Critical shear stress is a pivotal parameter that describes the bedload transport and riverbed stability. Recent studies indicate that different interevent periods in gravel-bed streams can lead to a realignment of riverbed structures, thereby disrupting the bedload transport. In this research, a series of flume experiments were conducted to study the effect of stress history on the critical shear stress of bedload transport in a gravel-bed channel. The results reveal the temporal-spatial variation patterns of critical shear stress. The critical shear stress has an increased trend after interevent with low flow and long duration. Conversely, a decreasing trend in critical shear stress observed after low flow and short duration conditions. After interevent durations with medium to high flow condition, no matter the duration, critical shear stress shows a decreasing trend. A significant positive correlation between the flow magnitude of the interevent period and the critical shear stress of the subsequent flood period is shown. Besides, critical shear stress has a significant spatial variation pattern on the gravel bed due to the presence of microtopography as revealed by the correlation analysis results among the spatial density of microtopography with different protrusion heights, riverbed statistical parameters, and critical shear stress. Moreover, the stress history, by adjusting the position of fine particles on the riverbed surface through different magnitudes and durations of the interevent period, affects the spatial density of the microtopography, thereby influencing the critical shear stress. The conventional bedload transport equations are deficit by only considering the riverbed slope or standard deviation of bed surface elevation. An optimization of the critical shear stress calculation method, based on parameter correlation analysis, is proposed, potentially enhancing the calculation accuracy of bedload transport in mountainous rivers.

中文翻译：

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应力历史对砾石河床流中床载运临界剪应力的影响


临界剪切应力是描述河床载荷传输和河床稳定性的关键参数。最近的研究表明，砾石床溪流中不同的事件间期会导致河床结构的重新排列，从而破坏河床荷载的运输。本研究开展了一系列水槽试验，研究了应力历史对砾石床通道中床载运输临界剪切应力的影响。结果揭示了临界剪切应力的时空变化模式。临界剪切应力在低流量和长持续时间的相互作用后呈增大趋势。相反，在低流量和短持续时间条件下观察到临界剪切应力的下降趋势。在中高流动条件下的事件间持续时间之后，无论持续时间如何，临界剪切应力都呈下降趋势。结果表明，事件间期的流量大小与后续洪水期的临界剪切应力之间存在显著的正相关关系。此外，由于微地形的存在，临界剪切应力在砾石河床上具有显著的空间变化模式，不同突起高度的微地形空间密度、河床统计参数和临界剪切应力之间的关联分析结果揭示了临界剪切应力。此外，应力历史通过不同大小和持续时间的事件间期来调整细颗粒在河床表面的位置，从而影响微地形的空间密度，从而影响临界剪切应力。传统的河床载荷输运方程仅考虑河床坡度或河床表面高程的标准差是亏缺的。 提出了一种基于参数相关性分析的临界剪应力计算方法的优化方法，可能提高山区河流床载输运的计算精度。