Abstract: The viscosity of slurry affects the roughness coefficient of debris flow by changing the internal and external resistance characteristics of debris flow. Such influence is often neglected and has not been quantitatively expressed based on observed data. In this paper we explore the relation between roughness coefficient and viscosity of slurry based on field measurement data at the downstream channel of Jiangjia Ravine. By regression fitting we acquire the formula of calculating the roughness coefficient of debris flow in consideration of the viscosity of slurry, and further establish the mathematical relation between velocity of debris flow and viscosity. Results illustrate that the roughness coefficient of debris flow increases with the augment of viscosity of slurry. In other words, the viscosity of slurry enhances resistance in a macroscopic sense. The present formula overcomes the shortcomings of existing formulae in calculating the velocity of debris flow with high viscosity. The results provide a reference for further study of the influence of viscosity of slurry on the resistance of debris flow, and offer a new idea for calculating flow velocity and designing energy dissipation methods.

Key words: debris flow, velocity, viscosity of slurry, Manning's roughness coefficient, Jiangjia Ravine