2025 Volume 81 Issue 16 Article ID: 24-16053
Waterfalls often migrate with formation of upstream cyclic steps. In this study, we hypothesized that the face angle and drop height of waterfall would affect the flow field of upstream channel and alter waterfall migration mechanism. We conducted laboratory experiments with erodible mortar beds to investigate migration rate, flow filed and bedload saltation trajectory from PIV and PTV analyses. Our experimental results suggest that (ⅰ) the face angle changes gradually with erosion, and when the angle exceeds a certain angle, no step is formed upstream, (ⅱ) since the final face angle is determined by the drop height, the final migration rate is dependent on the drop height, (ⅲ) as the face angle becomes steeper, the location of the increase in particle impact velocity moves away from the waterfall lip and the step formation interval increases, (ⅳ) as the drop height increases, the collision frequency decreases due to the increase in saltation distance, making it harder for steps to form.
