Geometric and Statistical Characteristics of Bed Forms in the Lower Mississippi River

Bed forms in alluvial systems are three dimensional. The most common bed forms are: ripples, dunes and bars. Under certain flows, different bed forms may be superimposed on each other, e.g. dunes superimposed on bars or ripples superimposed on dunes. The irregularity in the bed of alluvial streams caused by the existence of bed forms produces additional flow resistance, which affects the hydrodynamics and sediment transport properties of the system. The geometry of bed forms in large alluvial, rivers such as the Lower Mississippi River exhibits both coherent and random characteristics. Average wave lengths and heights alone cannot adequately describe these bed forms. A spectral approach was used in this study to capture the periodicity and frequency distributions of the observed bed forms along a study reach in the Lower Mississippi River extending from river mile zero (Head of Passes) to river mile 234 (near Baton Rouge, LA).