Someone I know claims that in the years since the levies were built, the Mississippi river has deposited so much silt that now the bottom of the river is higher than the surrounding land! If that’s true, then add another arguement to the GD threads about the wisdom of trying to preserve the status quo in New Orleans.
I suspect that there is a bit of exaggeration, here. I do not recall that any of New Orleans has been identified as being more than 20 feet below sea level. The City of Nerw Orleans is a bonafide seaport. In the last day or so, the Coast Guard approved passage for “shallow” commercial vessels on the Mississippi past New Orleans with “deep” vessels scheduled for approval for limited traffic in the next day or so.
The definition of a “shallow” commercial vessel is 30 feet and “deep” vessels can go much deeper. Since the Mississippi River is still flowing as it appses New Orleans, it must be a few inches higher than sea level. This means that, unless someone can find a section of New Orleans that is more than 30 feet below sea level, the claim is baseless.
Cross-section of New Orleans
Note that the water levels displayed are to the top of the levees. To see the actual city levels, find the lines in the river and lake marked “0” and imagine a line between them. (This is sea level, not normal water levels.) However, it is from that point that the river bottom must extend downward a minimum of 30 feet. During a dry spell, the water levels will be just above the “0” mark, but the river must be sufficiently deeper to handle oceanic ships.
Nice map, tomndebb. Good looking out.
The Mississippi river at New Orleans is over 100 ft deep-far below sea level. The power of all that water flowing through that channel is amazing. In fact there is an ocean-going ship sunk at the bottom of the river. They aren’t sure exactly where it is, but it is too deep to be a hazard to shipping. (It is buried in the mud and hard to find with sonar.)
Anyone who has seen the Mississippi flowing past New Orleans would realize that there isn’t going to be any sedimentation at that point.
Right – all the levee-ing and “controlling” of the river to keep it from evolving naturally has the added effect of concentrationg all that flow through the channel (rather than diffusing it throughout wetlands).