The City of Renton received its first shipment of giant sandbags Monday that it will use to protect city buildings and possibly roads against flooding of the Green River.
The U.S. Army Corps of Engineers is providing Renton with 2,000 of the supersized sandbags that come in various sizes, measured in feet, that can weigh tons when filled with sand.
“You want to fill those up fairly close to where they are used,” said Gregg Zimmerman, the city’s public works directors.
The city will have a portable sandbag-filling machine that it can move to where the big bags are needed. The City Council approved the purchase of the $29,000 “Megga Bagger” Monday night.
The sandbags initially are delivered to a Boeing warehouse in Tukwila near Boeing Field, where they will be stored, along with sandbags intended for other cities in the Green River Valley.
The city picked up the big bags Monday morning and delivered them to the city’s Fire Station 14 on Lind Avenue in the city’s southwest warehouse district.
Today (Tuesday), about 500 tons of sand were delivered to the station, home to the city’s fire training center and an expansive open area. The city also has 1,500 tons of sand at its shops in the Highlands.
To save money, the city will use sand used on roads in last winter’s storms and then recycled, plus recycled soil, to fill the bags.
First Station 14 is the location of what Zimmerman called the city’s flood-management staging area. The city will place some of big bags around the fire station on Monday, even though it sits on a rise in the Valley floor and is likely to be threatened only in a severe flood.
The city also will use the fire station grounds to fill the regular-sized sandbags – it will receive about 500,000 of those from the corps – for use in the city and by Renton residents. Information when citizens can get those sandbags will be available soon.
Renton and other cities in the Green River Valley, including Kent, Auburn and Tukwila, are spending hundreds of thousands of dollars to prepare for potential flooding of the river. The right abutment of the Howard Hanson Dam was damaged in lasts January’s massive storm, forcing the corps to keep storage lower than normal in a major storm in the reservoir.
Those higher flows could lead to flooding in the Green River Valley, which now stands at about a one in four chance of happening, according to the Corps of Engineers, which owns and operates the dam.
The corps is making an initial fix to the dam’s abutment, filling voids in the abutment with grout. Those repairs are expected to be done in early November. Long-term repairs could take years.
Because it’s unknown how long the flood threat will last, the city is taking steps to ensure the sandbags do not deteriorate too quickly, according to Zimmerman.
“Our intention is that we only want to do this once,” said Zimmerman.
The city will cover the sandbags with plastic to protect their burlap material, he said. The city will keep an eye on the sandbags once they are placed, he said.
Cities along the Green River, along with the corps, are placing the super-sandbags along the river now. The bags will raise the protective levees enough to prevent flooding at 13,900 cubic feet per second. The higher artificial levees also have a cushion of three feet of freeboard.
Now, the corps keeps the maximum flow of the Green River at 12,000 cubic feet per second, as measured in Auburn. A river level of 13,900 cfs wouldn’t cause any flooding in Renton. Flooding becomes possible when flows reach about 17,600 cfs.
The big sandbags are the primary defense against flooding, with the intent that the bags are placed to protect all the low-lying areas, no matter what city the Green runs through, said Zimmerman.
But Renton and other cities are planning second lines of defense. What Kent or Tukwila do could help protect Renton, too, so Renton’s plans for secondary protection are dependent on the plans of other cities, Zimmerman said.
