Trying to maintain a city 20 feet below sea level.
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Nope...
New orleans averages 6 feet below sea level, its highest point is 20 feet above sea level, about 65% of the city lies below sea level.
https://www.reference.com/geography/far-below-sea-level-new-orleans-690d1df79f841966
Another site I looked up said 8 feet, and apparently part of it sank after being built, it was all originally above sea level according to yet another article.
https://www.worldatlas.com/articles/how-much-of-louisiana-is-below-sea-level.html
Worldatlas.com says 8 feet.
I originally thought the real number was 12 feet, I thought that was what I looked up after Katrina but I guess my memory is not as good as it once was...
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thought i heard that on the weather channel....guess i suffer from the same as you!