With restrictions on the water-pool level behind the Howard Hanson Dam, Kent Mayor Suzette Cooke, Chair of the King County Flood Control Zone District Advisory Committee, took a proactive step to reduce potential flooding this winter in the Green River Valley. “Our first line of defense should be to fight the flood at the levee – not in the Valley,” Cooke declared. “It is much less costly to prevent flooding in the first place, than to suffer the financial and emotional expense of cleaning up after a flood.”
Cooke requested staff begin purchasing giant sandbags for placement on top of the Green River levee system within Kent’s city limits. The city is coordinating its efforts with the US Army Corps of Engineers, King County and the other Valley cities of Auburn, Tukwila and Renton.
According to Larry Blanchard, Kent’s Public Works Director, these structures are a proven method to assist in flood-fighting. “Giant sandbags have been successfully used around the country to manage the flow of water,” Blanchard said. “They would be up to 3 feet high and weigh 3,500 pounds each. They are easily installed and can be placed on top of Kent’s levees to increase their height.”
A recent engineering survey of the levee elevation indicated with every one foot increase in height of the river bank, the Green River gains an additional 1,000 CFS (cubic feet per second) capacity. “The giant sandbags will provide additional capacity in the Green River, allowing us to protect ourselves up to 13,900 CFS with three feet of free board space above the river’s main flow level,” Blanchard said.
The city previously considered using giant water-filled bladders, or aqua-dams, to line the levee system but determined that sandbags are more sturdy. Aqua-dams may be used as a second line of defense.
Kent officials are still preparing for potential flooding this winter due to concerns about the Howard Hanson Dam after sink holes were discovered in its right abutment last January. The U.S. Army Corps of Engineers, who has responsibility for the dam, has warned that it will not be able to hold back as much water as in the past during heavy rains, therefore increasing the risk of flooding downstream.
“Even with giant sandbags in place along the levees, every resident and business in the Green River Valley needs to purchase flood insurance and devise a plan for evacuation,” Cooke said. “Emergency measures are linked to our web site, www.choosekent.com, and being distributed through numerous meetings and mailings. While the dam itself is not under our jurisdiction, the city is doing all that it can within its authority to prevent a disaster.”
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