Dam-break characteristics of landslide dams with different types of open channel discharge sections

Abstract

The excavation of artificial open channels in landslide dams is one efficient method for reducing the risks of landslide lake formation. This method has often been used in emergencies to eliminate landslide lakes in earthquake-prone areas of Wenchuan, China. In this study, the dam-break characteristics of landslide dams with different open channel cross sections and longitudinal sections were evaluated. The degree of headward erosion was extremely strong in the natural dam-break experiment and moderately strong in the compound-section dam-break experiment. The degree of headward erosion in the open channel with the trapezoidal section was comparatively mild. Furthermore, the natural dam break resulted in large peak discharge and short dam-break duration. By contrast, the artificially opened channel dam breaks resulted in peak discharges that were approximately 7.7-20.1 % lower than those of natural dam breaks, and the dam-break duration (i.e., the time until the dam broke) was longer than that of the natural dam breaking. The channels with gentle-steep slopes or alternating gentle-steep slopes resulted in greater discharge rates, and a significant amount of erosion occurred due to these open channels. The degree of headward erosion in the channel with alternating gentle-steep slopes was greater than that in the other channels. The peak discharges of the open channels with gentle-steep slopes or alternating mild-steep slopes were approximately 29.6-65.0 % greater than those of the open channel with a linear section. A channel with a triangular cross section and a linear longitudinal section should be used to dispose of small landslide lakes. However, channels with compound cross sections and longitudinal sections with alternating slopes should be used for large or medium landslide lakes.