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WA considers possible dam failure

Water seeping through Green River dam prompts warnings, disaster planning

BY ZACHARY HOFFMAN | SEATTLE | September 3, 2009

If a Washington State dam fails this winter, the resulting flood could cause more than $3 billion in damage to residents and businesses in the Green River Valley say officials, who are concerned about water now leaking through the Howard Hanson Dam.

The dam is currently only able to operate at 75 percent capacity due to increased seepage caused by record rainfall from last January. If prolonged rains come again this year, the excess water could surge down river to areas that have not seen flooding since the dam was built.

“An entire generation has lived without flooding,” said Lynne Miller of King County Emergency Management. “There hasn’t been any flooding damage because of the dam and the levees for 50 years now.”

Patricia Graesser of the U.S. Army Corps of Engineers (USACE) said, “We raised water levels to typical flood levels (tiered pool raise); we found that above 1155 feet above sea level the rate of seepage was significantly higher.”

The question for cities in the Green River Valley is would it be fiscally sound to temporarily move critical infrastructure and people during flood season? The valley could lose $46 million a day in economic losses.

On Monday, the King County Council gave Executive Kurt Triplett the ability to declare a state of emergency before floodwaters come into the valley.

Miller said, “We have a pre-comprehensive help outreach strategy, compiling brochures and letters to give resources about the dam and flooding, pushing flood insurance and coordinating personal alert systems -- every landline could get a phone call.”

The Federal Emergency Management Agency (FEMA) is also involved in public outreach by launching a very aggressive flood insurance campaign, not only to the Green River Valley, but also to those who suffer from flooding across the state.

Family Insurance Agency’s Michael McCaughan in Kent, WA, said in years past no one bought flood insurance unless it was mandated; this week he has sold 12 policies.

“There are a lot of people living in the valley who are not doing anything about it," McCaughan said. “There are 25,000 people, and I sold 12.”

One Farm Bureau Insurance agent said when the waters rise, people will flock to agents to buy policies, but they do not realize that there is a 30-day waiting period. It is like trying to buy life insurance after you have been diagnosed with terminal cancer.

Graesser said, “The dam is an earthen dam and on the right side (right abutment) the dam is tied into landslide material, water moves through that material and it always has.”

“The landslide material is made up of big boulders, sand, clay, pebbles and all sorts of material; gaps are there,” said Graesser. “We don’t want water to move through the abutment and move material.”

Injecting grout slurry into the gaps in the abutment will help temporarily fix the excessive seepage while more permanent fixes are being explored.

“If the dam itself (the constructed structure) was the problem, we have construction drawings and specs to know the problem and be able to fix it,” Graesser said.

“If we don’t get a big flood this year we need to prepare for one next year,” said Miller. “Next year we are going to be talking about this again, every year until there is a permanent fix we’ll be talking about this.”

Nearby, in Walla Walla, WA, the USACE has also classified the seepage problem at the Mill Creek Dam as Class 1 “urgent and compelling.” During normal operations, the reservoir contains only five to ten percent of capacity and there is no evidence to suggest an emergency situation exists.

“The Corps is screening all of its (635) dams and assigning safety classification ratings. The new dam safety classification system, entitled Dam Safety Action Category (DSAC), spotlights dams and navigation locks with compelling problems first,” according to a USACE news release.

The Clearwater Dam in Missouri is another dam that has been a Class 1 rating through the DSAC. Ratings under the DSAC range from 1 to 5, DSAC-5 being the safest.

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