Contractors are working around the clock in preparation for final reinforcing repairs of a cracked Wanapum Dam spillway, operator Grant County Public Utilities District said.
“Various types of drilling” are already under way as Grant PUD awaits approval for further repairs from the Federal Energy Regulatory Commission, which will include the installation of high-strength cables being installed from the top of the dam into bedrock below. The repairs will also likely include additional reinforcing anchor bars in the upstream and downstream sides of the spillway, Grant PUD said.
All of the repairs in the US$61 million project are scheduled to take place over the summer, allowing Grant PUD to restore the rivers elevation during the fourth quarter of this year.
The company also said fish passage modifications to both of Wanapum Dam’s ladders have “proven effective”, with more than 23,500 adult Chinook having migrated upstream successfully. Spiral flumes have also been added to existing fish ladders in anticipation of record-breaking sockeye, and summer and fall Chinook runs.
A 38-mile stretch of shoreline from above Wanapum Dam to below Rock Island Dam will remain closed as a public safety precaution and to protect culturally-sensitive sites, Grant PUD said, until repairs at Wanapum are in place.
“While there may be some portions of the shoreline that appear safe, the velocity of water moving through the narrow river channel, and sandy banks creates hazardous conditions for the public,” Grant PUD said in a release. “Recreation sites below Wanapum Dam continue to provide recreation opportunities throughout the summer months.”
Grant PUD released a preliminary report on the Wanapum Dam fracture in May, which said a 65-foot-long by 2-inch-wide horizontal crack in the structure’s pier monolith No. 4 was caused by a mathematical error in the dam’s original design calculations.
The discovery led Grant PUD to begin a drawdown of waters upstream of the structure, lowering their levels by more than 25 feet.
The dam is also home to a 1,038-MW Wanapum hydroelectric plant. Grant PUD the plant is only producing about half the electricity it would under normal river conditions.
The facility is a sister plant to the Priest Rapids project. Combined, the two have an output capacity of nearly 2,000 MW.
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