The modelling of muddy debris flows - From laboratory validation to hazard zoning in the field

Abstract

Mudflows are fast, transitory flows formed of a mixture of water and solids with widely varying particle sizes, which occur in certain wet conditions affecting the natural soil. When there is a sufficiently high clay content, the material is, from a macroscopic point of view, thixotropic. The transitory nature of these events required the development of specific numerical models in order to study and predict their behaviour. Two models based on shallow-water equations in conjunction with a special flow model were implemented to represent channelled flows and the spreading of material outside the main channel. These two models were validated in the laboratory by comparison with flows of model fluids (on a reduced scale). The paper then considers the practical application of these models in the field for zoning flood risks. Given the uncertainty of the extent of such events, a study based on flood scenarios was necessary. This approach called for the use of these two models in conjunction with various laboratory or field techniques, which were intended to provide better characterisation of the material liable to flow. This project also reveals directions for research to improve the performance of the tools proposed.