Real-scale Smoothed Particle Hydrodynamics Tsunami Runup Modelling, with application to 3-D tsunami urban flows in Cilacap, South Java, Indonesia

The risk posed by tsunami waves is currently modelled over bare-earth representations by tsunami models. The complex flows around buildings and structures are crucial to represent the true state of the tsunami wave elevation, speed and forces exerted on buildings. Such 3D simulations have been unachievable for real scale modelling at a reasonable computational cost. We present here for the first time the use of Smoothed Particle Hydrodynamics (SPH) for tsunami simulation in a real setting of large scale (around 1 km). Our illustration is for Cilacap, Indonesia as constitutes a blueprint for future scenarios in South Java. SPH allows for the efficient modelling of shocks and complex interations of the flows with the structures. We also offer a range of test cases of increasing complexity and realism to tune and validate such realistic simulations, including the well known simplified beach of Seaside, Oregon at scale 1:50. We are able to reproduce realistic wave heights, velocities and even observed eddies. We provide guidance and discuss the various choices in terms of flow parametrisations, boundary conditions, and the trade-off of fidelity. computational cost. As a result, Probabilistic Tsunami Risk Assessments (PTRA) will become possible by making use a of combination of regional modelling of tsunamis with depth-average models (generation and propagation) as well as coastal modelling using SPH.