Author(s): Robert H. Meade
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Abstract: The Mississippi and its tributaries are among the most intensively engineered of the largest rivers of the world. The engineering works that have the most pervasive effects on river sedimentation are (1) dams and their impounded reservoirs, (2) bank-stabilization and channelization works, and (3) flood-control levees. High dams were constructed across major tributaries, first for hydropower, and later combining hydropower with flood control, irrigation, and navigation. High-dam construction began a century ago and continued through the 1940s mainly in the Tennessee Valley, and then, during the 1950s and 1960s, it culminated in a series of dams built across the Missouri River. Meanwhile, low-head dams designed principally to maintain navigable depths for river shipping were constructed on Ohio River, upper Mississippi River, Illinois River, Arkansas River, and Red River. Bank-stabilization works, such as revetments, pile dikes, and wing dikes, were installed to channelize the flow and to prevent lateral erosion. Flood-control levees have been constructed for centuries, beginning on the lower Mississippi during the 1700s. The levees were gradually raised in height and eventually enclosed the thousand-mile length of the Mississippi from the Ohio-Mississippi confluence to the Gulf of Mexico. Effects on fluvial sedimentation of dams and their impoundments in Mississippi River basin have been determined by six main factors: (1) initial topography, (2) geomorphic history, (3) quantities of transported sediment and (4) hydraulics of sediment transport, in the affected reach of river both before and after dam completion; (5) design of the dam and the resulting shape and size of its impoundment; (6) operating schedule of the dam, especially the timing of releases. Different combinations of these factors are available for comparative analysis within the Mississippi River basin. Levees have prevented the annual overbank deposition and storage of sediment on floodplains. Bank-protection and channelization works have locked into permanent storage the sediment that otherwise would have been repeatedly mobilized during regular flooding. The annual exchange of sedimentary material between channels and floodplains, which is a dominant feature of the sediment budgets of other large but less-engineered alluvial rivers, has been virtually stopped along the Mississippi River.
Year: 2004