Abstract

Alternate gravel bars usually appear in embanked gravel-bed river channels regulated by dams, causing safety risks to hydraulic structures and modifying fluvial ecology. Managing bars remains challenging and crucial for a river restoration project. Gravel replenishment is one measure to mitigate sediment deficits caused by dam regulation, while its efficiency in embanked rivers with bar morphology remains still unclear. We conducted a laboratory experiment to investigate the morphological effects of single high-flow stockpile replenishment after a flood event in a straight embanked channel characterized by steady hybrid bars. Results showed that erosion of the stockpile and sediment wave propagation mainly occurred during the high-flow period. The stockpile was laterally more eroded when the upstream sediment supply was maintained, while the sediment wave propagated further when the sediment supply was eliminated. Topographic and flow velocity data showed bar migration and suppression triggered by the forcing of the implemented stockpile during high flows regardless of upstream sediment supply during the flood. After the flood, bar morphology reappeared with maintained upstream sediment supply, while a single-thread incised channel was observed without the upstream supply. These observations suggest that sediment replenishment, combined with different upstream dam release manipulations, can strongly modify the initial bar morphology of an embanked river the efficiency of which also depends on upstream dam operations during high flows. This experiment also benefited from a detailed data acquisition plan and analysis, providing a dataset suitable for constructing and calibrating a 2D numerical morphodynamic model for future sediment replenishment design.