Reach classifications of the lower Mississippi River

Abstract

A classification of the lower Mississippi River into geomorphically distinct reaches provides an effective framework within which the influence of numerous morphologic variables can be analyzed. A singular realization of the river, however, requires that a statistical inference be applied to the results which provides a level of assurance to the conclusions. A nonparametric method, Multi-Response Permutation Procedures (MRPP), is employed to evaluate the significance of channel morphology variables within an a priori reach classification based upon sinuosity and valley slope. An alternative classification is proffered, generated by MRPP, which defines homogeneous subpopulations of the river as reaches for the collective response of the channel morphology variables. The numeric analyses generate a refinement, by further subdivision, of the original proposed reach structure. Within each reach the multivariate response of the system can be studied through space and time. Within the time period considered here, 1880 to 1915, the river channel became progressively wider and shallower. These trends are spatially manifest in fewer longer reaches in 1880 and more shorter reaches in 1915. This increased variability is concentrated in the areas affected by the Lake County and Monroe uplifts.