[Gondring]

Of course, fixing that silt distribution would be very easy---just cut two "east-west" channels well up the isthmus---one from the Missippi towards the east, and one from the Mississippi towards the west.

There you go. We're on the same page now.

The reason New Orleans is below sea level is because the LAND IS SINKING, due to the huge weight of all the buildings (built on Jello), and the pumping out of groundwater. Again--nothing to do with river silt.

You got two of the three parts right. Subsidence is definitely important, but it's not a differential subsidence based on the river water holding up the river or something--water is heavy, too. It is also the silt that builds the elevation of the river up. (Plus, note that the the weight of the thickness of sediments themselves bends the lithosphere regionally, not just weight of buildings.)

Without the river containing silt, it could cut deeper into the channel and carry that load out into the Gulf...making the river lower. However, with the silt load deposited, the elevation of the river increases as the city subsides.

[cfo]

Power outages seem to have have hit almost everyone in the city, even Entergy New Orleans' command center at the Hyatt Regency Hotel next to the Superdome

[Wonder Warthog]

"Without the river containing silt, it could cut deeper into the channel and carry that load out into the Gulf...making the river lower. However, with the silt load deposited, the elevation of the river increases as the city subsides.

Uh, the river DOES "...carry that load out into the Gulf"--why do you think the isthmus got built in the first place. Add to that the fact that they dredge the river regularly to KEEP the channel open deep enough for ocean-going vessels, so I still don't see silt deposition being of any signficant consequence.

The problem is that with the isthmus "channelized" south as far as it is, the silt is deposited over the "Gulf abysss" (or whatever the name is for the demarcation between the continental shelf and "deep water", and so is lost to any possibility of "marsh-building".

[Robert A Cook PE]

IF New Orleans were sinking due to building weight, ONLY the heaviest buildings would be going down: The WHOLE AREA is lowering (a very little bit due to ground water pumping - that's what began submerging parts of Baytown TX back in the early 70's) but NOT ENOUGH water is pumped out to cause the whole rea to keep going down.

Bldg foundations ONLY spread the load out in the immediate area of the building (most of which is spreadout BETWEEN the pilings, NOT even into adjacent bldg's, (much less into adjacent city blocks!).

More important, downtown NO is a very, very small area: less than 4 square miles. Most of which is 2-4 story buildings! (Very light weight, geologically speaking. There are only a few high-rises, and something like the Long Bridge weighs more than the buildings.)