![]() Meandering is the result of an intricate interaction of hydrological, hydrodynamical, geomorphological and ecological processes. Meander migration through bank erosion and accretion results in reworking of the floodplain and valley widening. Lowland rivers seldom follow a straight course but typically meander in their alluvial plain. The results suggest that large shallow rivers have the most dynamic meandering behavior, while the occurrence of stabilized meanders seems to be favored in narrow rivers. The relative importance of these three hydrodynamic processes depends on hydraulic, geometric, and sedimentologic conditions, which is consistent with the large variance in observed migration rates. Overall the results suggest that secondary flow saturation and outer-bank cells tend to inhibit meander migration, whereas inner-bank separation may enhance migration. The effects of flow separation at the inner bank are found to be strongly conditioned by flow-sediment interactions, which lead to an increased scour depth near the outer bank and increased velocities near the toe of that bank. ![]() ![]() The experiments reveal that outer-bank cells exist near steep as well as shelving banks and amplify with increasing steepness and roughness of the outer bank, and especially with increasing curvature. For outer-bank cells and inner-bank flow separation, the analysis relies on experimental findings from flume studies in channels with fixed and mobile beds. This process is called the saturation of the secondary flow. Predictions from a reduced-order hydrodynamic model show that nonlinear hydrodynamic interactions limit the growth of the secondary flow. This paper examines three hydrodynamic processes in sharp bends with fixed banks and discusses their morphological implications: secondary flow saturation, outer-banks cells, and inner-bank flow separation. The migration rate of sharp meander bends exhibits large variance and indicates that some sharply curved bends tend to stabilize.
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