Hydraulic Geometry Analysis of the Lower Mississippi River

The hydraulic geometry of the Lower Mississippi River is primarily the product of the action of natural flows acting on the floodplain materials over centuries and millennia to form an alluvial forming a channel. However, the modern channel has been modified by engineered channel improvements performed as part of the Mississippi River and Tributaries (MR&T) project. Channel improvement features include meander cutoffs, levees, diversion structures, bank stabilization, and low training dikes, which have been constructed to enhance flood control, stabilize the channel, and provide sufficient depth for navigation even at times of low water. The shape and form of the modern channel have been further influenced by morphological responses to artificial stabilization and training. Historically, morphological response involved bank erosion, siltation and some recovery of sinuosity lost due to artificial cutoffs, though more recently bank erosion, channel migration and planform evolution have all but ceased as ACM revetments now extend along a great proportion of the banklines. Substantive legislation for the MR&T project, and the initiation of the construction program, began following the catastrophic flood of 1927, and this event marks the start of the modern era in terms of channel form and process in the Lower Mississippi River. Since that time, channel dimensions and geometries have evolved under the influence of natural flows, direct engineering interventions and dynamic adjustment driven by process-response feedback loops linking flow hydraulics and channel morphology. Previous studies have documented the stage and slope adjustments on the Lower Mississippi River, but the associated changes in hydraulic geometry have not yet been fully investigated. In principle, hydraulic geometry analysis could be undertaken using comprehensive and annual hydrographic surveys of the river.

The original document contains color images. Prepared in cooperation with School of Georgraphy, Univ. of Nottingham, Nottingham, UK. Purchase request no. W90C2K9474-EN-01.