Good Thinking

Floating barriers reduce wave erosion on levees

Floating barriers reduce wave erosion on levees
The USDA's floating wave barrier system
The USDA's floating wave barrier system
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The USDA's floating wave barrier system
The USDA's floating wave barrier system

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.

Raum Bances
I just wrote to the USDA. It seems obvious to me that if you are going to spend money and effort on dissipating 75% of wave energy, you should consider absorbing it instead to produce electricity.
Even if the energy absorbed isn\'t that much, the community can have the installation pay for itself over time and still win.
Julien Couvreur
"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."
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...
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New Orleans was founded by a Frenchman named Sieur de Bienville in 1718. Why he thought a mudflat and river delta a few inches above sea level was a great place to have a city...
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..
Adrian Akau
It doesn\'t make sense to have 40,000 people cooped up in any structure unless it would be absolutely necessary. Studies, for example, have shown that humans become somewhat detached from reality when the live above ten stories. It is better for them to be closer to the soil.

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.

Land zones in Hawaii are rated on a 1-9 scale for volcanic risk. Prospective property buyers may determne in advance the chances of having their land covered by lava by using this scale.
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The River is much higher than the city. You have to look up you see ships sailing by instead of looking at street level even when the River is very low but when it gets up to around 30 ft as it has twice in the last five years that is about 40 feet above the city level so you can see what an enormous task it is to contain the river. The Corps also closed off the old Miss Gulf outlet thanks to public outcry, which in my opinion was a major blunder. That was the main way for flooding to leave out of the city without pumps. Now it all will have to be pumped out which was futile with no electricity or the pump houses under water. I have worked that area on barges for years and know the river and all the canals on both sides. They desperately need to rebuild Industrial Locks as it is almost a 100 years old and would probably never withstand another Katrina which if it failed would allow the River to get into the city.