For many incised channels, one of the most common strategies is to install some hard structures, such as grade-control structures(GCSs), in the riverbed to resist further incision. In this study, a series of experiments, including both steady and unsteady flowconditions, were conducted to investigate the scouring process downstream of a GCS. Three distinct phases, including the initial,developing and equilibrium phases, during the evolution of scour holes were identified. In addition, a semi-empirical method wasproposed to predict the equilibrium scour-hole profile for the scour countermeasure design. In general, the comparisons betweenthe experimental and simulated results are reasonably consistent. As the studies on temporal variation of the scour depth at GCSscaused by floods are limited, the effect of flood hydrograph shapes on the scour downstream of GCSs without upstream sedimentsupply was also investigated experimentally in this study. Based on the dimensional analysis and the concept of superposition, amethodology is proposed to simulate the time evolution of the maximum scour depth downstream of a GCS for steady flows.Moreover, the proposed scheme predicts reasonably well the temporal variations of the maximum scour depth for unsteady flowswith both single and multiple peak. Copyright © 2012 John Wiley & Sons, Ltd
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