Investigation of cracked Wanapum Dam monolith pier continues

Wanapum Dam Drilling

A team has completed drilling six investigative holes into Wanapum Dam's spillway pier monolith No. 4 as the Grant County Public Utilities District continues its examining a fracture found earlier this year. reported Grant PUD divers discovered a 65-foot-long by 2-inch-wide horizontal crack in the pier monolith in February, leading the company to hire Kuney-Goebel JV and subcontractors to perform the drilling as part of a forensic investigation in March.

Further drilling will help determine the geometry of the fracture and how far it reaches into the monolith.

The operation will resume after a larger platform is constructed on the monolith to support workers and their equipment, though windy weather has delayed the process. All work on the platform must be done by boat or crane, with operations being stopped when winds meet or exceed 35 miles per hour.

Grant PUD said the platform construction and drilling is expected to take between three and four weeks without wind delays.

The utility is also working on modifications to Wanapum Dam's fish ladders that were necessitated following a drawdown of the reservoir. Pumps are currently being installed in the dam's two fish ladders, and workers are installing weirs and flumes to help migrating fish navigate over the ladders into the reservoir behind the dam.

Completion of the fish ladder modifications is expected to coincide with the start of the spring Chinook salmon run later this month, the utility said, though Grant PUD will initially trap fish at Priest Rapids Dam and haul them in trucks to above Wanapum or Rock Island Dam at the request of agencies and stakeholders. The process will allow the effectiveness of the Wanapum fish ladder modifications to be evaluated.

The dam is also home to a 1,038-MW Wanapum hydroelectric plant. Grant PUD previously said 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.

For more dam safety news, visit here.

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