Environmental-physical dynamics of birds foot deltas:

• there are river, tide, and wave dominated deltas, and mixtures between these three major shaping forces. The Mississippi is a river dominated delta. These deltas are characterized by fingers of river channel sediment that build out, and hence are known as birds foot deltas.
• main river splits into distributary channels, but one usually dominates.
• normal channel meander migration.
• episodic lobe abandonment and switching (often large changes during major flood events). This behavior can be modeled on a small scale in a stream table.
• associated siltation and shoreline progradation in one area and shoreline retreat in another.
• movement of the saltwater-freshwater interface and associated biotic changes.
• compaction and subsidence.

The geologic history of the Mississippi delta:

• Quote from John McPhee, The Control of Nature: " The Mississippi River, with its sand and silt, has created most of Louisiana, and it could not have done so my remaining in one channel. If it had, southern Louisiana would be a long narrow peninsula reaching into the Gulf of Mexico. Southern Louisiana exists in its present form because the Mississippi River has jumped here and there within an arc about two hundred miles wide, like a pianist with one one hand -- frequently and radically changing course, surging over the left or the right bank to go off in utterly new directions. Always it is the river's purpose to get to the Gulf by the shortest and steepest gradient. ... By the nineteen-fifties, the Mississippi River had advanced so far past New Orleans and out into the Gulf that it was about to shift again, and its offspring the Atchafalaya was ready to receive it. By the route of the Atchafalaya, the distance across the delta plain was a hundred and forty-five miles -- well under half the length of the route of the master stream."
• Uniformitarianism in the Mississippi River Delta: Relationships Between Present Day Landscapes and Holocene Geologic History by Chad Cooper Senior, Professional Geology Department of Geosciences Mississippi State University.
  

The Atchafalaya control structure and New Orleans.

• link to USGS CMG InfoBank Geology School: Mississippi River. Includes short film clips, including one on the Old River Control Project.
• the 1973 flood.
• link to Army Corp map of control structures.

Quotes from John McPhee, The Control of Nature:

"Rabalais works for the U.S. Army Corp of Engineers. Some years ago, the Corps made a film that showed the navigation lock and complex of associated structures built in an effort to prevent the capture of the Mississippi. The narrator said, "This nation has a large and powerful adversary. Our opponent could cause the the United States to lose nearly all her seaborne commerce, to lose her standing as first among trading nations . . . . We are fighting Mother Nature . . . . It's a battle we have to fight day by day, year by year, the health of our economy depends on the victory."Big question - for how long will the Army Corp be able to maintain the status quo?

"As we traversed the Mississippi, the depth, which was being sketched by a stylus on graph paper, dropped steadily and kept on dropping the closer we came to the bank. We were only a few swimming strokes from shore when the depth reached a hundred feet. It was notable that the riverbed was fifty feet below sea level more than three hundred miles from the mouth of the river, but what particularly astounded me was the very great depth so close to the west bank. It showed the excavating force of a tremendous river. The foundations of skyscrapers are rarely that deep. And this was the bend where the water swung off and into Old River Control - a bend armored with concrete where the Mississippi might break free and go to the Atchafalaya."

• USGS Mississippi and Atchafalaya Deltas Study.
• Louisiana DNR Atchafalaya basin program.
• National Audobon Society's description of the Atchafalaya basin.

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