Bedrock river lateral erosion plays a crucial role in landscape evolution, sediment transport and deposition, and the occurrence of geohazards. Fluvial erosion of massive rock is largely driven by impacts of bedload particles, which also drives crack propagation to prepare blocks for plucking. In straight channels, bedload particles generally move parallel to the channel walls and thus need to be deflected laterally to cause wall erosion. Sideward deflection of bedload particles occurs when they interact with roughness elements fixed on the riverbed. Here, we isolated the interaction of moving bedload particles with roughness elements in laboratory experiments. We conducted 21 sets of flume experiments to systematically investigate how spacing (5, 10, 20, 30, 40, 50, and 60 mm) and size (5, 10, and 20 mm) of roughness elements influence sideward deflection of bedload particles in straight channels with relatively low flow depth and a localized roughness zone covering half of the channel width. Velocity changes by the first impact increase with the size of roughness elements. The deflection length and velocity peak at intermediate values of the spacing of roughness elements. The likelihood for a bedload particle to leave the roughness zone decays with the bedload particle's distance to its edge. Our results suggest that lateral erosion rates in bedrock channels are dominantly controlled by the position of the roughness zone within the channel and its relation to the particle path.

中文翻译：

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粗糙度间距和尺寸对底物颗粒横向偏转的影响

基岩河横向侵蚀在景观演化、泥沙输移和沉积以及地质灾害的发生中起着至关重要的作用。大块岩石的河流侵蚀在很大程度上是由床载颗粒的影响驱动的，这也驱动了裂缝扩展以准备开采块。在直通道中，床载颗粒通常平行于通道壁移动，因此需要横向偏转以引起壁侵蚀。当它们与固定在河床上的粗糙元素相互作用时，就会发生河床颗粒的侧向偏转。在这里，我们在实验室实验中隔离了移动床荷载颗粒与粗糙度元素的相互作用。我们进行了 21 组水槽实验，以系统地研究间距（5、10、20、30、40、50 和 60 毫米）和尺寸（5、10、和 20 毫米）的粗糙度元素影响直通道中床载颗粒的侧向偏转，其流动深度相对较低，局部粗糙度区域覆盖通道宽度的一半。第一次冲击引起的速度变化随着粗糙度元素的大小而增加。偏转长度和速度峰值位于粗糙度元素间距的中间值。床载粒子离开粗糙度区域的可能性随着床载粒子到其边缘的距离而衰减。我们的结果表明，基岩通道中的侧向侵蚀速率主要受通道内粗糙区域的位置及其与颗粒路径的关系控制。第一次冲击引起的速度变化随着粗糙度元素的大小而增加。偏转长度和速度峰值位于粗糙度元素间距的中间值。床载粒子离开粗糙度区域的可能性随着床载粒子到其边缘的距离而衰减。我们的结果表明，基岩通道中的侧向侵蚀速率主要受通道内粗糙区域的位置及其与颗粒路径的关系控制。第一次冲击引起的速度变化随着粗糙度元素的大小而增加。偏转长度和速度峰值位于粗糙度元素间距的中间值。床载粒子离开粗糙度区域的可能性随着床载粒子到其边缘的距离而衰减。我们的结果表明，基岩通道中的侧向侵蚀速率主要受通道内粗糙区域的位置及其与颗粒路径的关系控制。