Experiments on dispersion of tracer stones under lower-regime plane-bed equilibrium bed load transport

A common approach for estimating the bed load transport rate in gravel-bed streams is to relate it to deterministic channel-averaged driving parameters and corresponding resistance properties of the bed material. Notwithstanding the proven success of this approach in modeling various morphodynamic scenarios, it does not contain the mechanics necessary to relate the bulk sediment transport rate to the displacement patterns of individual particles. Experiments on entrainment, transport, and deposition of tracer stones in a flume described here were designed to address this issue. Predictors of statistics of bed elevation fluctuations at short timescales, total and elevation-specific particle entrainment rates, particle step lengths, mean and associated probability density function for particle virtual velocity, and thickness of the active layer were developed. The working hypothesis tested in this paper is that the statistics of tracer displacements can be related to channel-averaged hydraulic parameters, and thus linked to macroscopic aspects of bed load transport.