I've written this in several threads now, but in response of Aunt Bee's request, i'll rehearse it here.
Note the highlighted area in the map above which refers to the Atchafalaya basin. This was once the course of the Mississippi River. Several hundred years ago--in one thread i mistakenly wrote 17th century, but i believe it may have been the 16th century, and i may be wrong about that, it's twenty years since i researched this--a huge log jam formed from a giant deadfall of trees. This could have been from another hurricane. At any event, it blocked the course of the river, and the Mississippi entered the bed it now occupies, more or less. However, the Atchafalaya basin is where the river "wants" to run. In the 19th century, Henry Shreve invented a means of removing snags from the rivers, particularly the Mississippi, and he was given a commission in the Army, and took charge of the Corps of Engineers Mississippi navigation project. He started on the Red River in Louisiana, and also cleared a path for the Atchafalaya River. Baton Rouge and New Orleans were both well-established towns by then, and of course, an object of the project was to improve navigation for those towns. No one gave much thought to the course of the Mississippi, however.
When d'Iberville established a settlement on Lake Pontchartrain in 1699, and his brother de Bienville established New Orleans in 1718, occassional flooding was not a problem, both because they could afford to ignore the water in low-lying areas, and because the volume of water in the river was not as great. Most could quickly drain off into Lake Pontchartrain (named for Louis XIV's Navy Minister at the time of the settlements). Subsequently, however, the building of levees on the Mississippi and its tributary rivers has dramatically increased the volume of water in the current bed. When Shreve cleard a portion of the log-jam in the Atchafalaya, centuries of silting assured that the water flowed into the Mississippi, rather than the reverse. But steady action by the Mississippi, combined with the increase of the volume of water, began to erode the bed of the Atchafalaya basin, and the Mississippi was poised to re-enter its old bed. The Atchafalaya is growing, it now has absorbed the outflow of the Red River. In 1963, the Corps built the Old River Control Structure to keep the Mississippi out of the Atchafalaya basin (referred to by hydraulic geologists as the Old River). This is an array of structures about fifty miles northwest of Baton Rouge. It requires constant, expensive maintenance, as the greater flow of the Mississippi constantly undercuts the structures. But the Corps has had a mandate from Congress to maintain the status quo, as there is now a huge corridor of refineries and chemical plants (using refinery output) between Baton Rouge and New Orleans. Sea-going tankers can pull up to the shore near Lake Pontchartrain (separated from the sea by a narrow strip of land), empty their holds into "tank farms," from which river barges can fill, and take the canals through New Oleans--chiefly the 17th Street canal, which was the site of the major, catastropic collapse of the levee in the current disaster--and then head into the river for the short trip up to the corridor and the refineries.
Therefore, the sensible thing to do would seem to be to blow up the Old River Control Structure, and let the Father of Waters go where he list. However, not only is there a human political factor promoting the status quo, there is a large corporate lobby who will want a return to the
status quo ante.
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