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Many Levys are too short to contain the worst flooding and replacement is a long and costly process that can literally take decades to complete.
I propose an inflatable levy cap system that would be attached to the tops of existing levies as a stop gap measure until replacement can be undertaken.
Similar
in appearance to an airplane wing these barriers are attached to the water facing wall of the levy, with the wide area at the top , as the water rises it presses the bottom of the barrier into the levy to aid in sealing and support, the upper portion extends a small amount(say 12") above the leavys upper edge, thus providing the critical difference between a breached levy and one that holds.
Longer term such a system would allow newer levys to cope with freak events, unanticipated by designers.
Observations on the response to Katrina
http://houstonstrat...nse-to-katrina.html
"Let me add to that by floating another seemingly simple idea... emergency inflatable barriers. And perhaps even a redundant inflatable levee system that runs along the Lake that can be activated ahead of storms like Katrina" [angel, Jan 14 2008]
(?) WIPP
http://www.uk-fc.co.../info.php?p=5&pno=0
Water inflatable property protection [oneoffdave, Jan 14 2008]
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The typical levee breach is not caused by overtopping, but rather through seepage and structure failure. |
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As I understand most of the levy failures in New Orleans occurred due to either over toping and the resulting erosion or outright structural failure some of which was attributed to seepage, most was due to poor engineering or inadequate construction. |
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This problem was reported in this mornings news in relation to expected changes due to global warming. The category seemed the most appropriate for this topic, though it is misleading. |
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Ah. Katrina. Yes - a lot of overtopping failures there. Demonstrates that there can almost never be a levee system where the cost of construction is less than the cost of damage averted - for the Miss. delta levee system to have been sufficient to prevent N'orleans flooding, it would have to have been ridiculously expensive and extensive. All mitigation works are essentially a compromise. The 'freak events' are actually anticipated by designers, then discounted because they are freak events and too expensive to engineer protection against. |
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I'm also just a teeny bit sceptical about how a linear inflatable structure of anything over a few centimeters in height is going to not collapse under the force of a river several kilometers wide in full flood. |
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(sp: Levee. It's only a levy if it's taxed. And it's never a leavy.) [Insert Led Zeppelin reference here.]
Incidentally, a Gooogle search for "inflatable levee" returns seven hits. I've linked one, but there's reference to "Lafourche wary of paying inflatable-levee bill ", but the item is behind a news-site registration wall. There's a PDF as well which also mentions it. |
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There are several flood barriers that you 'inflate' with water that roll with the flood pressure adding significant height to defences. They do need constant water pressure against them to keep them in place however, so are no good with sea or flash flooding, only fluvial. |
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[admin: fixed in title.]
[quietly waiting for the inevitable post about Inflatable Levi's Extension.] |
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I'm not sure it's a good idea to have something that's inherently buoyant as the last line of defence against rising water levels - but perhaps some hydraulic system (like the WIPP thing linked by [oneoffdave])that used the water pressure at the bottom of the barrier to raise a flexible (read relatively inexpensive) barrier a few extra inches might be better approach. |
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But then would it be inexpensive? I don't know the relative costs of good old fashioned earthworks (requiring a fleet of dumptrucks and a convenient source of earth) vs a relatively fiddly manufactured solution - especially over such a wide area. |
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//'m not sure it's a good idea to have something that's inherently buoyant as the last line of defence against rising water levels - but perhaps some hydraulic system (like the WIPP thing linked by [oneoffdave])that used the water pressure at the bottom of the barrier to raise a flexible (read relatively inexpensive) barrier a few extra inches might be better approach// |
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That was kind of what I was going for here hence the shape. I figured you would add air to the system if you expected to use it otherwise it remained uninflated. |
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Systems exist in Holland, IIRC but they're not trivial or portable yet.. Might work, but not simply yet.. |
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The WIPP system is fairly portable. Comes in a trailer and can be deployed by 2-3 people. |
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What, no inflatable Chevy's? |
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//Demonstrates that there can almost never be a levee system where the cost of construction is less than the cost of damage averted// |
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Katrina costs are probably going to run into the hundreds of billions, so I'm not sure about your math. |
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The New Orleans levees failed from overtopping, percolation, and shoddy sheet pile driving. And the fact that some of them were filled with seashells. |
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And they will fail again. Putting more stuff on top pf them for the water to push against just isn't going to help much. |
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// isn't going to help much // |
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Sadly, this is true. Regrettably, it will be equally difficult to persuade the San Franciscans to move away from their lovely fault system, the Floridians to absent themselves from their Hurricane zone, the Neapolitans to forswear their view of Vesuvius (despite the rumblings from Pozzuoli and the Phlegrean Fields), or just about any damn fool from building their house on a flood plain ....... |
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