Laboratory Experiments on Breaching Characteristics of Natural Dams on Sloping Beds

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.

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