A two-layer model for simulating landslide dam over mobile river beds

Abstract

Landslides can block mountainous streams and form landslide dams to threaten downstream residents. It is necessary for reliable methods to predict landslide dam dynamic for risk assessment. In this paper, we present a two-layer model of SavageHutter type to simulate the dynamic evolution of landslide dam which take account of the erosion of river bed. The two-layer shallow water system is derived by depth-averaging the incompressible Navier-Stokes equations with the hydrostatic assumption integrated of the erosion model of river bed. The effect of excess pore water pressure is considered in the erosion process. A high order accuracy scheme based on Roe-type solver is used to discretize the present model. Finally, several numerical tests are performed to verify the stability of the algorithm and reliability of the model. Numerical results indicate that the erosion effect enhances the huge destructiveness of landslide and increase the possibility of river blocked by landslides. The impact of excess pore water pressure on erosion process should be considered.

Barrier lake formation due to landslide impacting a river: A numerical study using a double layer-averaged two-phase flow model

“…First, existing double layer-averaged models [22,[41][42][43] are based on a single-phase flow premise, in which the water-sediment mixture in the lower flow layer are regarded as a single-phase flow. Therefore, the velocities of the sediment phases in the lower flow layer are assumed to be equal to the mixture velocity.…”

“…Second, existing double layer-averaged models [22,[41][42][43] are confined to single-sized sediment transport (i.e., the sediment size is kept at a single value, normally the median or mean sediment diameter, throughout the simulation). Clearly, the models that assume a single sediment size do not reflect the nature of landslides, which are typically characterized by broad grain size distributions.…”

“…Consequently, they cannot model the deposition process of landslide materials, which is vital to barrier lake formation. Note that the double layer-averaged model by Liu and He [42] incorporated the mass exchange with the bed. However, an additional term, which denotes a real (rather than apparent) momentum exchange with the bed, was incorrectly added into the momentum conservation equations.…”

“…The consequence of this extra term can be serious. For example, according to Liu and He [42], the riverbed is eroded by subaqueous landslide instead of being deposited, which is questionable from physical intuition. Arguably, this is why this model has not yet been validated by any observed data.…”

“…Furthermore, most double layer-averaged models [41][42][43] are based on the assumption of a constant sediment concentration in the lower water-sediment mixture flow layer. However, sediment concentration generally varies in time and space.…”