Floating barriers reduce wave erosion on levees
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.
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Even if the energy absorbed isn\'t that much, the community can have the installation pay for itself over time and still win.
That may be an incomplete or insufficient root cause analysis. According to a documentary I was watching last week, the cause one degree further is that the natural protection against floods and hurricanes were eroded after the levees interfered with the cycle. The natural buffer that protected the city became useless...
So if you want to blame someone for flooding in New Orleans, blame the French. ;)
What\'s causing the land south of the city to go away is the river has been hemmed in with levees for so long, the sediment it carries can\'t be deposited all along the coast.
Subsidence, erosion and pumping of groundwater is making a large area, with New Orleans on top of it, slump into the Gulf.
One way to correct the problem would be to cut several canals through the city so the river can start redepositing sediment to the south.
The next step would be to do to New Orleans what Seattle did starting in 1889. the streets were walled in and filled up 12 to 30 feet to get the city above high tide so it wouldn\'t flood.
With technology available now, the building in New Orleans could be jacked up to the new street level and the space below filled in solid. New service pipes, wires etc would be easy to install above the existing streets before filling up to the new level.
It\'d be a gigantic project, but something like it will have to be done or eventually there won\'t be any buffer zone south of New Orleans and nothing will be able to be done to stop it from flooding as it falls into the Gulf of Mexico..
Secondly, why beat a dead horse. Everyone knows that the land area is sinking because it is formed out of mud brought down by the Mississippi. Why reconstruct in an areas known to have long term downward displacemtne.
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