The Mississippi River drains a watershed of 1.85 million square miles, or 41 percent of the U.S., stretching from the Appalachian Mountains to the Rocky Mountains across 31 states and two Canadian provinces. One of North America’s longest rivers, it flows 2,340 miles from Lake Itasca, Minn., to the Gulf of Mexico below New Orleans, and its floodplain covers more than 30 million acres. With more than 250 tributaries, and with distributaries in Louisiana that spread water and silt across broad areas, it has long enriched farmland along the waterway. The river is divided into the Upper, Middle, and Lower Mississippi, with the lower section extending from the Ohio River to the Gulf of Mexico, where the river reaches a mile in width at some points and is bordered by high bluffs, man-made levees, oxbow lakes, swamps, marshes, and cities that developed along a major commercial corridor. The Mississippi has shifted course many times in geologic history; its current basin was shaped by the Laurentide Ice Sheet at the end of the last ice age about 11,700 years ago, and its present course dates to about 800 to 1,000 years ago, when it shifted from the Lafourche Delta. The stretch between Vidalia and Natchez became an important crossing for early settlers and a docking place for flatboats, steamboats, and other water transportation. After the Flood of 1927, the U.S. Army Corps of Engineers built levees, outlets, and control structures to reduce catastrophic flooding in the lower Mississippi region, and to expand the levee system at Vidalia, the entire city was moved a mile west in 1938. The present waterfront river walk stands on an abandoned downtown street, and the first bridge there was built in 1940 as automobile and truck transportation grew in importance. Across the river from Vidalia, the loess bluffs at Natchez, formed by windblown soils deposited millennia ago, provide elevation that protects the city from flooding, though the soil’s erodible nature has created large gullies and ravines along the opposite bank. In this area, the river’s flood stage is 48 feet, compared with 27 feet at Donaldsonville and 17 feet at New Orleans.
