Investigative drilling is currently underway in a bid to discover the cause of a fracture in one of the spillways at Wanapum Dam in Washington, US.

Grant County PUD is working with contractor Kuney-Goebel JV and subcontractors on the precise drilling project at spillway pier monolith No. 4, where the crack was discovered in February.

The project – expected to be complete later this week – is part of an extensive evaluation being conducted on the structure, with data from the examination to be used by a team of Grant PUD engineers, an independent board of consultants, and Federal Energy Regulatory Commission (FERC) officials to determine the best way to repair the structure and possibly raise the elevation of the Wanapum reservoir to an intermediate level during the restoration phase.

No additional damage to the dam was found during a thorough inspection, other than some minor surface damage on spillways neighboring monolith No. 4.

Grant PUD is considering the use of steel strand anchors that are drilled from the top of the dam through the concrete structure into bedrock to repair the spillway, but are awaiting the results of the ongoing evaluation to help determine if this process would be an effective solution.

Along with the forensic evaluation of spillway pier No. 4, fish biologists, engineers, and stakeholders are developing plans to modify the fish ladders at Wanapum Dam. The modifications include installing a pumping system and creating temporary slides at the top of the fish ladders so returning adult salmon and steelhead can safely pass the dam and into the drawn-down reservoir.

While the work is ongoing, Wanapum dam is continuing to generate electricity, but at a reduced rate.

Photo: A slight bend is noticable in the conduit below the guardrail, resulted in the discovery of the crack (Courtesy GrantCounty PUD)