source: production/onslow_2006/report/anuga.tex @ 3174

The software tool, ANUGA \cite{ON:modsim}, has been used to develop 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.
An advantage of this technique is that the cell area 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.
As such, the current results represent ongoing work
and may change in the future.

The following set of 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 condition (the tsunami source as described in 
Section \ref{sec:tsunamiscenario})
\item forcing terms (such as wind)
\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. However, throughout the modelling process, a number of issues became
evident. A standard assumption is that zero Australian Height Datum
(AHD) is approximately 
the same as Mean Sea Level (MSL). Implementing the values provided for
Highest Astronomical Tide (HAT) and Lowest Astronomical Tide (LAT)
would inundate some regions of Onslow before the simulation is even begun.
Further, the recorded value for HAT will not be identical at each 
point along the coastline. There
is evidence suggesting different high tide marks (with respect
to a set datum) within
a localised region. As an aside, a current GA contract is
extracting information from LANDSAT imagery to reconstruct the 
tidal variations for various WA locations. Future modelling of
these areas will incorporate this information.
Further, the dynamics of
tidal effects (that is, the changes in water height over time for
the entire study area) is not currently modelled.
In the simulations provided in this report, we assume that 
increase of water height for the initial condition is spatially consistent
for the study region. 

We use three initial conditions in this report;
-1.5m AHD, 0m AHD and 1.5m AHD. Figure \ref{fig:ic} shows the Onslow region
with the 1.5m AHD and -1.5m AHD contour lines shown. It is evident then
that much of Onslow would be inundated at a uniform tide at 1.5m AHD.
Bottom friction will generally provide resistance to the water flow
and thus reduce the impact somewhat. However, it is an open area
of research on how to determine the friction coefficients, and 
thus it has not been incorporated
in the scenarios presented in this report. Therefore, the 
results presented are over estimated to some degree.

\begin{figure}[hbt]

  \centerline{ \includegraphics[width=150mm, height=100mm]
{../report_figures/contours.jpg}}

  \caption{Onslow regions showing the 1.5m AHD and -1.5m AHD contour lines.}
  \label{fig:ic}
\end{figure}