YAKIMA, Wash. (AP) Supporters of the proposed Black Rock Reservoir near Yakima are admitting they made a $2 billion error in estimating how much money would come from electricity produced by the project.

But they also contend the error doesn’t doom a project they believe is the answer to solving a variety of water problems in the Yakima River Basin.

The Yakima Basin Storage Alliance had released a recent report contending that power sales, benefits to irrigators and improved fish runs in the Yakima River ultimately will outweigh the reservoir’s $4.2 billion cost.

Charlie de la Chapelle, a Yakima Valley fruit grower who is vice chairman of the alliance, said the grass-roots group regreted the mistake.

“We apologize for the error. We vow to scrutinize numbers we release more carefully, and stand behind our other public statements,” de la Chapelle said.

The alliance includes business and agriculture interests that favor Black Rock, a proposed 1.3 million acre-ft. reservoir in the Black Rock Valley, 30 mi, east of Yakima. The reservoir would draw water from the pool behind Priest Rapids Dam.

An acre-ft. is the amount of water that would cover one acre a foot deep.

The stored water would serve Yakima Valley irrigators under current plans. It also would leave more water in the Yakima River to improve habitat for migratory and resident fish, supporters said. Two fish species in the Yakima River, Steelhead trout and Bull trout, are listed as threatened under the Endangered Species Act.

The revised estimate for revenue from power generation, issued by the alliance Jan. 11, is now $412 million over a 40-year period, which alliance officials said is a period generally accepted in the power industry.

Their initial report, prepared by a Portland, Ore., consulting firm, had estimated the power benefits at $2.4 billion. But that was based on an error in which the consultant mistook the estimated lifetime power revenues for annual revenues and multiplied them.

Correcting the error reduced the current projected Black Rock benefits to $3.8 billion, an amount that is less than the estimated construction cost of $4.2 billion.

But the alliance said additional benefits would include approximately $2 billion for the value of land in residential and resort development that would surround the reservoir, and $1.28 billion from spending for tourism and recreation.

The alliance, with financial support from Benton and Yakima counties and the Port of Sunnyside, launched the studies 18 months ago.

The U.S. Bureau of Reclamation in November concluded the reservoir would return only 30 cents on the dollar if it was built.

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