The paperpresents some results of a field study designed to examine flow structure over bedforms. It also quantitatively compares these results to previous laboratory investigations of flow over fixed bedforms. In this study measurements of turbulence were obtained in a small river in Illinois, USA over a fine spatial grid of sampling points above a mobile sand wave and a molded replica. Flow remained attached to the riverbed within the troughs for both bedforms, but pattern of stacked wakes, similar to that observed in laboratory studies, was clearly evident in the vertical profiles of turbulence statistics. The spatially non-uniform flow over the mobile bedform appeared to approximate more closely turbulence equilibrium than the flow over the fixed bedform. In as much as propagation velocity of bedforms is an index of transport rates of bed material, results of field and laboratory studies should be compared only for similar bed-material transport rates.
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