Experimental investigation on the longitudinal evolution of landslide dam breaching and outburst floods

Abstract Accurate prediction of the evolution of a landslide dam that is breached due to overtopping failure is necessary to estimate the outflow hydrograph and the resulting inundation. In this study, physical flume tests on the breaching of landslide dams were conducted. A wide grain size distribution with unconsolidated dam material was used. Dam breaching was initiated by cutting a notch across the crest of the dam adjacent to the side wall of the flume. This allowed water to escape from the dam while a steady inflow of water was continuously supplied upstream. The effects of upstream inflow on the timescales and magnitudes of the peak discharges and the time to inflection point were also investigated. Experimental results reveal that the whole hydrodynamic process of dam breaching can be divided into three stages defined by clear inflection points and peak discharge. A new longitudinal evolution model is proposed. This model captures the initial increase of the soil erosion rate (of landslide dam) and its subsequent decrease along the longitudinal direction. In addition, a linear relationship between the soil erosion rate and shear stress (of water flow) was observed and this is similar to that observed in large-scale natural landslide dams. Furthermore, soil erosion resistances (of landslide dam) against water flow above are observed to increase with the concentration of entrained sediments along the flow direction.