A hybrid investigation of geometrical effects on landslide-tsunamis: Generic hazard assessment and numerical benchmark test cases

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The proposed research concerns the investigation of the effect of the water body geometry on landslide-tsunamis. To predicting such events, at least three approaches may be adopted: (i) physical model testing, (ii) numerical simulations and (iii) empirical equations. Traditionally empirical equations are based on physical model testing. Unfortunately, this model testing has mostly been conducted in narrow wave channels (2D), and did not systematically address the effects of the water body geometry. Numerical simulations of such violent free surface flows have only recently come into practical reach. A promising computational method for solving these problems is Smoothed Particle Hydrodynamics SPH. The proposed work adopts all three methodologies, using physical model testing, to validate and advanced SPH code, and develop the most generic empirical equations to date. The work directly builds upon the PI's previous success in physical landslide-tsunami modelling and real-world applications through his hazard assessment manual.Tsunamis are not only caused by seismic activities such as in the 2011 Japan and 2004 Indian Ocean tsunami catastrophes, but also by other mass movements such as landslides, rock falls or ice calving. Such landslide-tsunamis (or impulse waves in a lake or reservoir) occurred, for instance, off the coast of Norway affecting Scotland in 6100 BC, in the 1963 Vaiont catastrophe with a death toll of about 2,000 or in Papua New Guinea in 1998 with 2,100 fatalities. Impulse waves occur also quite frequently in mountainous countries such as Austria, Canada, China, Italy, Norway, Switzerland and Turkey such that a hazard assessment is required in the planning phase of reservoirs. The UK also experiences similar cases e.g. in Scotland, it may be affected by a potential landslide-tsunami originating at La Palma on the Canary Islands and it is of increased relevance for the shipping and oil and gas industries in the context of ice calving.In contrast to seismic-tsunamis, landslide-tsunamis may be relatively well predicted with empirical equations under idealised conditions. However, these equations were mainly developed in wave channels (2D) and wave basins (idealised 3D) where the wave height predictions with equations based on 2D and idealised 3D differ up to an order of magnitude by identical slide features. At present the differences between 2D and idealised 3D tsunamis generated by identical slide features is poorly understood. It is also not well understood whether formulae based on 2D or idealised 3D data apply better to a specific prototype shape and generic predictions of intermediate geometries (e.g. slide impact at dam flank) are unknown at all. The important effect of the water body geometry was not systematically addressed to date even though it is widely known to be responsible for considerable under- or overestimations in landslide-tsunami (impulse wave) predictions.The proposed work will systematically investigate the effect of the water body geometry with a hybrid (experimental-numerical) approach. The physical model experiments will be conducted in the in-house wave flume and a wave basin thereby excluding significant scale effects. The unique combination of measurements will include the entire slide kinematics, pressure recordings at slide front and wave features. This will result in high quality benchmark test cases valuable for the numerical modelling community dealing with fluid-structure interaction applications and violent free surface flows. The recently released feature to include complex geometries via Blender in SPHysics will make it possible to conduct additional tests in 2D, idealised 3D and intermediate geometries purely numerically. The data set from this hybrid approach will be used to develop the most generic empirical equation to predict landslide-tsunamis (impulse waves) to date resulting in considerably improved predictions in lakes, reservoirs, fiords and the sea.