Longitudinal Grain Sorting by Current in Alluvial Streams

The longitudinal current sorting of graded sediment is analysed by use of a sediment transport formula developed recently by Engelund and Fredsøe (1976). The analysis yields that for a given longitudinal profile of a river, the longitudinal variation in mean grain diameter and the grain distribution curve is unique determined by the sediment input and water discharge. No requirement concerning an ultimate equilibrium state of the bed elevation is introduced. The analysis yields that the mean grain size will decrease as the slope of the river decreases and further, that originally logarithmic normally distributed sand will tend to be logarithmic hyperbolic distributed after sorting.