Murray lines up $44M for further Hanson Dam repairs

The U.S. Army Corps of Engineers appears likely to receive $44 million for more repairs to the Howard Hanson Dam, which officials hope will prevent major flooding in the Green River Valley at least for a few years.

U.S. Sen. Patty Murray persuaded her colleagues on the Senate Appropriations Committee Thursday to put the money into a supplemental spending bill the Senate is expected to vote on this month.

That money would be used to deepen and more than double the length of an underground curtain of grout designed to temporarily prevent water from seeping through an abutment and weakening the earthen dam.

"That would temporarily put us back to being where the dam was before it was damaged," said Corps spokeswoman Casondra Brewster.

Earlier this spring, the Corps told Congress that the existing grout curtain — essentially a wall of cement and clay — only extends 475 feet in length and allows the dam to be safely filled to about 54 percent of its capacity. The Corps sought an immediate influx of cash to add another 650 feet to this underground wall and to sink it to a depth of 200 feet.

"I'm ecstatic," said Kent Mayor Suzette Cooke. "I know it was a tough request to make at this point, but this is an issue about lives and economic stability. We needed it."

The dam was so weakened by heavy storms in January 2009 that the Corps announced last summer that it was simply unable to hold back as much water as it does most winters. As a result, Seattle District Col. Anthony Wright said he might have to release water during winter rains and intentionally cause a major flood that could wash over tens of thousands of residents and businesses from Auburn to Tukwila.

In September Wright said the chance of flooding could be as high as 1 in 3, causing a panic among businesses and homeowners who sought insurance and, in some cases, relocation plans. By late fall engineers had made temporary fixes that increased the dam's capacity, prompting Wright to suggest odds of flooding had dropped to 1 in 25. And the rainy season was dry enough that dam operators didn't need to push their luck.

"While we have been very fortunate with a mild winter, I don't know anyone who thinks we're going to be that lucky again," Cooke said. "This gives us some breathing space, and certainly gives our business community more promise for the future."

The Corps has material and crews ready to start shortly after Congress approves the emergency appropriation package with the money in it. The additional fix could take six to 10 months to finish.

But even that would only last a few years, as heavy rains weaken and erode grouting material.

"We'll have geologists monitoring the grout curtain to see how it's holding up," Brewster said. "The plan would be to get a permanent fix in before it wears out."

A permanent fix could cost up to $450 million and take three to five years to complete, which is why Gov. Chris Gregoire, Cooke and other mayors from the Green River Valley were in Washington, D.C., last week lobbying White House officials.

Craig Welch: 206-464-2093 or cwelch@seattletimes.com