Soil Erosion Processes and Sediment Sorting at Low Flow Rates

There is a need to describe sediment sorting where the on-site and off-site effects of soil erosion are studying. There is general agreement among researchers that sediment leaving an area is finer than that of the soil under surface erosion. But in some cases, it has been observed that the coarser particles transported at rates greater than the finer one. This paper describes experiments on different soil types in which the time variation in size distribution of the exiting sediment is measured. The objective was to investigate the processes that control the size distribution of the sediment at the low flow rates. The experiments were carried out on the three soils in the 1 x 6 m flume of Griffith University's large rainfall simulation facility, with overland flow confined to uniform rectangular rills pre-formed in the soil bed. The results supported a selective pattern (bimodal) for transporting of the particles of various size classes, with peaks at the finest class and the size class of 1-2 mm. The particles between 0.1-0.5 mm appeared to resist against transportation. It seems that the presence of different transport mechanisms acting on various size classes (suspension-saltation and rolling) and differences in resistance to transportation (transportability) of various size classes are responsible for selectivity in transportation at the low flow rates