Modelling the Effect of Rheological Parameters on Submarine Debris‐Flow Runout Distance and Frontal Velocity

ABSTRACT

Prediction of submarine debris‐flow runout distance and frontal velocity is vital to the siting of seabed structures. The rheological parameters have a great influence on runout distance and frontal velocity, whereas their effect has rarely been quantified. The in‐house developed code MassFlow2D is used to study the influence of rheological parameters on runout distance and frontal velocity. A scenario of debris‐flow motion on a uniform slope is synthesised. Sensitivity analysis is performed to study the influence of skin drag, form drag, and added mass coefficients due to ambient water. Results show that the effect of skin drag coefficient on frontal velocity is striking, whereas that of form drag and added mass coefficients is trivial. Numerical simulations are conducted to investigate the effect of rheological parameters. The yield stress has a major control over runout distance. Both yield stress and dynamic viscosity have a striking impact on frontal velocity. The effect of rheological parameters on runout distance, maximum frontal velocity, and runout length is quantified based on empirical relationships. Comparisons of the empirical prediction of runout distance with experimental, analytical, and numerical results show reasonable agreement. The implication and limitation of this study for the siting of seafloor structures are discussed.