DYNAMICS OF BEDFORMS IN THE LOWER MISSISSIPPI-RIVER

The size and roughness characteristics of dunes in the Mississippi Riv er are not predicted well by experimental and theoretical relations, e ven though intensive how measurements were made in the study area. Alt hough dunes increase in scale with increasing discharge of water and s ediment, the development of multiple dune sizes and nonuniform how obs cure the relationship of dune geometry to synoptic hydraulic variables . Some nonuniformity is caused by the development of large bed undulat ions from kinematic waves that can deform into compound dunes, but mos t of it is related to how convergence and divergence in pools and riff les, varying flow geometry with increasing stage, and reach-controlled relations between flow and energy loss. Even though changes of bedfor m size are not found to lag the flow changes because sand transport is large, a considerable volume of sediment is required to initiate and propagate the largest compound dunes. This means that they might be pr ofiled in different stages of growth and have a varying effect on the flow during their evolution spatially and temporally.