The Mississippi could jump its banks in a flood and go somewhere that isn’t New Orleans, shutting off 60% of America’s grain exports.
During this year’s flood, Dr Jeff Masters posted a fascinating series of articles (pt2, pt3) on Weather Underground, describing why the river is trying to change course, how it might happen, and the impact if it did.
For the last thousand years, the Mississippi has flowed down its current path, down the middle of America and then taking a gentle left turn to New Orleans and out into the Gulf of Mexico. Geography suggests that the water should be flowing down the shorter, steeper Atchafalaya.
The only thing stopping the river from jumping its bank is the Old River Control Structure, a series of dams and floodways that contain the Mississippi and control the flow into the Atchafalaya.
The floods in the Mississippi basin are getting bigger as the river channel silts up and every big flood carries the risk that the control structure will fail.
If the Atchafalaya captures the Mississippi’s flow the consequences could be dire for New Orleans, for America, and for the world.
New Orleans would lose its fresh water supply and the port would become inoperable, costing an estimated $300 million a day.
The Port of South Louisiana is a ninety kilometer long complex, which handles over 200 million tonnes of cargo per year. The port would dry up if the river changed course, causing economic devastation until ports could be built along the new route.
The Mississippi provides access to most of America’s arable land, its catchment stretching from the Rockies to the Appalachians. The river network is one of America’s greatest assets. Shipping goods by water is about a tenth the cost of shipping goods over land. America’s farmland operates far more efficiently because it’s covered by navigable rivers.
America produces vast amounts of food for export. 60% of its grain goes out through the ports along the Mississippi and an interruption to that supply would cause global food prices to jump. Shortages in many countries would be inevitable along with the social unrest that brings.
For the whole story, read the series on Weather Underground:
America’s Achilles’ Heel: the Mississippi River’s Old River Control Structure
Escalating Floods Putting Mississippi River’s Old River Control Structure at Risk
If the Old River Control Structure Fails: A Catastrophe With Global Impact