Velocity fluctuations in a steep, coarse-bedded river were measured in flow depths ranging from 0.8 to 2.2 m, with mean velocities at middepth from 1.1 to 3.1 m s-1. Analyses of synchronous velocity records for two and three points in the vertical showed a broad range of high coherence for wave periods from 10 to 100 s, centering around 10-30 s. Streamwise correlations over distances of 9 and 14 m showed convection velocities near : mean velocity for the same wave periods. The range of coherent wave periods was a small multiple of predicted 'boil' periods. Correlative fluctuations in synchronous velocity records in the vertical direction suggested the blending of short pulses into longer wave periods. The highest spectral densities were measured beyond the range of coherent wave periods and were probably induced by migration of low-relief bed forms.
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Correlative velocity fluctuations over a gravel river bed