Uniomni

Name: Ole Nielsen Affiliation: Geoscience Australia Position: Senior Computational Scientist

Professional interests:

As computational scientist I have introduced a new modelling capability which has enabled us to simulate impacts of tsunami or storm surge disasters on the built environment and to present the results in forms that are easily interpreted. The software developed is a hydrodynamic modelling tool which is able to predict what consequences a hydrological disaster may have on a particular community.

ANUGA Hydro
A simple example modelled with ANUGA.
Developer(s)	Geoscience Australia and the Australian National University

ANUGA Hydro is a free and open source software tool for hydrodynamic modelling, suitable for predicting the consequences of hydrological disasters such as riverine flooding, storm surges and tsunamis. For example ANUGA can be used to create predicted inundation maps based on hypothetical tsunami or flood scenarios. The ANUGA name without qualification is used informally to mean the ANUGA Hydro tool.

ANUGA

Background

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 have developed a, freely available, hydrodynamic inundation modelling tool called ANUGA to help simulate the impact of these hazards.

Simulation Engine

The fluid dynamics in ANUGA are 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 ANUGA 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. ANUGA is also capable of modelling hydraulic jumps due to the ability of the finite-volume method to accommodate discontinuities in the solution .

User Interface

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 Python numpy structures.

To set up a model of a 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 rainfall, water abstraction, wind stress or atmospheric pressure gradients. Gravity and Frictional resistance from the different terrains in the model are represented by predefined forcing terms.

ANUGA viewer

The ANUGA Viewer is a graphical 3D rendering program suitable for animating the output files from ANUGA.

• 
  The ANUGA viewer showing a simulated flood

Limitations

Although a powerful and flexible tool for hydrodynamic modelling, ANUGA has a number of limitations that any potential user needs to be aware of. They are:

• The mathematical model is the 2D shallow water wave equation. As such it cannot resolve vertical convection and consequently not breaking waves or 3D turbulence (e.g. vorticity).
• All spatial coordinates are assumed to be UTM (meters). As such, ANUGA is unsuitable for modelling flows in areas larger than one UTM zone (6 degrees wide).
• Fluid is assumed to be inviscid – i.e. no kinematic viscosity included.
• The finite volume is a very robust and flexible numerical technique, but it is not the fastest method around. If the geometry is sufficiently simple and if there is no need for wetting or drying, a Finite difference method may be able to solve the problem faster than ANUGA .
• Frictional resistance is implemented using Manning’s formula, but ANUGA has not yet been fully validated in regard to bottom roughness.

Who uses ANUGA

• Geoscience Australia
• Australian National University
• Fire and Emergency Services of Western Australia

What has ANUGA been used for

• ANUGA was trialled as a conventional hydrodynamic 2D flood model on both a complex urban system and a simpler rural system. The urban model included a dam break scenario with flood water passing through a residential area

The model was found to have:

"The ability to construct a model with elements varying in size to suit the features being modelled permitted flow behaviour to be simulated realistically and at a level of local detail that structured grid models cannot practically reproduce"

• ANUGA has been used to asses the likely difference in tsunami amplification and dissipation between different characteristic coastal embayments, coastal entrances and estuaries The results showed that:

"for large embayments, the wave run-up can be amplified by a factor six in comparison to the amplitude at the model boundary. For small embayments, the amplification is dependent on the location of the ocean water line, or tidal stage"

Awards

ANUGA has been used to understand tsunami risk to the Western Australia coastline and the results of this work are being utilised by emergency managers and the Department for Planning and Infrastructure in Western Australia. In 2007 this work received the Asia-Pacific Spatial Excellence Award and the Emergency Management Australia Safer Communities Award.

External Links

ANUGA - Trac - This site contains download links, current news and other related media.

License:

ANUGA is freely available and distributed under the terms of the GNU General Public Licence.