YAKIMA — The cracked Wanapum Dam should be repaired and its reservoir on the Columbia River near Vantage refilled by the end of the year, the Grant County Public Utility District said.
Workers for the utility have started drilling holes that will be used to anchor the dam in bedrock.
“It’s almost like putting a screw down into a block of wood,” said spokesman Thomas Stredwick.
The final repair plan is awaiting approval from the Federal Energy Regulatory Commission but drilling anchor holes in advance will save time, the Yakima Herald-Republic reported Wednesday (http://bit.ly/1iFdEF3 ).
After the 65-foot-long spillway crack was discovered in late February, the utility lowered the reservoir 26 feet to reduce pressure. That left boat ramps and fish ladders high and dry. All shore access behind the dam was closed for public safety and to protect archaeological sites.
The utility modified fish ladders, and more than 23,000 spring chinook have passed the dam successfully, Stredwick said.
In May, the utility determined the crack was caused by a math error during the dam’s original construction in the early 1960s. More concrete and reinforced steel should have been initially used in all 13 of the spillway’s supporting blocks.
Workers are drilling three holes through each concrete block for steel cables that will be secured into the bedrock, then tightened to close the crack.
The repair work is expected to cost about $61 million, Stredwick said.
By late fall, the utility plans to begin raising the reservoir level slowly, to make sure the repaired dam remains stable. Bringing the water up 19 feet should be enough to restore public access to boat launches and recreational areas.