(November 17, 2009)
It's a mean old levee, cause me to weep and moan
It's a mean old levee, cause me to weep and moan
Gonna leave my baby, and my happy home
The lyrics to the 1929 blues classic “When the Levee Breaks” refer to the cataclysmic flood that began when heavy rains pounded the central basin of the Mississippi River in summer 1926. Swollen to capacity, the Mississippi broke out of its levee system in 145 places, flooding 17 million acres, and affecting an area the size of New England. Nearly a million people were displaced.
The levee failures in New Orleans during Hurricane Katrina are, of course, fresher in the American mind.
If it keeps on rainin', levee's goin' to break
If it keeps on rainin', levee's goin' to break
And the water gonna come in, have no place to stay
The challenge is to change that tune: to develop the technology to quickly seal a levee breach and reduce floodwaters through the opening within four to six hours of detection—before the water can do major damage.
Enter Wil Laska of the Science & Technology Directorate (S&T), the research arm of the Department of Homeland Security. Laska has sought out innovative technologies from industry, academia, and government to meet this challenge. Any proposed system, he dictated, 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.
“The thing is,” Laska deadpans, “there’s an effective structural material that’s readily available during floods…Water.”
He found four technologies that met his requirements, and on Nov. 9, 2009, all of them passed their second test at the U.S. Department of Agriculture’s Agriculture Research Service, Hydraulic Engineering Research Unit in Stillwater, Okla. The facility is used by the Army Corps of Engineers to test hydrology equipment and study water flow, dams and levees.
The largest technology, proposed by the Army Corps of Engineers Engineering Research and Development Center in Vicksburg, Miss., is a large balloon or tube—light enough to be transported by helicopter and flexible enough to adapt to a wide range of environmental situations. When launched or dropped, the engineers hypothesized, the tube would in quick succession fill with water, float on the flood currents to the breach, and adhere to the breach in the earthen berm or levee that had failed.
It worked.
Dubbed the Portable Lightweight Ubiquitous Gasket (PLUG), the tube of non-stretch fabric is dropped into the floodwaters and an attached pump rapidly fills it to 80 percent 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.
Monday’s PLUG demonstration was about 30 per cent larger than the ¼ scale model that was first successfully tested in September 2008. The Stillwater site is currently the only facility that can provide the water flows needed—125 cubic feet per second for several minutes.
While the PLUG system is designed specifically for narrow, deep breaches, several other solutions tailored for other types of levee breaches were also tested on Nov. 9:
- 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 to be used as a rapidly emplaced surge or flood gate.
Oh cryin' won't help you, prayin' won't do no good
Oh cryin' won't help you, prayin' won't do no good
When the levee breaks, mama, you got to lose
Engineers could be on their way to writing a less bluesy version of a 90-year-old song:
When the levee breaks, mama, you may need a PLUG.
Background
There are roughly 14,000 miles of levees owned and maintained by the U.S. Army Corps of Engineers and an estimated 85,000 miles of privately owned and operated levees. Most are more than 50 years old, and many were built 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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