We present results from flume experiments in which an 8% steep channel with longitudinal width variations and step-pool morphology was subjected to sediment feed pulses of different magnitude and frequency under constant water discharge. The channel response to these pulses included (a) large bedload transport rates, (b) bed aggradation, (c) fining of the bed surface, and (d) continuous formation and collapse of steps. In between pulses, the bed surface coarsened, and bedload transport rates dropped by several orders of magnitude. Steps continuously formed and collapsed during and shortly after the pulses, but their stability increased when the sediment feed was turned off. High pulse magnitude enhanced step formation, while low pulse frequency (i.e., long interpulse period) enhanced step stability. We back-calculated the threshold for motion based on measured bedload transport rates and bed shear stress. Changes in the threshold for motion were much larger than changes in bed surface slope. By accounting for energy dissipation through the effective slope based on flow resistance partitioning, a better prediction was obtained. The threshold for motion decreased following sediment pulses then increased immediately after and fluctuated until the next sediment pulse. Our results indicate that longitudinal width variations and episodic sediment supply are primary controls on the evolution of step-pool channels. Sediment feed magnitude affects mostly morphological changes, while sediment feed frequency controls channel stability.

中文翻译：

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浅析浅析沉积物供应如何影响实验阶梯池水道中水道形态、底泥输送和水道稳定性的演变

我们展示了水槽实验的结果，其中一个具有纵向宽度变化和阶梯池形态的 8% 陡峭通道在恒定排水量下受到不同幅度和频率的沉积物进料脉冲。对这些脉冲的通道响应包括 (a) 大的床荷载传输速率，(b) 床的聚集，(c) 床表面的细化，以及 (d) 台阶的连续形成和坍塌。在脉冲之间，床表面变粗糙，床负载传输速率下降了几个数量级。在脉冲期间和之后不久，台阶不断形成和坍塌，但当沉积物供给关闭时，它们的稳定性增加。高脉冲幅度增强阶跃形成，而低脉冲频率（即长脉冲间隔）增强阶跃稳定性。我们根据测量的床荷载传输速率和床剪切应力反算了运动阈值。运动阈值的变化远大于床面坡度的变化。通过基于流阻划分的有效坡度考虑能量耗散，获得了更好的预测。运动阈值随着沉积物脉冲而降低，然后立即增加并波动直到下一个沉积物脉冲。我们的结果表明，纵向宽度变化和间歇性沉积物供应是阶梯池通道演变的主要控制因素。沉积物进料量主要影响形态变化，而沉积物进料频率控制通道稳定性。运动阈值的变化远大于床面坡度的变化。通过基于流阻划分的有效坡度考虑能量耗散，获得了更好的预测。运动阈值随着沉积物脉冲而降低，然后立即增加并波动直到下一个沉积物脉冲。我们的结果表明，纵向宽度变化和间歇性沉积物供应是阶梯池通道演变的主要控制因素。沉积物进料量主要影响形态变化，而沉积物进料频率控制通道稳定性。运动阈值的变化远大于床面坡度的变化。通过基于流阻划分的有效坡度考虑能量耗散，获得了更好的预测。运动阈值随着沉积物脉冲而降低，然后立即增加并波动直到下一个沉积物脉冲。我们的结果表明，纵向宽度变化和间歇性沉积物供应是阶梯池通道演变的主要控制因素。沉积物进料量主要影响形态变化，而沉积物进料频率控制通道稳定性。运动阈值随着沉积物脉冲而降低，然后立即增加并波动直到下一个沉积物脉冲。我们的结果表明，纵向宽度变化和间歇性沉积物供应是阶梯池通道演变的主要控制因素。沉积物进料量主要影响形态变化，而沉积物进料频率控制通道稳定性。运动阈值随着沉积物脉冲而降低，然后立即增加并波动直到下一个沉积物脉冲。我们的结果表明，纵向宽度变化和间歇性沉积物供应是阶梯池通道演变的主要控制因素。沉积物进料量主要影响形态变化，而沉积物进料频率控制通道稳定性。