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Pressure fluctuations and gravel entrainment in rivers

Author(s): G.M. Smart; H.M. Habersack

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Keywords: Entrainment; pressure fluctuation; sediment transport; bed load

Abstract: Near-bed, sub-bed and uplift pressure fluctuations measured in New Zealand gravel bed rivers were found to have near Gaussian frequency distributions. At measurement sites the standard deviation of near-bed pressure fluctuations was approximately 3 times the local time–averaged bed shear stress. Pressure structures in the flow decayed rapidly. For the measured rivers, the near-bed pressure decorrelation time was approximately half the flow depth to shear velocity ratio. Measurements made in the middle of a flat plate in the plane of the bed and beneath the bed showed that advecting pressure fluctuations can create a vertical pressure differential in the bed surface layer that is sufficient to entrain gravel particles. Additional pressure fluctuations can be generated within mobile beds.


Year: 2007

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