SEATTLE -- Hurried repairs at a badly weakened flood-control reservoir have greatly reduced but far from eliminated the risk of flooding this winter in the Green River Valley near Seattle, the U.S. Army Corps of Engineers said Thursday.

The region has been preparing for flooding ever since a torrential storm in January weakened an abutment to an important upstream dam that holds back the Green River. Residents and businesses have been piling up sandbags and the corps has been working around the clock on repairs to shore up the abutment. Most of the repairs were completed within the past week.

Col. Anthony Wright, the corps' Seattle district commander, provided an update Thursday on the dam repairs. He said there was now a 1-in-25 chance that a storm would force the corps to release enough water from the dam's reservoir to cause a flood downstream in the Green River Valley. The odds of widespread flooding in the valley improve to 1-in-32 when all the sandbagging and flood-protection efforts are factored in.

Previously, the Corps of Engineers said the chance of widespread flooding was 1-in-4. While that is "a substantial change in the risk for the people downstream," the danger is still very high and the preparations in the valley were critical, Wright said.

"It was really bad before and it's now just bad," he said.

Residents, businesses and local governments in the long, flat valley have been working feverishly to fortify their property and the levees along the winding river against a potentially catastrophic flood during the winter rainy season. The corps has estimated that beyond the human cost, a flood could cause $4 billion in damage.