Work continuing on Wanapum Dam spillway

26 June 2014

Wanapum Dam: a drill rig bores out a hole for an anchor tendon that will go from the top of the spillway into bedrock below the dam.

Grant County PUD has said work is continuing around the clock on the 800ft (243.8m) long Wanapum Dam spillway in Washington State, US, to prepare for final reinforcing repairs, with plans to increase river elevation by the end of the year.

Various types of drilling is underway as crews prepare for repairs once they are approved by the Federal Energy Regulatory Commission (FERC). Holes are being drilled throughout the spillway in anticipation of high strength cables (tendons) being installed from the top of the dam into the bedrock below. Repairs will also likely include additional reinforcing anchor bars in the upstream and downstream sides of the spillway.

All repairs are to occur over the summer allowing the utility to increase the river elevation in the fourth quarter of 2014. Costs are still on track at the $61 million estimate, the PUD said.

Wanapum Dam remains stable and is operating at approximately 50% capacity.

The river elevation above the dam has been reduced by approximately 25ft (7.6m) while repairs occur.

A fracture was detected in the dam¹s Wanapum dam's spillway pier monolith No. 4 by divers on February 27, three days after a worker noticed that the top of the spillway pier had shifted slightly downstream.

Grant County PUD has said that a mathematical error during the pre-construction design of the dam may be partly to blame for the fracture developing.


Image: A drill rig bores out a hole for an anchor tendon that will go from the top of the spillway into bedrock below the dam. Each of the 13 spillway monoliths will be reinforced with anchor tendons.



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