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Wanapum Dam Spillway

Quick, collaborative action averts spillway crisis

Vantage, Washington

In late February 2014, a crack was discovered at the Wanapum Dam Spillway. The project owner, Grant County Public Utility District, immediately consulted with the Federal Energy Regulatory Commission (FERC), lowered the reservoir, and sought out help.

By drilling through the spillway, the team determined the extent and orientation of the crack. The solution? Post-Tensioned Anchors (PTAs) to repair the cracked monolith and mitigate the potential for further cracks. However, the drilling needed to be extremely precise to avoid hitting critical features.

To return the dam to working order as quickly and safely as possible, the first remedial action was to drill vertical drains that provided pressure relief for the lift joints. More than 100 lift-joint drains were installed in the spillway monoliths and then the PTA installation was sequenced to allow an intermediate pool raise, returning the fish ladders to normal operations. All while protecting culturally sensitive sites along the reservoir shoreline.

Through cooperation between the District, our team, construction contractors, and regulators, operations were back in full swing in March 2015, just over a year after discovery of the crack.

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