source: production/onslow_2006/report/anuga.tex @ 3158

The software tool, ANUGA \cite{ON:modsim}, has been used to develop the 
inundation extent
and associated water height 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 tsunami
inundation modelling;

\begin{itemize}
\item onshore and offshore elevation data (topographic and bathymetric data, 
see Section \ref{sec:data})
\item initial condition (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 definition of a mesh parameter values
\end{itemize}

As part of the CRA, it was decided to provide results for the
ends of the tidal regimes to understand the potential impact of the 
event. Throughout the modelling process, a number of issues became
evident. A standard assumption is that zero 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 enough 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 consistently
for the study region. 

We use three initial conditions in this report;
-1.5 AHD, 0 AHD and 1.5 AHD. Figure \ref{fig:ic} shows the Onslow region
with the 1.5 AHD and -1.5 AHD contour lines shown. It is evident then
that much of Onslow would be inundated at 1.5 AHD.


\begin{figure}[hbt]

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

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


It is important
to refine the model areas to be commensurate with the underlying data especially in 
those regions where complex behaviour will occur, such as the inter-tidal
zone and estuaries. In modelling the tsunami wave in deep water, 
it is suggested that the minimum model resolution
be such so that there are at least
ten cells per wavelength. The modelling
undertaken to develop the preliminary hazard map \cite{BC:FESA}
used a 
grid resolution which can adequately model tsunamis with a
wavelength of 50km. Bottom friction has not been incorporated
in the scenarios presented in this report. It 
can be accommodated in ANUGA as a forcing term, however, it is an
open area of research on how to determine the friction coefficients. 
Therefore, the results presented are overly compensated to some degree.