CAS Key Laboratory of Mountain Hazards and Surface Process, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences (CAS), Chengdu 610041, China; University of Chinese Academy of Sciences, Beijing 100039, China.
CAS Key Laboratory of Mountain Hazards and Surface Process, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences (CAS), Chengdu 610041, China; China-Pakistan Joint Research Center on Earth Sciences, Islamabad 30001, Pakistan; University of Chinese Academy of Sciences, Beijing 100039, China.
Sci Total Environ. 2022 Dec 10;851(Pt 2):158378. doi: 10.1016/j.scitotenv.2022.158378. Epub 2022 Aug 28.
Outburst floods related to glacial or landslide damming are a major agent of geomorphic change in mountain rivers. Although the evidence between outburst flooding and riverine landscapes has been gradually recognized, the lack of hydraulics to the extent that there has still not been quantified on the relationship of how the amount and spatial distribution of these changes relate quantitatively to the hydraulic conditions and durations of these catastrophic events. This study combined remote and field observations of the 2018 Baige outburst flood with two-dimensional numerical simulation using the diffusive wave equation. By feeding the measured dam-breach hydrograph and comparing three different Manning coefficients in numerical experiments, the simulation results show that when n = 0.055, the time of peak flow was only 0.5 h different from that indicated by measured data in Yebatan, 54 km downstream of the Baige landslide dam. Under high shear stress over several hours at sustained ~20 m water depth, lateral erosion caused by these outburst floods contributed to the adjacent landslide, which was activated in association with intermittent water velocity waves of approximately 17 m/s. Sustained high stream power (>50 kW m) from the outburst flood eroded slope toes and accelerated slippage of six slopes. Combining simulation and observations, we also developed a physical model related to hillslope instability caused by high hydrodynamic erosion of riverbanks generated by flow waves lasting several hours, which explained the hydrodynamic response of the outburst flood to the canyon geomorphology. Furthermore, we suggest that the pattern of channel widening erosion and deposition is governed by the variation in shear stress and Froude number as the high-energy flood flows from a wide channel into a narrow river valley. Our findings highlight that the hydraulics of high-magnitude outburst floods and sediment transport play crucial roles in reshaping canyon geomorphology.
爆发洪水与冰川或滑坡堵塞有关，是山区河流地貌变化的主要因素。尽管爆发洪水与河流地貌之间的证据逐渐得到认可，但由于缺乏水力学方面的研究，尚未对这些变化的数量和空间分布与这些灾难性事件的水力条件和持续时间之间的关系进行量化。本研究结合了 2018 年白玉爆发洪水的遥感和现场观测，以及使用扩散波方程的二维数值模拟。通过输入实测坝决口流量过程线，并在数值实验中比较三种不同的曼宁系数，模拟结果表明，当 n = 0.055 时，峰值流量出现的时间仅比 54 公里下游的野三滩实测数据晚 0.5 小时。在几个小时的高剪切应力作用下，持续约 20 米水深，这些爆发洪水造成的侧向侵蚀导致相邻滑坡体被激活，并与间歇性约 17 米/秒的水流波有关。持续的高水流功率（>50kW m）从爆发洪水中侵蚀了边坡趾部，并加速了六个边坡的滑移。结合模拟和观测，我们还开发了一个与河岸高动水侵蚀引起的山坡失稳有关的物理模型，该模型解释了持续数小时的水流波对峡谷地貌的爆发洪水动力响应。此外，我们认为，河道扩宽侵蚀和沉积的模式是由剪切应力和弗劳德数的变化控制的，当高能量洪水从宽河道流入狭窄的河谷时，这两种力都会发生变化。我们的研究结果强调了高量级爆发洪水的水力学和输沙作用在塑造峡谷地貌方面的重要作用。
