Morphological changes of the Lower Mississippi River: Geomorphological response to engineering intervention

During the twentieth century, the planform and profile of the Lower Mississippi River from Cairo, Illinois, to New Orleans, Louisiana, have been transformed by a series of engineering modifications. These include steepening of the long profile by removal of the most sinuous bends, extensive bank stabilization, and regulating sediment movement by dyke field construction. Prior to these modifications, the Lower Mississippi River adjusted its morphology in the planform, long profile and cross-section. Planform adjustment has, however, effectively been negated and other adjustments are now constrained. Nevertheless, analysis of hydrographic surveys between 1949 and 1989 demonstrates that geomorphological response during the post-cutoff period remained complex. Morphological adjustments involved phased patterns of aggradation and degradation, together with changes in cross-sectional form, and in the number, size, location and shape of pools and crossings. Greatest changes occurred in the early post-cutoff period (1949-64) upstream from Vicksburg, Mississippi, but were accompanied by complementary changes elsewhere which propagated downstream. The combined set of responses may be interpreted with respect to a dynamic equilibrium in which the river responded to additional energy created by the cutoffs by increasing and adapting flow resistance over various scales and time periods. This study helps resolve paradoxes from previous analyses, and has significance for interpreting past engineering impacts and for suggesting future management strategies for the Lower Mississippi River. Copyright (c) 2005 John Wiley & Sons, Ltd.