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