AN APPROXIMATION OF THE SEDIMENT BUDGET OF THE LOWER MISSISSIPPI RIVER PRIOR TO MAJOR HUMAN-MODIFICATION

A sediment budget is constructed for the Lower Mississippi River prior to the introduction of most human modifications. Components of the budget are derived from historical data including Mississippi River Commission hydrographic survey maps for the period from 1877 to 1924. A quantitative estimate of major sediment sources, sinks and storage locations in the Lower Mississippi Valley suggest that the most important sediment source was from bank caving and that at least 50 per cent more sediment was deposited in short-term channel storage than in longer-term overbank storage. The budget indicates that the proportion of sediment transported as bedload was significantly greater than previously estimated. The magnitude and variability of these sediment budget components are discussed. The results of the study suggest that prior to modifications the river was aggrading over much of its length.