ABSTRACT
When compared to standard Shields estimations for the initial motion of sediment transport, field observations and laboratory experiments performed in steady non-uniform flows show pronounced deviations. While recognizing the importance of considering the channel’s slope influence on the critical shear stress, the discrepancies found in many experiments carried out in steady non-uniform flow conditions cannot be simply justified or explained by the dependence of the channel’s slope. This work shows that other extensions to the standard Shields approach should be considered, in addition to the channel slope. In particular, the influence of non-uniform flows on the critical Shields stress (effects of accelerating and decelerating flows) is demonstrated, as well as the effect of seepage on the critical shear stress. The great influence of the relative roughness on the transport capacity of the flow is also shown. Finally, a model that includes all these effects is suggested.
