Experimental investigation of breaching process of moraine dam with different breach-section shapes

Moraine dam breaches occur suddenly and have severe consequences. However, breach-process prediction is challenging. Breach-notch excavation is crucial for risk reduction, but no consensus have been reached regarding the optimal notch shape. This study considers the typical characteristic parameters of the Jialongcuo glacial lake and trapezoidal, triangular, and compound notches. In this study, three flume tests were conducted to study the breach-shape impact on the peak discharge and erosion development of the dam during dam-breaching process, while controlling the excavation volume and depth. The compound- and triangular-breach peak discharge values surpass that of the trapezoidal type by 18.4% and 12.2%, respectively. Additionally, the trapezoidal breach exhibits average erosion rates that are > 50% lower, both laterally and vertically, at its initial erosion section, indicating milder erosion and improved outflow efficiency. The results emphasize that the notch-bottom width is critical, and that a trapezoidal notch with equal depths yields higher initial outflow efficiency owing to its greater bottom width. An analysis based on dam erosion process theory agrees with the experimental results and confirms the conclusions. Based on the erosion rates taken from the experiments, a comparison of sediment transport values is given for the three tests. The results indicate that the trapezoidal notch has a relatively small bed load transport. Our work is expected to provide references for the selection of better notch shape.