source: anuga_work/production/dampier_2006/report/anuga_setup.tex @ 4479

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1The following information is required to undertake the
2inundation modelling;
3
4\begin{itemize}
5\item onshore and offshore elevation data (topographic and bathymetric data,
6see Section \ref{sec:data}),
7\item initial conditions, such as initial water levels (e.g. determined by tides),
8\item boundary conditions (the tsunami source as described in
9Section \ref{sec:methodology}), and
10\item computational requirements relating to the mesh construction.
11\end{itemize}
12 
13Here, we choose HAT as the only initial condition for this study
14as we expect a greater impact to occur. HAT is
15defined in Section \ref{sec:data}.
16The dynamics of
17tidal effects (that is, the changes in water height over time for
18the entire study area) are not currently modelled.
19
20To set up a model for the tsunami scenario, a study area is first
21determined. Here, we define the study area to
22extend offshore to around the 70m depth contour with the onshore data covering the
23area of interest to CIPMA. The study area is around 6250 km$^2$.
24
25The finite volume technique relies on the construction of a triangular mesh which covers the study region.
26This mesh can be altered to suit the needs of the scenario in question. The mesh can be refined in areas of
27interest, particularly in the coastal region where complex behaviour is likely to occur. For the purpose
28of this study for CIPMA, we will refine the mesh around the major onshore gas facility and the gas pipelines.
29In setting up the model, the user defines the area of the triangular cells in each region of interest\footnote{Note that the cell
30area will be the maximum cell area within the defined region and that each
31cell in the region does not necessarily have the same area.}.
32Figure \ref{fig:dampier_area} shows the study area with regions of difference cell areas. The total number
33of cells is 177 191.
34Lateral accuracy refers to the distance at which we are confident in stating a region is inundated.
35Figure \ref{fig:dampier_area} shows the maximum triangular cell area and lateral accuracy for each region.
36Therefore we can only be confident in the calculated inundation extent surrounding the onshore
37gas infrastructure to within 30 m.
38
39
40\begin{figure}[hbt]
41
42  \centerline{ \includegraphics[scale=0.5]{../report_figures/dampier_model.jpg}}
43
44  \caption{Study area for Dampier scenario highlighting four regions of increased refinement.
45Region 1: Surrounds onshore gas infrastructure at Dampier with a cell area of 500 m$^2$ (lateral accuracy 30 m) - not shown here.
46Region 2: Surrounds the gas pipelines with a cell area of 2000 m$^2$ (lateral accuracy 100 m).
47Region 3: Surrounds the coastal regions with a cell area of 10000 m$^2$ (lateral accuracy  m).
48Region 4: The remaining area is given a cell area of 100000 m$^2$ (lateral accuracy 450 m).
49}
50  \label{fig:dampier_area}
51\end{figure}
52
53
54The final item to be addressed to complete the model setup is the
55definition of the boundary condition. As
56discussed in Section \ref{sec:methodology}, a Mw 9 event provides
57the tsunami source. The resultant tsunami wave is made up of a series
58of waves with different amplitudes which is affected by the energy
59and style of the event as well as the bathymetry whilst it travels
60from its source to Dampier. The amplitude and velocity of each of these
61waves are then provided to ANUGA as boundary conditions and propagated
62inshore.
63
64Sea floor friction will generally provide resistance to the water flow
65and thus reduce the impact somewhat. However, limited
66research has been carried out to determine
67the friction coefficients, and
68thus it has not been incorporated
69in the scenario. The
70results are therefore likely to be over estimates.
71
72The following table summarises the modelling parameters;
73
74
75\begin{table}
76\begin{center}
77\caption{Parameters used in ANUGA for the Dampier scenario.}
78\begin{tabular}{|l|l|l|}\hline
79Mesh & & \\ \hline
80& resolution in Region 1 & 500 m$^2$  \\ \hline
81& resolution in Region 2 & 2000 m$^2$ \\ \hline
82& resolution in Region 3 & 2000 m$^2$ \\ \hline
83& remaining resolution & 100 000 m$^2$ \\ \hline
84Model parameters & & \\ \hline
85& friction & 0 \\ \hline
86& minimum stored height & 0.1 m \\ \hline
87\end{tabular}
88\end{center}
89\end{table}
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