This Stratfor article explains the geopolitical importance of New Orleans and why it must be rebuilt:

"The United States historically has depended on the Mississippi and its tributaries for transport. Barges navigate the river. Ships go on the ocean. The barges must offload to the ships and vice versa. There must be a facility to empower this exchange. It is also the facility where goods are stored in transit. Without this port, the river can't be used. Protecting that port has been, from the time of the Louisiana Purchase, a fundamental national security issue for the United States.

Katrina has taken out the port -- not by destroying the facilities, but by rendering the area uninhabited and potentially uninhabitable. That means that even if the Mississippi remains navigable, the absence of a port near the mouth of the river makes the Mississippi enormously less useful than it was. For these reasons, the United States has lost not only its biggest port complex, but also the utility of its river transport system -- the foundation of the entire American transport system. There are some substitutes, but none with sufficient capacity to solve the problem.

It follows from this that the port will have to be revived and, one would assume, the city as well. The ports around New Orleans are located as far north as they can be and still be accessed by ocean-going vessels. The need for ships to be able to pass each other in the waterways, which narrow to the north, adds to the problem. Besides, the Highway 190 bridge in Baton Rouge blocks the river going north. New Orleans is where it is for a reason: The United States needs a city right there.

New Orleans is not optional for the United States' commercial infrastructure. It is a terrible place for a city to be located, but exactly the place where a city must exist. With that as a given, a city will return there because the alternatives are too devastating. The harvest is coming, and that means that the port will have to be opened soon."