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Potential failure situation developing at Wanapum Dam

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The discovery of a crack in a concrete pier at Wanapum Dam has led the Grant County PUD to lower the dam reservoir by 6 feet to relieve pressure.

Correction: The crack at Wanapum Dam is on the dam’s upriver side. That was incorrect in the original version of this story.

BEVERLY — Grant County PUD has alerted emergency officials, state agencies, other dam operators and downstream property owners that a potential failure situation is developing at Wanapum Dam.

PUD spokesman Tom Stredwick said that the “Emergency Action Plan B” was declared at approximately 3 p.m. Friday. That level of alert means that a potential failure situation is developing, he said.

The alert is akin to a “Level 1” wildfire evacuation notice, he said. Under a Level 1, residents who live within the vicinity of a fire are advised to be alert to danger and follow emergency and news broadcasts, but to stay in their homes.

Catastrophic failure is very unlikely,” PUD assistant general manager Chuck Berry said late Friday. “We’re generating now. We’re not anticipating a huge amount of water coming. In a worst-case scenario and that piece of the spillway would fail, the flows that would move into the river below would not exceed the regular flow of the Columbia River. There is plenty of room to handle it.”

PUD General Manager Tony Webb said it’s too soon to tell what caused the crack, but they’re investigating and focused on safety. “We have good people on it,” he said. “We’ve got the right mission — public safety and health and protection of the dam. We’re trying not to get distracted to see how we stabilize it, how to fix it and move on. I want my staff focused.”

The heightened alert at the dam comes after divers Thursday discovered a crack in one of the dam’s concrete support piers that measures 2 inches wide by 65 feet long.

The PUD will draw the reservoir behind the dam down another 14 feet by Tuesday for a total expected drawdown of 20 feet, Stredwick said.

The drawdown is to reduce pressure on the dam and help ensure the vulnerable area remains stable. No further movement has been detected at the pier since the irregularity was detected Tuesday, Stredwick said.

The crack runs horizontally along the upriver face of the spillgate pier, Stredwick said. It’s about 75 feet below the water’s surface. It runs the entire width of the 65-foot-wide pier, which is 126 feet tall and 92 feet from front to back.

PUD officials have not said what could have caused the crack, Stredwick said.

The dam is currently generating enough electricity, along with the PUD’s other powerplants, to cover county demand for electricity, Stredwick said.

If generation is stepped down at the dam, the utility will buy the power it needs on the regional wholesale power market. PUD customers should not see any interruption in service, he said.

Boat ramps on the Columbia River from Wanapum Dam upriver to Rock Island Dam will be unusable after the dam’s reservoir is drawn down by Tuesday, he said.

Federal inspectors were at the dam Thursday.

Wanapum Dam is the PUD’s largest powerplant, capable of generating 1,092 megawatts of electricity, enough to supply nearly 900,000 Northwest homes. It’s just south of Vantage where Interstate 90 crosses the Columbia River.

Engineers were tipped to a possible problem Tuesday when they noticed a slight bowing of a concrete curb on the dam deck. They also noticed that the affected spillgate was misaligned. The irregularity would likely have gone unnoticed by anyone not very familiar with the dam, he said.

Those guys are out there every day and study the dam from every angle,” he said.

Dams have “expansion joints” that let them flex with changes in water pressure and temperature, Stredwick said. But measurements taken at the dam showed that the movement at Wanapum was “outside historical norms.”

Reach Christine Pratt at 509-665-1173 or . Follow her on Twitter at @CPrattWW.