Compressibility of solid phase of debris flow and erosion rate

Abstract

The change in sediment concentration of debris flow causes erosion and sedimentation of the solid phase of debris flows. Moreover, the changing affects the mobility of the flow. Therefore, knowledge of the mechanism of the changing is important to understand the mechanism of debris flow. The changing can be considered as compressibility of the flow of the solid phase. We developed a constitutive equation set of debris flow by concerning energy dissipation. A part of the energy dissipation is due to inelastic collision of particles. This process must be compressible. Therefore, we reinvestigate the process of the inelastic collisions and the effect to the compressibility. As the result, we lead internal energy to control the compressibility and so-called erosion rate equation. According to the erosion rate equation, it depends on bed gradient and energy loss gradient. A flume test is conducted to evaluate the erosion rate equation. by using a prismatic steep slope channel, which inclination is set at 12 degrees. By comparison of experimental result with the erosion rate equation, it is found that the difference between energy gradient and bed gradient to control the erosion/deposition is not so large. It means that the erosion/deposition might be very much sensitive against the unbalance of the energy gradient and bed gradient.