Numerical Experiments on Effect of Topographical Slope Changes in the Dynamics of Landslide Generated Water Waves and Submarine Mass Flows

Abstract

When gravitational mass flows hit water bodies, they create water waves, called tsunami. The slopes of the mountain flanks surrounding a glacial lake or the slopes of the side walls of artificially constructed reservoirs play important roles in the intensity of splash on landslide impact, amplitudes and propagation speeds of the resulting water waves and possible dam breaching or overspilling of water. The proper analyses of such dynamics are useful for the possible mitigation measures. Here, we apply a general two-phase mass flow model to perform several numerical experiments and present geometrically three-dimensional, high-resolution simulation results for rapidly moving two-phase landslide/debris flow down a plane with varying slopes at its different parts, impacting a fluid reservoir. First, the upstream slope is kept constant; later to make it closer to reality, sudden changes in slopes are imposed one after another at different parts of the topography. The results focus on the effects of the sudden slope changes in the formation and propagation of dynamically different solid- and fluid wave-structures in the reservoir. Results show that steeper upper part of the topography produces more highly intensified tsunami that propagates more longitudinally than the steeper lower part. Thus, steeper upper parts need stronger right coast and steeper lower parts demand stronger side walls in mountain reservoirs to withstand the wave impacts. The results may help for the proper modeling of landslide and debris induced mountain tsunamis in rapidly changing slopes, the dynamics of turbidity currents and sediment transports in fluid reservoirs in high mountain slopes.