Measurement of the spatial distribution of fluvial bedload transport velocity in both sand and gravel

Maps are presented of the spatial distribution of two-dimensional bedload transport velocity vectors. Bedload velocity data were collected using the bottom tracking feature of an acoustic Doppler current profiler (aDcp) in both a gravel-bed reach and a sand-bed reach of Fraser River, British Columbia. Block-averaged bedload velocity vectors, and bedload velocity vectors interpolated onto a uniform grid, revealed coherent patterns in the bedload velocity distribution. Concurrent Helley-Smith bedload sampling in the sand-bed reach corroborated the trends observed in the bedload velocity map. Contemporaneous 2D vector maps of near-bed water velocity (velocity in bins centered between 25 cm and 50 cm from the bottom) and depth-averaged water velocity were also generated from the aDcp data. Using a vector correlation coefficient, which is independent of the choice of coordinate system, the bedload velocity distribution was significantly correlated to the near-bed and depth-averaged water velocity distributions. The bedload velocity distribution also compared favorably with variations in depth and estimates of the spatial distribution of shear stress. Copyright (C) 2004 John Wiley Sons, Ltd.