Safety concern eases with new levee technologies

Tuesday, April 13, 2010 @ 04:04 PM gHale

After the levee failures in New Orleans during Hurricane Katrina, the challenge now confronting experts is to develop the technology that can quickly seal a levee breach and reduce floodwaters through the opening within four to six hours of detection—before any water can do major damage.

That is where Wil Laska of the Science & Technology Directorate (S&T), the research arm of the Department of Homeland Security, comes in.

Laska is on the hunt for innovative technologies from industry, academia, and government that can meet this challenge. Any proposed system had to not only be capable of quickly closing breaches, but also be suitable for scenarios in which the breach may be difficult or impossible to reach with conventional construction equipment, he said.

“The thing is there’s an effective structural material that’s readily available during floods…water,” he said.

He found four technologies that met his requirements, and in November they all passed their second test at the U.S. Department of Agriculture’s Agriculture Research Service, Hydraulic Engineering Research Unit in Stillwater, Okla. The Army Corps of Engineers uses that facility to test hydrology equipment and study water flow, dams and levees.

The top technology, proposed by the Army Corps of Engineers Engineering Research and Development Center in Vicksburg, Miss., is a large balloon or tube. The tube is light enough to carry by helicopter and flexible enough to adapt to a wide range of environmental situations. The engineers said when they launched the tube, it would quickly fill with water, float on the flood currents to the breach, and adhere to the breach in the earthen berm or levee.

The “Portable Lightweight Ubiquitous Gasket (PLUG)” is a tube of non-stretch fabric officials can drop into floodwaters and an attached pump rapidly fills it to 80% capacity—a bubble of air inside keeps the tube from sinking beneath the waters. Positioned upstream, flood currents pull it toward the breach. The incompressible nature of water and the unyielding fabric turn the tube into a rigid plug that conforms to the breach and seals it.

The PLUG is mainly for narrow, deep breaches, however other technologies tailored for other types of levee breaches are also under development:

  • A smaller version of the PLUG–designed to prevent the over-topping flow of a long, shallow breach.
  • The Rapidly Emplaced Protection for Earthen Levees (REPEL)—designed to protect against erosion during the intentional overtopping of levees, mitigating erosion from the back slope of a levee which over time could cause a deep breach.
  • The Rapidly Emplaced Hydraulic Arch Barrier (REHAB)—an arched tube designed to hold back a surge of water during a levee breach repair, to seal breaches obstructed by debris or other structures, and can see use as a rapidly emplaced surge or flood gate.

The U.S. Army Corps of Engineers owns and maintains 14,000 miles of levees and an estimated 85,000 miles of privately owned and operated levees. Most are more than 50 years old, and many went up in agricultural areas now deeply embedded in the urban landscape.

Levees fail for many reasons, not all of which are weather related. For instance, California’s major concern is liquefaction of their levees during an earthquake. And some Midwestern levees have failed under sunny skies due to erosion caused by the long-term effects of previous high water and flood conditions.

The intended primary customer of the PLUG would be local levee boards and State Emergency Management Agencies.

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