Motion of Single Particles in Alluvial Channels

Movements of single sand-size radioactive particles were followed in a laboratory alluvial channel. Two sizes of bed material were used with experimental conditions limited to the ripple and dune bed forms of the lower flow regime. It was found that the frequency distribution of the particle step lengths was represented very well by the gamma distribution, and the frequency distribution of the particle rest period was represented adequately by the exponential distribution. The mean step lengths related well to the stream power of the flow; however, the relation cannot be considered general because observations were limited to a single depth of flow. The mean rest period related well to the celerity of the bed forms. Tests of a one-dimensional stochastic model for sediment dispersion showed that the model predicted the mean distance traveled by the tracer particles but did not predict the rate of spreading of the tracer concentration distribution.