Dynamics of Debris Flow: Reproducible Initial and Boundary Conditions in Scaled Laboratory Experiments to Determine Velocity Distributions
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Debris flows are rapid flows of water, sediments and debris, which can pose a danger to life and infrastructure. Reducing the risk by implementing protections and countermeasures requires a comprehensive understanding of the overall process. Therefore, the task of experts is the prediction of the occurrence probability, frequency, magnitude, flow paths, forces and velocities of debris flows as well as their associated destruction potential. The estimation of velocity distributions and shear stresses is particularly important, as they have an impact on the propagation of debris flow as well as erosion rates, which remain largely unknown by now. Yet, no measuring devices feasible to measure bed shear stresses and basal velocities of debris flows exist. The aim of our investigation is hence to experimentally analyze velocity profiles and shear stresses of granular debris flows with variable but reproducible boundary conditions. To meet the requirements, we built up a 4 m long, 0.3 m wide and 0.3 m high flume in the laboratory. The flume is hinged in the middle, working like a rocker, which enables experimental runs to either side of the flume. It is the first model with this particular feature, which enables the repeated use of the same material for a series of tests at comparable initial conditions. Within preliminary tests we focused on the determination of surface flow velocities. In different experimental scenarios we varied the channel inclination and solids content. As measurement instruments we used ultrasonic probes and Large-Scale Particle Image Velocimetry (LSPIV). The measurements show the velocity distribution and level heights of the debris flows. The results for the different scenarios lead to a better process understanding. Thereby, they will serve as basis for the determination of shear stresses and the development of a numerical model, which we plan. The combination of both models is of central importance for the development of protection and countermeasures.