Processes of Water Erosion

Summary

This paper considers some Australian research on the various processes of erosion and deposition involved in net loss of soil in water erosion. Detachment of soil by rainfall is non-size-selective, and in the presence of the highly size-selective process of deposition, a sediment rich in fine sediment is initially produced by these processes. The nature of the changing character of the soil surface sediment is discussed. It is suggested that the development of a deposited layer coarser than the original soil may be the reason for the commonly-observed general decline in sediment concentration toward a constant value under steady rainfall. A distinction is made between entrainment and the re-entrainment of sediment deposited during the erosion event, though both processes are due to the same shear stresses between overland flow and the land surface. New ways of mathematically representing these processes are developed, and the results compared with some other previously-reported methods. Approximate equilibrium theory is outlined for the simultaneous operation of entrainment, re-entrainment and deposition processes. This approximate theory is extended to allow interpretation of erosion data measured on a ridge-furrow system, and applied to the experiments of Meyer and Harmon (1985).