Image: Howard Hanson Dam
Ted S. Warren  /  AP
Workers adjust a drill being used to strengthen the Howard Hanson Dam, near Ravenswood, Wash. The dam began showing disturbing signs of vulnerability after a torrential rainstorm in January, and officials have been warning residents to buy flood insurance, stow valuables in safe places and be ready to flee.
updated 9/28/2009 4:00:27 PM ET 2009-09-28T20:00:27

For nearly 25 years Kathy Gladden has lived about 100 feet from the Green River, a normally placid stream that meanders past the many homes, offices, warehouses and shopping malls that blanket the area.

Now, she and thousands of others face the all-too-real prospect that the river will gush past a leaky upstream dam and swallow up their homes once the rainy season starts in November, devastating a heavily developed area in the Seattle suburbs that is a vital hub of commerce.

The Howard Hanson Dam began showing disturbing signs of vulnerability after a torrential rainstorm in January, and officials have been warning residents to buy flood insurance, stow valuables in safe places and be ready to flee.

King County has declared a state of emergency that allows it to seek federal reimbursement and speed up work to bolster levees, while the Army Corps of Engineers bought 400,000 sandbags and other flood-fighting materials in the round-the-clock fight to save the dam.

"I can't bear it. It's awful," said Gladden, 72, who hates the idea of having to leave her mobile home park and its tight-knit community. "I never even heard of the Howard Hanson Dam until the trouble started."

Dam completed in 1962
The dam, located in the Cascade foothills east of Seattle, has prevented major floods in the Green River valley since it was completed in 1962. That changed when last winter's heavy rains weakened a hillside next to the dam.

A record 15 inches of rain fell in 12 hours on the Green River's upper watershed in January, sending torrents into the 235-foot-high dam's reservoir. The reservoir rapidly filled 6 feet higher than ever before.

The dam held the water back and remained sound. But at the high water levels, engineers saw worrying signs within the dam's right abutment, a 450-foot-wide pile of rock deposited by a huge landslide 10,000 years ago.

As a temporary fix, the corps is spending $8.9 million to inject grout into the abutment, forming a shield to lessen the seepage. Without such work, Col. Anthony Wright, the corps' Seattle District commander, said there would be a 1 in 3 chance this winter for flooding in the Green River Valley.

Image: Howard Hanson Dam
Ted S. Warren  /  AP
Workers try to strengthen the Howard Hanson Dam, near Ravenswood, Wash.
But Wright won't know by how well the fixes will work until tests are performed. Wright said he's "going to do everything possible to prevent flooding downstream, but this structure's ability to do what it's done well for 50 years is hampered and therefore they have a higher risk of that flooding."

The possibility of catastrophic flooding has caused considerable anxiety in the flood-prone area.

Billions of economic activity
Besides homes and apartment complexes, the valley has hundreds of offices — including headquarters for Boeing Commercial Airplanes — sprawling shopping malls, factories and what the corps says is the third-largest warehouse area in the nation.

"There's $50 billion of economic activity in the valley, and no one takes that for granted," says Kent city spokeswoman Michelle Witham.

About 25,000 people live on the valley floor, which includes parts of the cities of Kent, Auburn, Renton and Tukwila, but hundreds of thousands work, shop or travel there daily. State officials say 22,000 people might have to be evacuated in a flood.

Under 6 feet of water
In a flood, county officials estimate Kent's downtown could be under 6 feet of water, swamping businesses, city offices and the county's regional justice center, which includes courtrooms, offices and a jail that can house up to 1,384 inmates. Already, the county has relocated its election offices from Renton, just south of Seattle, to ensure it can count votes from November's election in the event of flooding.

"I don't understand why they didn't repair it earlier," said Nathan Sorrell, 30, a truck driver who recently bought flood insurance for his Kent home. "This is people's lives. It's not going to be 'Oh, there's water on my lawn.' We're not going to have water, sewer, power. It's almost like a little Katrina."

Mamie Brouwer, Hanson Dam's program manager, said the problems weren't known until January's high water. She said the corps hopes to have a permanent fix — a concrete wall the length of the abutment and reaching down to bedrock — designed within a year and finished after two years of construction — a project that could cost up to $500 million.

County wants millions for repairs
County Executive Kurt Triplett has asked the County Council to approve $8.4 million to strengthen 40 miles of levees, though he acknowledges there isn't enough time to complete the work before winter. He also wants the cash-strapped county to borrow more than $32 million for such things as protecting a critical sewage treatment plant, building a flood-proof wall around the justice center, relocating offices and, if necessary, evacuating jail inmates.

"It is the right thing to do even it the worst-case scenarios don't happen," he said. "Too much is at stake."

Residents are hoping the floodwaters hold off, but preparing for the worst.

Marie Manson has lived in Auburn since 1923 and remembers flooded roads and her father having to constantly pump water from the house before the dam was built. The 89-year-old has bought flood insurance and moved important documents and valuables to safe spots.

"I'll deal with it when it comes," she said. "I don't know what else to do."

Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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