Flow-transport modeling and quantification of the periodic nature of bed forms in the Lower Mississippi River

Several research investigations have been conducted on the flow and sediment transport over bed forms in alluvial rivers (e.g. mean flow field, turbulence, shear partitioning, bed load transport and bed form geometry). Much of this work was either laboratory studies or small scale field investigations. Recently, advances in technology have improved the way data are collected and analyzed, e.g. flow data, velocity data and detailed bathymetric information that provide greater knowledge about the bed form geometry. Recent advances in computing power have also reduced the computational restrictions on using three dimensional numerical models in modeling flow applications to predict the temporal and spatial changes of flow and sediment environments.; The work performed in this research quantified the periodic nature of bed forms types and geometries along the Lower Mississippi River. Correlations were performed relating the hydrodynamics of the river to the bed form types and geometries. The research work showed the inability of hydrostatic numerical modeling systems to accurately predict flow separation at the bed form crest but indicated that these models could reasonably predict the out of phase relationship between the bed form and the water surface profile. Furthermore the hydrostatic models predicted the total bed resistance as adequately as the non-hydrostatic models. It was found that non-hydrostatic models are required to properly simulate flow separation at bed form crests. Models such as MIKE 3 with constant z-level vertical discretization failed to capture the observed boundary layers unless very fine grids are used. A new procedure was developed as a part of this research, in which relations and dependencies between the hydrodynamic resistance and the bed form dimensions relative to the numerical model spatial scale were derived. This procedure can be used to aid in numerical riverine model calibration and to provide a better representation of flow resistance in hydrodynamic modeling codes.