Laboratory Experiments on Breaching Characteristics of Natural Dams on Sloping Beds

Abstract

Natural dams formed by landslides may produce disastrous floods after dam outburst. However, studies on the breaching characteristics of natural dams on sloping beds systematically are still at an early stage, and especially the relationship between breach width and depth is still unclear. In this paper, results of a series of laboratory tests that assessed seven different flume bed slope angles are presented. The results show that 3 stages of breaching process of natural dams on different bed slopes were observed. According to the results, headward erosion was the main force for enlargement of breach when bed slope was relatively small. With the increasing of bed slope, the effect of tractive erosion on longitudinal development of breach wass enhanced. The discharge hydrographs were unimodal for all the bed slopes. The peak discharge increased first and then decreased with the increasing of bed slope. The elapsed time from the start of breach formation to the moment of peak discharge decreased with the increasing of bed slope. The difference between different bed slopes was larger when the bed slope was small or large, and the relationship between duration and bed slope had the same characteristics. With the increasing of bed slope, the ratio of breach width to breach depth rose to 1 and then decreased with the increasing of bed slope angle. A result of the present work is a function of the relationship between the breach width and depth for which it is possible to calculate them. This function is based on a shape parameter that linearly decreases with bed slope. The relationship between shape parameter and bed slope was developed to calculate the shape parameter with an additional relationship between shape parameter and mean diameter of particles. Combined with the experimental data and filed data of Tangjiashan natural dam, the shape parameter was calculated, and the function was validated.

Numerical Simulation on the Longitudinal Breach Process of Landslide Dams Using an Improved Coupled DEM-CFD Method

“…Model experiments in the laboratory and field are currently the most common approaches for investigating the breach process of landslide dams. Many researchers carried out a series of experiments to explore the breach process of landslide dams under different geomorphological conditions, hydrodynamic conditions and dam geometries mainly focusing on the breach flow discharge, evolution of breach morphology, and erosion characteristics (Davies et al, 2007;Cao et al, 2011;Chen et al, 2015;Xiangang et al, 2018;Wang et al, 2018;Jiang, 2019;Zhou et al, 2019). The breach mechanism of landslide dams was discussed based on macroscopic observation, and the primary factors affecting the landslide dam breach process were identified (such as inflow discharge, barrier lake volume, dam material and downstream slope angle).…”

The formation and geometry characteristics of boulder bars due to outburst floods triggered by overtopped landslide dam failure

“…Above all, there is a common academic consensus that outburst flow triggered by landslide dam failure could change the geomorphology of the downstream riverbed. Although the failure process of the dam and the hydraulic character-istics of the outburst flood, such the characteristics of the breaching hydraulic graph, erosion rate, and peak discharge (Morris et al, 2009;Jiang and Wei 2018;Jiang, 2019), are clear, the impact of the outburst flood triggered by landslide dam failure on the geomorphology of the downstream riverbed during the failure process and after failure is still lacking research. A boulder bar is the substance that occurs during the dam failure process which is an indicator of the variation of riverbed geomorphology.…”