An estimated 7,100 acre-feet of water was lost in the Boise River system in September as the U.S. Bureau of Reclamation completed repairs to the clamshell-like gates, said Bryan Horsburgh, deputy area manager for the bureau’s Snake River Area Office in Boise.

Crews repaired one on Sept. 20 and the other two Sept. 22.

“The gates are running correctly and we have returned to normal fall operations,” Horsburgh said Oct. 4.

The Reclamation-owned dam is in the middle of the three-dam Boise system. The bureau also owns Anderson Ranch Dam upstream. The U.S. Army Corps of Engineers owns Lucky Peak Dam downstream. Water stored in the reservoirs is important for irrigation and other uses across the region.

Arrowrock Dam’s downstream wall marks the upstream end of Lucky Peak Reservoir, which the Corps says has a total storage capacity of 306,000 acre-feet.

Horsburgh said Reclamation and the Corps cooperated on necessary outflows from Lucky Peak.

At Arrowrock, “normally we would have closed the gates when irrigation demand decreased,” he said. “This year we had to leave them open until the Lucky Peak pool dropped enough to access the gates.”

Water flows through Arrowrock Dam via a penstock on the upstream side and clamshell gates, which are parallel to each other, on the downstream face.

Reclamation discovered the gates were stuck partly open during spring and summer operations, when water in the Lucky Peak Pool was too high to accommodate repair access.

“Every drop of water is important,” Horsburgh said. “Reclamation is pleased that we were able to repair the gates as soon as possible.”

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