Tsunami risk modelling for Australia: understanding the impact of data

Abstract

Modelling the impacts from tsunami events is a complex task. A simplification is obtained by taking a hybrid approach where two different models are combined: relatively simple and fast models are used for simulating the tsunami event and the wave propagation through open water. The impact from tsunami inundation is simulated with another type of model which is suitable for resolving the details of the run-up process and the resulting inundation. The inundation modelling is conducted using the ANUGA model which is a result of collaboration between the Australian National University and Geoscience Australia. It solves the 2D nonlinear shallow water wave equations using a finite volume method.

One of the critical requirements for reliable inundation modelling is an accurate model of the earth's surface that extends from the open ocean through the inter-tidal zone into the onshore areas to be studied. Production of a sufficiently accurate elevation model is a complex and difficult process made more difficult because the available elevation data inevitably will come from a number of different sources and will have a range of vintages, resolutions and reliability.

There are two questions that arise when data is requested. The first deals with the true variability of the topography. Obviously, a flat surface needn’t be sampled nearly as finely as a highly convoluted surface. The second question relates to sensitivity; how are error bars derived for the impact results if the error bars on each elevation point is known? ANUGA solves the 2D nonlinear shallow water wave equations using a finite volume method and typical models can take days of computational time, so proper sensitivity analyses are often prohibitively expensive in terms of computational resources.

The main aim of this project was therefore to understand the uncertainties in the outputs of the inundation model based on possible uncertainty in the input data.