LEWISTON - Upriver from the LC Valley is Dworshak Dam. Army Corps of Engineers officials say a new rating system has led to a better way of sharing with the public some concerns about Dworshak that need to be addressed.
Donna Street is Chief of the Engineering and Construction Division at the Walla Walla office of the Corps
Street said Thursday her office has been releasing new information about a nationwide assessment underway by the Corps. That process involves rating the nation's dams on a scale of 1 to 5, based on structural and other considerations, as well as the consequences of a dam failure. It’s called a Dam Safety Action Classification (DSAC).
Dworshak earned a DSAC score of 2.
Street says that is primarily because of the threat to human safety and the economic consequences of a failure. She was quick to point out that there is no indication that a failure is probable in the near or even distant future.
While the Corps says the probability of failure is relatively low, they do acknowledge that there are some concerns about seepage and leakage through the dam's foundation and joint drains. This causes what is called uplift pressure, and could lead to cracks in the dam’s monoliths.
Street said inspections show that there are no cracks in the dam. And she added that the new rating process is meant to help prioritize funding for further monitoring, planning and mitigation of problems at Dworshak and other dams.
Street said the Corps has finished inspecting about 30 percent of the nations 610 dams, first looking at those that pose the greatest risk. She said the remainder of the dams will undergo the rating process over the next two fiscal years.
Street said Dworshak is monitored on an ongoing basis, and inspections are conducted every month by staff at the dam. Annually engineers from the district office in Walla Walla inspect the dam. And every five years there is a “formal” inspection with senior Corps engineers and engineers from other agencies.
The last formal inspection was conducted in June of 2007.
The Corps says, in the unlikely event of a failure at Dworshak, the impact would be “very high” and would extend all the way to McNary Dam.
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