Erosion, deposition and basin‐wide variations in stream power and bed shear stress

Abstract

Field data from four separate locations indicate that the rate at which river channel gradient decreases downstream is fundamentally different in areas of long‐term erosion and deposition. Gradient (S) and distance from the drainage divide (x) are related such that S is proportional to xφ. In areas of deposition φ<−3, whilst in areas of erosion φ>−1.1. These differences produce downstream increases and decreases in stream power and bed shear stress which also coincide with areas of erosion and deposition. This is the first time that such a basin‐wide coincidence has been demonstrated.A strong positive correlation between stream power, bed shear stress and bedload transport rates has been clearly shown by previous empirical studies of loose‐bed channels. It is proposed that large‐scale patterns of erosion and deposition in alluvial basins result from downstream changes in bedload transport rates, produced by the observed trends in these two parameters. If this proposal is to be fully tested, further work is needed to assess the affects of downstream fining of bed material, short‐term fluctuations in discharge and downstream exchange of particles between the suspended load and bedload.