Under the Black Rock proposal, the Bureau of Reclamation would divert water from the Columbia River, out of the reservoir behind Priest Rapids dam, and pump it several miles uphill (1400 foot elevation gain).  The Black Rock reservoir would contain 1.3 million acre-feet of water (423 billion gallons), and when full, would have a surface area of 3.25 square miles.  The reservoir would be perched east of the City of Yakima, but face eastward, toward the U.S. Department of Energy’s Hanford facilities. 

The dam would be very large at approximately 6,000 feet long and 760 feet high.  For example, Grand Coulee Dam (below) is 5,223 feet long and 550 feet tall.  However, Lake Roosevelt reservoir, behind Grand Coulee, holds nearly 100 times more water than would Black Rock.  (For more Grand Coulee Dam statistics, click here.)

Grand Coulee Dam is smaller than the proposed Black Rock Dam.  Photo: U.S. Bureau Reclamation

The Black Rock proposal is styled a “water exchange.”  That is, Black Rock water would substitute for some of the water that the Bureau of Reclamation currently diverts from the Yakima River and delivers to irrigation districts in the lower Yakima Valley.  This would allow some Yakima River diversions to cease, ostensibly improving instream flows in the Yakima River for the benefit of salmon and other fisheries and water quality. 

Improvements for fish are cited as significant public benefits of the Black Rock proposal.  Public benefits can be used as a basis to transfer the cost of building water supply dams from irrigators to the public.  However, even with the improvements to Yakima River fisheries, the cost-benefit analysis for Black Rock shows it to be a losing proposition.

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