Infrastructure protectionNew earthquake assessment finds increased risk for Washington Dams

Central Washington state has always been considered low risk for earthquakes back when big hydropower dams went up on the Columbia River many decades ago. A recently completed seismic hazard assessment, however, shows that there is a much greater earthquake potential for the area than previously thought.

Now, dam owners have to figure out whether their dams can hold up to an earthquake. If retrofits are needed, they could cost hundreds of millions of dollars.

If you follow the curves of the Columbia River downriver through central Washington, you will pass by Wells Dam, Lake Chelan Dam, Rocky Reach, Rock Island, Wanupum, and Priest Rapids Dam.

When these dams were built no one considered this part of the state susceptible to earthquake.

“The potential always existed. You know, we’re just more aware of it and we have a better understanding now of what the potential loads are,” Grant County PUD Hydro Engineering manager Kevin Marshall told Oregon Public Broadcasting (OPB).

This “understanding” comes from a newly released seismic hazard reassessment of the Mid-Columbia region. The assessment took four years to produce and was commissioned by three Central Washington public utility districts.

“Our Chelan and Rock Island structures were designed and built in the 1920’s and early 30’s,” says Bill Christman, Marshall’s counterpart at Chelan County Public Utility District (PUD). “Back then, people didn’t have a good understanding of the earthquake potential. And if there was an earthquake, they didn’t consider it to be catastrophic necessarily, because the region was virtually unoccupied.”

The area is now heavily populated and the estimate of how strongly the ground could shake has tripled or quadrupled. Seismologist Ivan Wong thinks the risk comes from the crumpling of the Earth’s crust roughly between the Oregon-Washington borders.

“Those folds, those geologic structures we see in the Yakima Fold Belt are underlain by faults that can rupture in large magnitude earthquakes,” Wong told OPB. “Probably in the range of the upper magnitude sixes to maybe more than magnitude seven.”

Now people are wondering whether the dams will survive an actual earthquake.

“They will survive, but there will be some triage necessary,” Christman told OPB. “They won’t survive without some damage. We don’t think there will be any uncontrolled rapid release of water, which is one of the standards we use to try to decide what if anything do we need to do before an earthquake to really protect those structures.”

According to Brian Becker the dam safety chief for the Federal Bureau of Reclamation, large dams like the ones in Japan can survive almost anything.

“In Japan, there was a report of one failure and I think seven dams that were damaged,” Becker told OPB. “In general, I think the dams fared relatively well. So maybe there’s some comfort and solace in that.”

The Mid-Columbia dam owners and their federal regulator are leaving nothing to chance as they have said they are prepared to spend as much money as it takes to protect against an event that happens once every 10,000 years.

Grant and Chelan County PUD started to analyze specific vulnerabilities at each of their dams even before the ink was dry on the regional seismic study. The next round of studies promise to open a tough debate about what price for what degree of safety.

“When you get into dam issues where you have to do remediation, it gets very expensive very quick,” Marshall told OPB.

“A good example I think is we’ve got these big transformers on the deck of the dams that could fall over or be misplaced,” Christman said. “Just tying things down and responding in a way that keeps things from falling over in a big ground shaking event costs a lot of money.”

The multimillion dollar cost for the retrofits will come out of ratepayer pockets. The three Mid-Columbia public utility districts sell surplus power throughout the Northwest, so pretty much the entire state could be chipping in at some point.