Modeling of natural dam failure modes and downstream riverbed morphological changes with different dam materials in a flume test

Landslide dam failure modes are influenced by dam geometry, material characteristics, and riverbed conditions. The different characteristics of earthquake- and rainfall-induced natural dams and the effects of riverbed conditions on dam failure have not attracted much attention from researchers in the past. This study used flume tests to simulate earthquake- and rainfall-induced landslide dam failures for various combinations of dam geometry, materials, and riverbed conditions. The 64 flume test combinations thus included two discharge rates, two dam shapes (triangular and trapezoidal) with two heights, two types of riverbed conditions, and two types of dam material with two different water contents. The experimental results show that dam geometry, the amount of inflow, hydraulic conductivity of the dam material, and riverbed conditions have considerable effect on dams' lifespan and their corresponding failure mode. The hydraulic conductivity of the dam material affected the dam lifespan and its corresponding failure mode. The four observed failure modes of dam breaks in rigid and mobile riverbeds constitute progressive erosion, overtopping erosion, slope slide, and complex failure. The complex failure mode, which involves headward erosion, slope slide, and overtopping, can occur in highly hydraulically conductive dams with high discharge. Progressive erosion occurs in highly hydraulically conductive dams with low discharge. Dam material with low hydraulic conductivity tends to fail by pure overtopping. Regardless of the dam shape and material, dams in a mobile riverbed had a longer lifespan than those in a rigid riverbed. The composition of the dam material affected the peak outflow discharge after dam break. Compared with rigid riverbeds, dams in mobile riverbeds delay the arrival time of peak sediment discharge. Failure modes triggering flash floods and sediment transport after a dam break involved a series of sandbars and an armoring layer in the downstream riverbed. Earthquake-induced dry material forming highly hydraulically conductive dams generally fail through complex when failure was subjected to a high discharge. Dams composed of wet materials tend to fail by overtopping. In flume tests, dam failure mode and inflow changed downstream mobile riverbed morphology in ways similar to those seen in full-scale model tests conducted in the field.