Green River levees hold after heavy rain

The Green River, possibly the state's most closely watched waterway the past two years, didn't rise close to a level likely to cause major flooding.

Heavy rain and water releases from the damaged Howard Hanson Dam triggered close inspections of levees Monday by the Army Corps of Engineers, King County and valley cities, but government agencies said there was no danger of water overtopping the earthen levees.

"We still have quite a bit of freeboard," the corps' flood-team leader, Amanda Ogden, said as she watched water swirl around the trunks of trees usually above water level at Brannan Park in Auburn.

The dam kept water flows in the river well below flood level because the reservoir was nearly empty when the deluge began and the storm hit hardest north of the Green River, said Casondra Brewster, spokeswoman for the corps.

Low-lying parts of Southeast Green Valley Road east of Auburn had water on the roadway and warning signs were posted but the road wasn't closed, King County transportation officials said. The road and rural properties along it flood routinely in storms that don't cause problems downstream, in heavily populated areas protected by levees.

The river runs through Auburn, Kent, Tukwila and Renton.

Brewster said the Corps of Engineers emptied Hanson Dam to less that 1 percent of its capacity before the storm, as is standard practice at the start of the rainy season.

The corps reduced the amount of water it holds behind the earth-and-rock dam after troubling amounts of water and sediment were found to be seeping through an abutment after a January 2009 storm in which water behind the dam reached its highest-ever level.

Interim repairs to the dam last year reduced seepage and gave engineers confidence to increase the amount of water the dam can hold. That increase in capacity has drastically reduced the chance of flooding.

Work has begun on a $44 million permanent fix authorized by Congress this year. Repairs are due to be completed by mid-2012.

The amount of water released from the dam Monday was intended to raise the flow in Auburn to no more than 9,000 cubic feet per second, the level that triggers inspections of levees and warnings of floods in areas not behind levees.

But the level topped 9,600 cubic feet Monday afternoon.

"It's an inexact science" because engineers can't predict with precision how much water will flow into the river from tributaries below the dam, Brewster said.

Levees are in danger of overtopping at around 12,400 cubic feet per second.

Keith Ervin: 206-464-2105 or kervin@seattletimes.com