EPHRATA — Operators at Wanapum Dam say they expect to have repaired enough of a 65-foot crack to restore the river to nearly normal levels by year’s end.
When the crack was discovered in the dam’s spillway in late February, the Grant County Public Utility District (PUD) drew water levels behind the Columbia River dam down 26 feet to reduce pressure on the fractured area. The move stabilized the dam, but left boat ramps and fish ladders high and dry. All public access to the river behind the dam has been closed for safety and to protect archaeological sites.
In May, the PUD determined that 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. The PUD now plans to strengthen the entire spillway, spokesman Thomas Stredwick said.
Workers are drilling three holes through each concrete block so that steel cables can be installed. The cables will be secured into the bedrock, then tightened from the top to close up the crack and increase the blocks’ ability to withstand the water pressure by compressing them.
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Details about the steel cables are waiting for approval from the Federal Energy Regulatory Commission, but the PUD is drilling the holes in advance to save time, Stredwick said.
“Once the plans have been approved, the installation of the actual tendons can go pretty quickly,” he said. “The drilling part is the slowest process.”
In late fall, the PUD plans to begin raising the reservoir level slowly, to make sure the repaired dam remains stable, Stredwick said. Bringing the water up 19 feet should be enough to restore public access to boat launches and recreational areas.