In 1973, the Mississippi River was out of its banks for more than 2 mo from April to June. The thickness and the texture of overbank sediments were determined for a number of depositional environments on the Mississippi River flood plain in Louisiana. Average sediment thickness ranged from 53 cm along the natural levee to 1.1 cm in the back-swamp. The texture of deposits varied from natural levee sediments with 68 percent sand to backswamp sediments with 97 percent silt and clay. The amount of lateral erosion of bordering Pleistocene bluffs increased 271 percent over the previous 9 yr of record because of the flood. Using the rate of backswamp deposition during the 1973 flood, it is suggested that backswamp deposits in this area required 10,000 to 11,000 yr to accumulate.

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