Rates and processes of bank erosion were evaluated for reaches of two alluvial, equiwidth to wide bend, point bar streams in Iowa: East Nishnabotna River and Des Moines River. The evaluation was made using historical records (airphotos, maps, and streamflow records), field measurements, and soil analyses. The erosion rates were correlated with channel characteristics such as width, depth, curvature, arc angle of channel centerline, channel slope, friction factor, and degree of vegetation on the banks. The correlation was studied using a meander flow model developed by the author. The meander flow model simulated the velocity distribution in the bends and the location of the erosion occurrences. Estimates were made of total sediment influx to the rivers from cutbank erosion.
Dynamic features of the flow in a 180° constant‐radius, recirculating laboratory channel are studied. The width‐depth ratio and radius‐width ratio of the channel are 16 and 5.4, respectively, and the sediment is sand with median grain diameter and geometric standard deviation of 0.3 mm and 1.45, respectively. The particle densimetric Froude number is 6.5. Individual components of the momentum equation are measured, and their relative effect on the momentum balance is evaluated. It is found that flow accelerations, notably downstream acceleration of the downstream and cross‐stream velocity components, induced as a result of change in channel curvature at the entrance to the bend have a significant effect on the flow processes in this bend. The cross‐stream velocity gradients are relatively insignificant. The curvature change affects the flow and bed topography in a manner similar to that in which a driving force affects an underdamped oscillating system. The findings are used for an evaluation of available bend flow models.
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