Selective bedload transport during the degradation of a well sorted graded sediment bed

The paper presents an analysis of the composition of bedload transport and changes to bed structure and topography during three graded sediment degradation experiments. The analysis suggests that variations in channel hydraulics and active layer composition alone may not explain the observed reductions in sediment transport. Further, the experiments appear to cover a crucial range of mean bed shear stresses for armouring studies, ranging between a condition of passive winnowing, to one of more active armour development in which the coarse grains play a role in determining bed structure. This indicates that the active layer concept, commonly applied in computer models of graded sediment transport, may be limited in its application.