Spatial heterogeneity of near-bed hydraulics above a patch of river gravel

Abstract

The spatial heterogeneity of fully turbulent, near-bed flows above gravel river beds is examined using a realistic replica of a natural gravel patch in a large flume. Three-dimensional velocity time series were obtained at four heights (0.008-0.1 m) above the local bed in each of 99 closely spaced verticals for three flows of increasing intensity. The spatial heterogeneity of time-averaged velocities and root-mean-square velocity fluctuations increases under stronger flows and closer to the bed. However, streamwise velocity becomes spatially homogeneous at a distance from the bed of between 2-4 times the median bed elevation. Heterogeneity in the direction of the velocity vector is independe..