Evaluations continue at Grant PUD’s Wanapum Dam

The Grant County Public Utilities District will work with contractor Kuney-Goebel JV and subcontractors to begin investigative drilling after a crack was discovered in Wanapum Dam’s pier monolith No. 4 in February.

HydroWorld.com previously reported that divers found a 65-foot-long by 2-inch-wide horizontal crack after a worked noticed a slight bend in a conduit that runs the length of the dam, indicating a potential shift in Wanapum’s structure.

The discovery led Grant PUD to begin a drawdown of waters upstream of the structure, lowering their levels by more than 25 feet.

Now, the utility said, it will conduct an “extensive evaluation on the structure to help determine the cause of the fracture and its geometry”, including a drilling project that is expected to take nine days.

Data from the study will be used by Grant PUD engineers, an independent board of consultants and Federal Energy Regulatory Commission (FERC) officials to determine the best way to repair Wanapum and possibly raise the reservoir’s elevation during the restoration.

“To repair spillway pier No. 4, Grant PUD is exploring the possibility of using steel strand anchors that are drilled from the top of the dam through the concrete structure into bedrock,” the utility said in a release. “The steel strand anchors would be set into place with a specialized, high-strength grout.”

Grant PUD is also working with biologists, engineers and other stakeholders to develop a fish ladder modification plan. The changes are necessitated by the drawdown, Grant PUD said, and will include a pumping system and temporary slides to allow for returning adult salmon and steelhead to pass the dam into the reservoir.

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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Michael Harris formerly was Editor for HydroWorld.com.

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