Stratfor sums up effects of Katrina.
A simple way to think about the New Orleans port complex is that it is where the bulk commodities of agriculture go out to the world and the bulk commodities of industrialism come in. The commodity chain of the global food industry starts here, as does that of American industrialism. If these facilities are gone, more than the price of goods shifts: The very physical structure of the global economy would have to be reshaped. Consider the impact to the U.S. auto industry if steel doesn't come up the river, or the effect on global food supplies if U.S. corn and soybeans don't get to the markets.
The problem is that there are no good shipping alternatives. River transport is cheap, and most of the commodities we are discussing have low value-to-weight ratios. The U.S. transport system was built on the assumption that these commodities would travel to and from New Orleans by barge, where they would be loaded on ships or offloaded. Apart from port capacity elsewhere in the United States, there aren’t enough trucks or rail cars to handle the long-distance hauling of these enormous quantities – assuming for the moment that the economics could be managed, which they can’t be.
The rest is worth a read.