Concern at PUD over crack in Wanapum Dam found in spillway structure

BEVERLY - They are saying there is no immediate danger of major flooding, but officials at Grant PUD are concerned about a crack discovered last Thursday, Feb. 27, in a spillway structure at Wanapum Dam.

All portions of the dam are monitored 24-7 daily, PUD Public Information Officer Chuck Allen said. However, this spillway is now under greater watch.

"These dams are built to withstand things like this," he said.

Still, the PUD will proceed cautiously. It is draining the Wanapum pool about 20 feet to take pressure off the spillway and allow inspection divers to work.

"We've closed all the boat launches in the Wanapum and Priest Rapids pools. You can't access the river anyway," Allen said.

Allen said all of the other dams on the Columbia have been alerted. There is a plan for coordinated flow management if it is needed.

Allen said the drawdown will diminish the PUD's power production. He said the PUD is already buying power on the wholesale market to make up the difference.

According to Allen, the reason for the crack has not been discovered. He said there is no timetable for a resolution.

Suspicion of a problem at one of 12 spillways arose on Monday, Feb. 24, when a worker noticed a mis-alignment in the roadway that crosses the Columbia River atop the dam.

"It's supposed to be straight," Allen said.

Alerted Officials observed the same mis-alignment, concluded that something was wrong and called for action. On the 27th, divers discovered structural damage on one of the spillways.

Survey readings taken earlier in the week showed that the area has moved outside of historical norms. According to Allen, a monolith at the affected spillway has moved "a few inches," and "more than it should."

Allen said the crack runs across the entire 65-foot width of the spillway. He said the crack is up two inches wide in places.

According to Thomas Stredwick, another PIO, alignment surveys taken late in the week did not show additional movement of the spillway section.

Working in conjunction with the Federal Energy Regulatory Commission and independent engineers, Grant PUD continues to inspect, he said.

By Monday, March 3, water levels above Wanapum Dam (forebay) were anticipated to be 20 feet lower than the normal high operating level.

A spillway is the portion of the dam that allows water to "spill" past the dam as opposed to running through the turbines. The spillway consists of multiple, independent structural sections that support the spillway gates.

Each of Wanapum Dam's 12 spillway gates are capable of passing roughly 80,000 cubic feet of water per second based on current river conditions. In a worst case scenario, Stredwick said, if one of the spillway sections fails, the remainder of the spillways and the main dam structure would remain intact.

"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," Stredwick said.

The team of engineers and regulatory agency personnel worked through the weekend to provide constant monitoring and on-going evaluation of the area.

"Public safety is the utility's paramount concern," Stredwick said.