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65-Foot Crack Found in WA Dam

Tuesday, March 4, 2014

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Federal, county and independent engineers have teamed up on an emergency response to safeguard the Wanapum Dam in Washington State after divers discovered a two-inch-wide, 65-foot-long crack in a spillway pier.

Water levels in the Wanapum Reservoir on the Columbia River were drawn down 20 feet by Monday (March 3) to reduce pressure on the spillway, officials said.

Wanapum Dam
Photos: Grant County PUD

A spokesman called the problem serious but said it "posed no immediate threat."

The level was reduced six feet last week and an additional 14 week over the weekend.

'Serious' But 'No Immediate Threat'

A team of engineers and Federal Energy Regulatory Commission personnel has been constantly monitoring and evaluating the structure, and officials have warned downstream towns and government agencies about the damage.

All boat launches on the Wanapum Reservoir and the Priest Rapids Reservoirs downstream have been closed.

“At this point, we already know there’s a serious problem,” Grant County Public Utility District spokesman Thomas Stredwick told reporters last week. However, he added, "there's no immediate threat to public safety."

'Bowing' Seen

Divers discovered the structural damage Thursday (Feb. 27) along the base of one of the spillway piers after an engineer noticed a “bowing” in the roadway above the dam, Stredwick said.

Inspectors later discovered that the 820-foot-long spillway was raised 2.5 inches above the water.

Wanapum Dam

The crack in a spillway pier was found after an engineer noticed “bowing” in the roadway above the dam. Later readings found movement in the structure.

"Survey readings taken earlier this week showed that the area has moved outside of historical norms," Stredwick said in a statement Thursday.

Subsequent readings showed no additional movement, he added.

The drawdrawn was ordered "to reduce the pressure on the spillway while inspectors investigate," Stredwick said.

Spillway Set-up

Spillways allow the water to “spill” past the dam, rather than running through the turbines. The spillway consists of multiple, independent structural sections that support the spillway gates.

Each of Wanapum Dam’s 12 50-by-68-foot spillway gates is capable of passing roughly 80,000 cubic feet of water per second based on current river conditions, the utility said.

Wanapum Dam

The Wanapum Dam stretches more than a mile across the Columbia River, just downstream from I-90.

"In a worst-case scenario, if one of the spillway sections failed, the remainder of the spillways and the main dam structure would remain intact," the utility said. "Under current conditions, the amount of water that would flow through this section of the dam would be within the range of normal river conditions."

The dam is still generating electricity for 45,000 customers. No repair plan or cost estimate has been released.

About the Dam

Named for a Native American tribe that lives along a stretch of the Columbia River, Wanapum Dam is located six miles downstream from Vantage, WA; 18 miles upstream of Priest Rapids Dam; and 415 miles above the mouth of the river. It is just downstream from where Interstate 90 crosses the river.

The $93.2 million structure opened in July 1963 after four years of construction. Wanapum Dam was financed by long-term revenue bonds that were retired through the sale of power.

The dam is 8,320 feet long and 185 feet high from its deepest excavation point.


Tagged categories: Concrete; Cracks; Infrastructure; Locks and dams; Rehabilitation/Repair

Comment from Terry Wunderlich, (3/4/2014, 4:04 AM)

What about the Hanford Site and runoff into the Columbia River?

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