Investigation on the breach mechanism of ice-containing blockage dams: Insights into the impact of ice melting on overtopping erosion

Abstract

With global climate warming, ice avalanches have become increasingly frequent, often resulting in the formation of blocked dams. The presence of ice complicates the failure processes of these dams. Limited observations of breach processes and insufficient consideration of ice as a dam component impede the understanding of these processes. In this paper, a series of flume experiments were carried out to examine the effects of ice melting on overtopping breach mechanisms in dams. The results demonstrate that higher ice content enhances dam settlement and porosity, reducing structural stability. Dam height decreases from 30 cm (ice-free) to 18.5 cm at 60 % ice content, while void ratio increases from 0.82 to 1.73. These changes accelerate overtopping onset and reduce water storage capacity. The breach process can be divided into three stages: backward erosion, accelerated erosion, and attenuation-rebalancing. Both the duration of each stage and the total breach time decrease with increasing ice content. Peak discharge surges by 48.1 % (from 5.2 L/s to 7.7 L/s) at 30 % ice content and occurs 26.7 % earlier (from 172 s to 126 s). Beyond 30 % ice content, reduced water storage suppresses peak discharge (4.3 L/s at 60 % ice content). Ice melting creates new flow paths and enlarges pores in the dam, accelerating fine sediment transport and increasing dam heterogeneity. It also enhances erodibility index (from 0.0157 to 0.0516 cm·Pa⁻¹·s⁻¹) and reduces the critical shear stress (from 20.5 to 8.2 Pa) of dam materials. The ice phase modulates overtopping erosion process by controlling the erodibility of the dam materials and shear stress exerted by water flow. According to the ice content, three modes of erosion dynamics are revealed: enhanced amplification mode, attenuated amplification mode, and inhibitory breach mode. This study sheds light on the combined effects of internal ice melting and scour erosion in dams, providing valuable scientific insights for disaster prevention in glacial regions and paving the way for further research on the role of ice in dam breaches.