In preparation for potential Green River flooding, Boeing is building an 8-foot wall around a building at its Renton Longacres campus.

The 4,700 feet of military-grade HESCO walls, originally designed to protect soldiers from gunfire and grenade blasts, appear more like military fortifications than the traditional sand-bag walls.

“The best thing to do is to hope for the mildest case and prepare for the worst,” Boeing spokeswoman Cindy Wall said. “There is a flood risk at this point.”

The Longacres facility hosts flight simulators for its customers, expensive and complex equipment.

“We’re looking at moving certain materials to higher floors,” Wall said, adding that there’s a chance Boeing could move the machines along with some servers to a different facility.

“We still need to protect the data,” she said.

The 3-foot-wide walls are made of metal meshing and woven polypropylene fabric. The 15-foot long barriers, which are tied together at each end, are then filled with about 8 1/2 cubic yards of sand each, Wall said.

Most of the wall will be one-barrier thick, except in one area where the terrain drops. At this place it appears that the wall will be three barriers wide or about 9-feet wide.

Currently, the first level of the 4-foot-high wall is well under construction with plans to add a second layer.

The City of Renton is allowing businesses to build 4-foot temporary walls without a permit, but they’re requiring permits for anything above that, said city spokesperson Preeti Shridhar.

So far Boeing, has only received permission to build a wall around the Customer Service Training Center Building, the northern most building on campus, said Alex Pietsch, administrator for the city’s Department of Community and Economic Development.

“The buildings at Longacres are the least likely to be impacted under the modeled scenarios. They only face flooding in the worst case (25,000 cfs) model,” Pietsch said.

There is about a 1-5 percent chance that the river will flood that badly.

However, scenario models show that retention ponds that sit on Boeing property could be 6 to 10 feet under flood waters, if the Green River flows at 17,600 cfs, which is about a 5-10 percent chance.

The cfs measurement stands for cubic feet per second and gauges the amount of water flowing down the river. The measurement is taken in Auburn.

The Kent Space Center, which is in the flood-plain area, is also getting 12,000 feet of the walling and at least double wide.

“Our Kent facility is a major communications area for the Northwest,” Wall said. “It also houses a lot of our department of defense programs.”

The City of Renton is requiring that the temporary structures not requiring a permit also don’t block emergency exits. At Longacres, the wall stops at entrances to parking lots.

“They need to put it up in such a way that we can access the buildings,” Wall said.

The Army Corps of Engineers is offering about a 12-hour notice to businesses and residents in Renton, before flood waters begin to rise. This about the time the construction crews will have to build the remaining wall.

Boeing has offered some of its space at Boeing Field to the cities for storing sand bagging materials, Wall said.

“We’re working really closely with the cities of Renton, Kent, Tukwila and the corps,” she said. “This is a pretty massive effort.”

The Army corps is giving the City of Renton 500,000 sand bags and 10,000 SuperSaks, but city officials haven’t decided where they plan on storing their materials.

“SuperSaks are like giant vinyl bags, they are 4-feet high and have handles and can be moved,” she said. “We are considering using these for secondary containment and possibly to provide protection for some of our city facilities.”

The city is also looking at purchasing a $26,000 machine that can fill about 2,000 sand bags per hour, Shridhar.