Understanding bed load impact dynamics on exposed bedrock in rivers is crucial to quantifying the erosive energy of a stream. Observations of the bed load saltation trajectories and impact energies are lacking, particularly in channels with nonplanar bed topography. In this study, we performed four flume experiments of saltating gravel to offer new insights on the dependence of particle impact dynamics on transport stage and bed topography. Our experiments used two different boundary shear stresses (τ_b = 36.5 and 25.4 Pa) and two different bed configurations, planar and nonplanar (bedrock disks uniformly oriented at 10° from the bed surface). For each experiment, we indirectly estimated the impact energies from the trajectories of particles with high‐speed video imaging and measured the erosion rates of rock samples embedded in the flume floor. The planar and nonplanar beds had negative and constant relationships, respectively, between energy delivered to the bed and transport stage. The nonplanar bed had a heavier tailed distribution of impact energy than the planar bed, which implies a greater number of rare highly erosive impacts. Probabilistic formulations of particle trajectories better predict the increase or decrease in erosion rate across experiments than deterministic regression equations. Our findings suggest that bedrock erosion models should consider a distribution of possible bed load impact energies, particularly for natural river channels that have rough surfaces.

中文翻译：

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水床冲刷能量对水槽的冲击试验对粗糙床和平面床的影响

了解河流中裸露的基岩上的床荷冲击动力学对于量化河流的侵蚀性能量至关重要。缺乏对床载荷盐化轨迹和冲击能的观察，特别是在床床地形不平坦的通道中。在这项研究中，我们进行了四个盐化砾石的水槽实验，以提供有关颗粒撞击动力学对运输阶段和床层地形的依赖性的新见解。我们的实验中使用了两种不同的边界的剪切应力（τ _b = 36.5和25.4 Pa）和两种不同的床构造，平面的和非平面的（基岩盘均匀地与床表面成10°定向）。对于每个实验，我们都通过高速视频成像从粒子轨迹间接估算冲击能量，并测量埋入水槽底板的岩石样品的腐蚀速率。平面床和非平面床在传递到床和运输阶段的能量之间分别具有负和恒定的关系。与平面床相比，非平面床具有更大的冲击能量尾部分布，这意味着大量罕见的高度侵蚀性冲击。与确定性回归方程相比，整个实验中粒子轨迹的概率公式更好地预测了腐蚀速率的增加或减少。