Earlier this week, the Grant PUD declared a non-failure emergency at Priest Rapids Dam. The announcement came after inspections revealed leaking in spillway monoliths. Grant PUD will reduce reservoir elevation behind the dam to normal operating minimums while inspection work continues. Priest Rapids Dam will continue to generate electricity. Dam operations will continue as usual.
There is no threat to life or property. The Priest Rapids Reservoir will be held to operating elevations between 484.5 to 481.5 feet above sea level. This is within the lower end of the normal operating range. The maximum reservoir elevation is 488.0 feet. The leaking in the spillway structure was discovered by a contract crew drilling inspection holes. The reservoir will remain at the lowered level at least until the inspection work is finished.
The issue is different than the one at Wanapum Dam in 2014, when a fracture was found on the spillway. That repair required a prolonged reservoir drawdown. Wanapum Dam has since been completely repaired.
The Priest Rapids spillway monoliths are stable, but merit further investigation. The dam has 22 spillway monoliths. A monolith is the expanse of concrete below each of the dam’s spill gates. Crews will drill inspection holes downward from an internal passageway called “the grout gallery” that runs the length of the spillway. When the drilling is finished, Grant PUD will devise a repair strategy, if necessary, once analysis is complete. The investigation and drilling at Priest Rapids Dam is precautionary work after completing the repair at Wanapum Dam in 2015.
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