Beyond the Forecast: Danger looms in Green River Valley

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by GARY CHITTIM / KING 5 News

Bio | Email | Follow: @gchittimK5

KING5.com

Posted on November 4, 2009 at 8:30 PM

Updated Wednesday, Nov 11 at 4:38 PM

KENT, Wash. - There's an added danger looming over tens of thousands of Puget Sound-area residents this year, and probably for years to come.

The rain this fall is getting a lot more attention this year. Instead of just settling in for another rainy season, residents of the Green River Valley are scooping up sand and stacking bags. They're beginning a new way of life without the Howard Hanson Dam.

The first signs of trouble showed up back in January when residents below the dam noticed water in places it shouldn't be.

"Boy it just rose to levels in the creek and across the road that we just haven't seen before," said one resident.

We soon learned the cause - the US Army Corps of Engineers was rapidly releasing from the Howard Hanson Dam. 

They were worried about a problem that showed up when a series of storms raised the level of the reservoir to record levels.

The Corps determined the depression was probably harmless, but dye tests during the investigation revealed something inside the dam tunnel that was much more menacing.

"The dye exited into the tunnel in approximately 90 minutes," said project manager Mamie Brouwer.

Water that should take several hours to seep through the earthen section of the dam was flowing through in minutes. The Corps now had a major problem.

"There is a potential that if this has significant movement or loss of stability, the water could go around the dam. That is the biggest concern we have," said Col. Anthony Wright of the Corps of Engineers.

The Corps says if that happens, the entire structure could be vulnerable to a failure capable of leaving the Green River Valley, thousands of residents and one of the state's largest economic engines flooded under several feet of water.

To prevent that they are racing to inject the so-called dam abutment with cement to plug holes and plans are underway to construct a concrete support wall behind the dam.

But since none of that can be tested this flood season, the Howard Hanson Dam cannot be trusted.

The Corps will release potential flood waters rather than risk losing the whole dam.

That leaves much of the valley in a very precarious situation. If we get normal to dry season, we might avoid any flooding at all. If things get really wet or if we get a series of strong storms like last year, the river will jump the banks that have prevented major flooding for decades.\

Floods were commonplace in the old days before the dam. Back then residents of the sparsely populated valley knew what to do.

"They'd call us up in the middle of the night and say, 'come get the horses,'" said one longtime resident.

Things are different now. When the dam went in, the valley took off and became a jam-packed center of commerce of communities that have never experienced life without the Howard Hanson Dam. 

Evacuation routes are in place in affected communities, including Kent, Renton, Auburn and Tukwila. Blue signs were posted a few weeks ago.

King County plans on fighting water with -- water. Last month workers at the south treatment plant in Renton filled large bags with water to use as a barrier. If the plant floods, more than 1 million homes could experience plumbing back-ups.

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