Hydrodynamic modelling of coastal inundation

Modelling the effects on the built environment of natural hazards such as riverine flooding, storm surges and tsunami is critical for understanding their economic and social impact on our urban communities. Geoscience Australia and the Australian National University are developing a hydrodynamic inundation modelling tool called AnuGA to help simulate the impact of these hazards. The core of AnuGA is the fluid dynamics module, called pyvolution, which is based on a finite-volume method for solving the shallow water wave equation. The study area is represented by a mesh of triangular cells. By solving the governing equation within each cell, water depth and horizontal momentum are tracked over time. A major capability of pyvolution is that it can model the process of wetting and drying as water enters and leaves an area. This means that it is suitable for simulating water flow onto a beach or dry land and around structures such as buildings. Pyvolution is also capable of modelling hydraulic jumps due to the ability of the finite-volume method to accommodate discontinuities in the solution. To set up a particular scenario the user specifies the geometry (bathymetry and topography), the initial water level, boundary conditions such as tide, and any forcing terms that may drive the system such as wind stress or atmospheric pressure gradients. Frictional resistance from the different terrains in the model is represented by predefined forcing terms. A mesh generator, called pmesh, allows the user to set up the geometry of the problem interactively and to identify boundary segments and regions using symbolic tags. These tags may then be used to set the actual boundary conditions and attributes for different regions (e.g. the Manning friction coefficient) for each simulation. Most AnuGA components are written in the object-oriented programming language Python. Software written in Python can be produced quickly and can be readily adapted to changing requirements throughout its lifetime. Computationally intensive components are written for efficiency in C routines working directly with the Numerical Python structures. The animation tool developed for AnuGA is based on OpenSceneGraph, an Open Source Software (OSS) component allowing high level interaction with sophisticated graphics primitives. The inundation model will be released under an OSS license in 2006. This strategy will enable free access to the software and allow the risk research community to use, validate and contribute to the development of AnuGA.