Argument: The Mississippi river will shift away from New Orleans
"Infeasibility of Rebuilding New Orleans". Pure Energy Systems. 23 Sept. 2005 - During a powerful flood in the late 1950s, the Mississippi River forced its way into the Atchafalaya River and the main channel began to go far to the west of New Orleans. With this flood the City of New Orleans and the ports there were threatened with being cut off from the river. The US Army Corps of Engineers was tasked with attempting to keep the Mississippi River controlled and in its old channel. The “Old River Control Structure” (ORCS) was completed in 1963 to keep 70% of the river in the old channel.
How a Port Becomes a Backwater
This set of dams worked for a while. In 1973 the river threw another enormous flood and undermined a large section of the ORCS. Since that time the river has progressively become more and more uncontrolled as the ORCS is further and further undermined. The status at this time is that another event on the river will probably cause a large part of the ORCS to disappear without a trace and the Mississippi River will finish moving west to Morgan City. This is probably going to happen within the next 20 years or so. It is probably unwise to even consider trying to stop this event which natural forces are working to bring about.
The Mississippi River is moving westward. The City of New Orleans will be cut off from fresh water, and be attached to a silted-in port of no value, attached to water that doesn’t go anywhere. This is a certainty. The only issue with this event is when. The event is going to happen shortly. If the events occur as a result of a flood rather than by deliberately managed processes, the USA may find that its precious Mississippi River port area is worthless. Even before Hurricane Katrina, the city was living on borrowed time. Its dance with the Mississippi River is soon to end.
The swamp in which New Orleans sits can only be supported by a continual influx of fresh water from the Mississippi River. The US Army Corps of Engineers damaged this process severely with canals and channels as well as by putting up dikes. The city is sinking for lack of this water. Mud deposited by floods would have rebuilt the naturally sinking land. This became painfully apparent when the city dikes broke.
In fact, as reliably reported in the Hunstville Times on Sunday September 11, 2005, breakage of the levees occurred two days before the arrival of Katrina. (Ref. ) It may have been due to seismic activity, the rhythmic pounding of resonant waves whipped up by hurricanes which precede landfall by up to two days. These resonant waves reached a solid point and cracked it. It was the new segments, made of concrete reinforced with steel, which failed.
Thus it could have been human error that flooded New Orleans. In assuming that rigidity means strength in every circumstance, did engineers fail to recognize that the whole region is more like jello than strong rock and soil? If so, the planners didn’t grasp that the barrier would have to flex along with the soft muck beneath it. Any reinforcing would have to be flexible as well, such as a fibrous or woven-link Kevlar, or some such material. In such a location, rigid reinforcing would inevitably result in breakage,
Whatever the reason for the failure, the dikes broke more than 18 hours before the storm came ashore. The US Army Corps of Engineers and the New Orleans and Lousiana Authorities all knew there was already serious flooding one day before the storm. The whole issue was that the bureaucrats argued over who was in charge and nobody did anything. Officials passed the buck back and forth until the Big Excuse arrived, both completing the flooding and distracting everyone from the issue of legal responsibility. If engineering mistakes were involved, no one in authority would announce them, as no one in charge would want to be sued for the astronomical level of financial damages, not counting loss of life.
What had been predicted to be 4 to 6 feet of floodwater was nearly 20 feet in places. The city is sinking faster than anyone believed.
Subsidence Speeding Up
With its dance with the river over, the city of New Orleans will begin to sink even faster into the ocean. This sinking is not only because of the lack of water. New Orleans is on a cliff over a mile high, part of the underlying structure of the continental shelf. Nobody can see the cliff because the ocean covers it up. New Orleans is a city on the edge of a cliff and it is oozing off the edge.
The edge of the cliff may be generally seen on a map where the river ends. The fall from this point is into the deep abyss. The taller the city builds the more it will squish the muck that supports it into the ocean depths. Its very success dooms New Orleans.
"The Case Against Rebuilding New Orleans". The Unplanning Journal. 8 Sept. 2005 - should we rebuild New Orleans?
From a Geological stand point, the quick answer would have to be no.
New Orleans, as everyone has now learned, is situated on the ground between the Mississippi River and Lake Ponchetraine in a natural delta. Constant deposition of sediment is required to sustain any delta. Without it, erosion from tidal and wave forces will eventually erode away the formation. Hurricanes can accelerate this process dramatically. Worldwide, this erosion can be observed in almost every river delta that has had its flooding action halted by damming of the upstream head waters or channelization via artificial levee construction. In New Orleans, both man made interventions affected the Mississippi River’s flow.
As concerning as that may be, the pumping of groundwater and later, oil and natural gas, further increased the rate of subsidence to where portions of the city are now more than 20 feet below sea level.
With land subsiding in the interior and eroding at the fringes, the conclusion is clear. This area is not inhabitable without significant protection and mitigation, with each year requiring greater measures (higher levees, stronger flood walls and bigger pumps).
"The Case Against Rebuilding New Orleans". The Unplanning Journal. 8 Sept. 2005 - over the long haul this area also has to fear delta-switching as well. The Mississippi, like all other major rivers undergo a process whereby the main channel periodically switches location within the delta. This process is well understood by geologists and hydrologists but ignored by most other individuals, due in large part to their infrequent occurrence. Delta switching can occur every few hundred years, when the main tributary becomes so excessively long that river water has to travel an ever longer distance to reach the sea. A longer length means the main channel flow slows compared to the other branches. Eventually one of those branches “captures” the flow of the original main channel and becomes the new main channel, due to its shorter distance and faster flow.