Local scour induced by upstream riverbed level lowering

摘要

Upstream riverbed level lowering causes local scour occurring downstream bed, which may endanger the channel stability and structures safety. In this paper, a series of experiments were conducted to investigate the characteristics of the induced local scour. Meanwhile, a non-equilibrium sediment transport model and a diffusion model were proposed to theoretically predict the scour profiles. The experiment results show that a local scour hole preserves shape similarity during the scouring process. Therefore, formulas based on dimensional analysis and the measured data were developed to describe the temporal variation of the scour hole, including the maximum scour depth, location of the maximum scour and the longitudinal scour length. These parameters were found to be strongly related to the dimensionless excess friction velocity. Comparisons between the theoretical models and the measured data show that the scour process is divided into two stages by a critical time. The maximum scour depth in the earlier and later stages can be well described by the non-equilibrium sediment transport model and diffusion model, respectively. Furthermore, the instantaneous bed profiles near the bottom of the scour hole and further downstream fit well with the non-equilibrium sediment transport model and diffusion model, respectively.