资源环境科技发展态势分析平台

To explore the causes of history-dependent sediment transport in rivers, we use a 19-year record of coarse sediment transport from a steep channel in Switzerland. We observe a strong dependence of the threshold for sediment motion ((c)) on the magnitude of previous flows for prior shear stresses ranging from 104 to 340Pa, resulting in seasonally increasing (c) for 10 of 19years. This stabilization occurs with and without measureable bedload transport, suggesting that small-scale riverbed rearrangement increases (c). Following large transport events (>340Pa), this history dependence is disrupted. Bedload tracers suggest that significant reorganization of the bed erases memory of previous flows. We suggest that the magnitude of past flows controls the organization of the bed, which then modifies (c), paralleling the evolution of granular media under shear. Our results support the use of a state function to better predict variability in bedload sediment transport rates.

Plain Language Summary Fluvial bedload transport governs river channel evolution and has important implications for river restoration efforts, aquatic habitats, and water quality. This fundamental sediment transport process is typically modeled independently of prior flow history, despite previous observations suggesting its influence. We evaluate the role of past flows in moderating channel stability with a unique, long-term data set from a Swiss mountain stream. We find that the onset of bedload transport has memory of past flow magnitude, where small to intermediate past flows build channel stability. High-magnitude flows disrupt this memory and can destabilize the channel bed. These results challenge the assumptions of widely used bedload transport models and suggest that predictions of erosion in river channels may be improved by accounting for the effects of prior flows.