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Site Specificity of Bedload Measurement Using an aDcp

Author(s): C. D. Rennie; P. V. Villard

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Keywords: Bedload; ADcp; Acoustic measurement; Calibration; Particle velocity; Gravel; Sand; River

Abstract: Concurrent measurements of bedload transport velocity (v) from the bottom tracking feature of an acoustic Doppler current profiler (aDcp) and bedload transport rate (gb) from conventional pressure difference samplers are presented. Study sites include both gravelbed and sand-bed reaches of the Fraser River. Differences in correlation between v and gb amongst the contrasting environments are attributed to variations in both the bedload calibre and aDcp operating parameters. As expected, similar values of v are associated with lower mass transport rates in a sand-bed than a gravel-bed reach. Longer averaging times are required to achieve a good correlation in the data from the gravel-bed reach, likely due to the stochastic nature of bedload entrainment in gravels and the resulting heterogeneous bedload velocity field. Bedload transport is modelled using both shear stress models and a kinematic model that utilizes the estimated bedload velocity. The standard shear stress models provide poor matches to the measured bedload transport rates: the sand-bed data are overpredicted, and the gravel-bed predictions correlate poorly with the measured. Use of the kinematic model yields an estimate for the product of bedload concentration and bedload layer depth. This work highlights the potential for acoustic techniques for estimating bedload.


Year: 2003

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