Impact force characteristics of outburst flows triggered by dam breach: Insights from flume experiments

Outburst floods triggered by dam failures are highly destructive, and their impact-force characteristics constitute a key indicator for hazard risk assessment and engineering mitigation. A comprehensive understanding of these characteristics is essential for revealing dam-breach processes and the dynamic evolution of outburst flows. In this study, we systematically investigate the impact-force characteristics of outburst floods through a series of flume experiments conducted under varying inflow discharges, dam-material grain sizes, and downstream channel-bed conditions. The results show that the impact forces of outburst flow are strongly controlled by the evolution process of the dam breach and exhibit a distinct three-stage evolution, characterized by rapid growth, intense fluctuations, and gradual decay. The impact forces can be separated into a mean component and a fluctuating component. Increasing inflow discharge can enhance both the mean impact forces and the intensity of fluctuating forces, and coarsening of the dam material and downstream bed sediments leads to a marked increase in the proportion of high-frequency energy (>30 Hz) in the impact-force spectra, indicating more intense particle-collision processes. A strong temporal correspondence is observed between impact-force fluctuations and seismic power in the time domain, with both signals effectively capturing particle collisions and interactions within the flow, suggesting that impact-force fluctuations can serve as a reliable proxy for sediment transport intensity. This study not only elucidates the multiscale characteristics and governing mechanisms of impact forces during dam failures, but also provides valuable insights for the engineering mitigation and hazard management of outburst floods.