"It almost looked like a tidal wave coming across the land, " recalls Rick Gerstel, a resident of Gulfport.

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That means, in practice, that they can be deployed only some 50km from land, which is better than tidal gauges, but not ideal.

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Ocean hits are worse than land hits, not just because of immense tidal waves, but because of the vast quantities of super-heated water vapor and dust that spread from the impact to shroud the entire Earth.

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One proposal: a set of giant movable gates to be built on the land separating Lake Pontchartrain from the Gulf that when closed could block tidal surges, and when open, improve water flow.

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