Floating barriers reduce wave erosion on levees
By Ben Coxworth
July 12, 2010
With all the publicity the Gulf Oil Spill is currently receiving, it’s easy to forget about another disaster from which the city of New Orleans is still recovering – the flood caused by Hurricane Katrina in 2005. That flood, of course, occurred because the levee along the city’s coastline couldn’t stand up to the assault of the storm-driven waves. Daniel Wren, a hydraulic engineer who works for the USDA Agriculture Research Service in Oxford, Mississippi, is now working on a system that might have kept that from happening. He has developed floating barriers that can dissipate up to 75 percent of a wave’s energy, before that wave reaches the levee.
To keep things in perspective, it should be noted that Wren’s system is currently being developed to protect the levees on irrigation reservoirs. While lives may not be at stake in this case, thousands of dollars in potential rebuilding work are, not to mention the lost man-hours and damage to crops that a burst reservoir would entail. Needless to say, if his system does prove effective on the farms, it’s entirely possible a much larger version could find its way onto the Louisiana coastline.
The barriers consist of two spaced, yet joined, rows of sealed hollow tubes. They float parallel to the levee, held in place between two rows of vertical pilings, driven into the bottom of the reservoir. Because the tubes can float all the way up and down the height of the pilings, they will always be level with the water’s surface, regardless of fluctuating water levels. Why two rows of tubing? It was found that while the waves would lose much of their energy when hitting the first row, they would lose more still when meeting the second.
After gathering wind and wave data from a 70-acre reservoir in Arkansas, Wren and his team simulated the conditions in a 19 meter (63 foot) wave pool back in Mississippi. There, they found that the tubes could absorb as much as three quarters of a wave’s energy.
Not only might the USDA’s barriers keep levees from bursting, but they could also substantially reduce maintenance costs – it has been estimated that unprotected reservoir levees can erode by up to one foot per year, requiring repairs within as little as five years after being built.