Numerical investigation of flash flood dynamics due to cascading failures of natural landslide dams

Abstract

A series of natural landslide dams commonly form in a river valley in mountainous areas. Their failures are frequently triggered by intense rainfall, which may result in severe flash flooding or debris flow in a short period. It is important for risk mitigation to develop greater evidence-based understanding of flood dynamics due to cascading dam failures. Based on detailed hydro-morphodynamic modeling of various scenarios, this study systematically evaluates the formation and evolution of flash floods due to a cascading failure of natural landslide dams. The hydro-morphodynamic model has been shown to be capable of simulating shock-captured flows and resultant morphological changes. In this study, we first calibrate the dynamic model with dedicated experimental data, and then apply it to simulate a variety of designed flash flood scenarios caused by cascading dam failures. Moreover, process-based flood dynamics and their evolution are explored in detail. Results indicate that cascading dam failures in a sloping channel cause an overall amplification of flash flood dynamics in the flow direction, but fluctuation of key hydraulic parameters occurs around each dam. Also, bigger landslide dams prevent upstream flood propagation better, but the blockage of the flows raises the potential flow energy. This implies a higher potential hazard risk in case of ‘sudden-onset’ failure of the dam. Moreover, the shape characteristic of a channel (straight or with bends) influences the evolution of the flash flood along the sloping channel. The findings enhance the understanding of the formation and evolution mechanisms of flash floods due to cascading failures of natural landslide dams, and hence are beneficial for assessing hazard risk and developing mitigation strategies for flash flooding in mountainous areas.