source: production/pt_hedland_2006/report/anuga.tex @ 3373

The software tool, ANUGA \cite{ON:modsim}, has been used to estimate 
the inundation extent
and associated water level at various points in space and time.
ANUGA has been developed by GA and the Australian National University
(ANU) to solve the nonlinear shallow water
wave equation using the finite volume technique\footnote{The finite volume
technique belongs to the class of computational fluid dynamic (CFD)
methods which is based on discretizing the study area in
control ''volumes''. The method satisfices conservation
of mass, momentum and energy and is exactly satisfied for
each control volume.
An advantage of this technique is that the discretization
can be changed
according to areas of interest and that wetting and drying
is treated robustly as part of the numerical scheme.}. 
ANUGA is continually being developed and validated to ensure
the modelling approximations reflect new theory or
available experimental data sets.
As such, the current results are preliminary.

The following information is required to undertake the 
inundation modelling;

\begin{itemize}
\item onshore and offshore elevation data (topographic and bathymetric data, 
see Section \ref{sec:data}),
\item initial conditions, such as initial water levels (e.g. determined by tides),
\item boundary conditions (the tsunami source as described in 
Section \ref{sec:tsunamiscenario}), and
\item computational requirements relating to the mesh construction.
\end{itemize}

As part of the CRA, it was decided to provide results for the
extremes of the tidal regimes to understand the potential range of impacts 
from the event. In this study, we used the Australian Height Datum (AHD)
as the vertical datum. Mean Sea Level (MSL) is approximately equal to
0m AHD with the Highest Astronomical Tide (HAT) 
and Lowest Astronomical Tide (LAT) defined as 3.6m AHD
and -3.9m AHD respectively for Onslow, \cite{antt:06}. 
These values are tidal
predictions based on continous tidal observations from Standard Ports
over a period of
at least one year, with the Australian Hydrographic Service
recommending this be extended to three years to capture
changes to the mean sea level. Onslow is listed as
a Standard Port. As an aside, current work at GA is
extracting information from LANDSAT imagery to reconstruct the 
tidal variations for various WA locations. Future modelling of
these areas will incorporate this information.

The initial conditions used for this scenario are MSL, HAT and LAT.
The dynamics of
tidal effects (that is, the changes in water height over time for
the entire study area) are not currently modelled.
Sea floor friction will generally provide resistance to the water flow
and thus reduce the impact somewhat. However, limited
research has been carried out to determine 
the friction coefficients, and 
thus it has not been incorporated
in the scenario presented in this report. The 
results are therefore likely to be over estimations.