source: production/pt_hedland_2006/report/computational_setup.tex @ 3330

To initiate the modelling, the computational mesh is constructed to
cover the available data. The resolution is chosen to balance
computational time and desired resolution in areas of interest,
particularly in the interface between the on and offshore. he
following figure illustrates the data extent for the 
scenario and where further mesh refinement has been made. The choice
of the refinement is based around the important inter-tidal zones and
other important features such as islands and rivers.
The resultant computational mesh is then seen in \ref{fig:mesh_onslow}
which has an area of around ? km$^2$.
In contrast to the Onslow study, the most northern
boundary of the study area is placed approximately around the 50m contour
line. The driver for this change was the computational time taken to 
develop the mesh and associate the points to that mesh. By comparison, the 
100m contour for the Onslow study is approximately 100km from the coast, 
with that distance approximately 200km for Pt Hedland. The increased
study area (from 6300 km$^2 for Onslow to 24400 km$^2 for Pt Hedland) 
then increases the number of triangles, thereby increasing
the computational time. It would be possible to increase the cell resolution 
to minimise the number of triangles, however, the cell resolution would have
to be raised to an unacceptable level. 
However, initial comparisons between the deep water model MOST (Method of
Splitting Tsunami) and ANUGA show that they are reasonably well matched
to the 50m contour line. More detailed investigations are necessary to 
confirm this position as the point may be dependent on the local bathymetry.

\begin{figure}[hbt]

  \centerline{ \includegraphics[width=100mm, height=75mm]
             {../report_figures/pt_hedland_data_poly.png}}

  \caption{Study area for Pt Hedland scenario}
  \label{fig:pthedland_area}
\end{figure}


\begin{figure}[hbt]

  %\centerline{ \includegraphics[width=100mm, height=75mm]{}}

  \caption{Computational mesh for Pt Hedland study area}
  \label{fig:meshpthedland}
\end{figure}

For the simulations, we have chosen a resolution of 500 m$^2$ for the 
region surrounding the Pt Hedland town centre. The resolution is increased 
to 2500 m$^2$ for the region surrounding the coast and further increased
to 100000 m$^2$ for the region reaching approximately the 50m contour line.
With these resolutions in place, the study area consists of ? triangles. 
The associated accuracy 
for these resolutions is approximatly 22m, 50m, and 315m for the increasing
resolutions. This means
that we can only be confident in the calculated inundation to approximately
22m accuracy within the Pt Hedland town centre. 
This is because ANUGA calculates whether each cell in the triangular
mesh is wet or dry. It is important
to refine the mesh to be commensurate with the underlying data especially in 
those regions where complex behaviour will occur, such as the inter-tidal
zone and estuaries. 

Whilst friction has been incorporated into the model, we have not
implemented it here. 
We have an outstanding issue with regard how friction is
modelled which is not yet resolved.