source: production/onslow_2006/report/data.tex @ 3390

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1The calculated run-up height and resulting inundation ashore is determined by
2the input topographic and bathymetric elevation, the
3initial and boundary conditions, as well as the cell area of the computational
4mesh.
5Ideally, the data should adequately capture all complex features
6of the underlying bathymetry and topography. Any limitations
7in the resolution and accuracy of the data will introduce
8errors to the inundation maps, in addition to the range of approximations
9made within the model.
10
11In this study, we used the Australian Height Datum (AHD)
12as the vertical datum. Mean Sea Level (MSL) is approximately equal to
130m AHD with the Highest Astronomical Tide (HAT)
14and Lowest Astronomical Tide (LAT) defined as 1.5m AHD
15and -1.5m AHD respectively for Onslow \cite{antt:06}.
16These values are tidal
17predictions based on continous tidal observations from Standard Ports
18over a period of
19at least one year, with the Australian Hydrographic Service
20recommending this be extended to three years to capture
21changes to the mean sea level. Onslow is listed as
22a Standard Port. As an aside, current work at GA is
23extracting information from LANDSAT imagery to reconstruct the
24tidal variations for various WA locations. Future modelling of
25these areas will incorporate this information.
26
27Data for this study have been sourced from a number of agencies. With
28respect to the onshore data, the Defence Imagery and Geospatial
29Organisation (DIGO) supplied the Digital Terrain Elevation
30Data Level 2 (DTED) which has been authorised for Australian Tsunami
31Warning System use only. The resolution of this data is 1 second
32(about 30 metres), and has been produced from 1:50 000 contours, elevations and
33drainage. In addition, the Department of Land Information (DLI) has provided a
3420m Digital Elevation Model (DEM) and orthophotography
35covering the NW Shelf. The DTED Level 2 data is ``bare earth'' while the
36DLI data is distorted by vegetation and buildings. 
37
38Figure \ref{fig:contours_compare}(a) shows the contour lines for
39HAT, MSL and LAT for Onslow using the DTED data where it is evident
40that the extent of the tidal inundation is exaggerated. In particular,
41parts of Onslow town appears to be inundated at HAT before a tsunami has
42even been generated. This is due to
43short comings with the digital elevation model (DEM) created from
44the DTED data.
45Figure \ref{fig:contours_compare}(b) shows
46the contour lines for HAT, MSL and LAT for Onslow using the WA DLI data.
47It is obvious that there are significant differences in each DEM with
48total station survey information and the knowledge
49of the HAT contour line pointing to increased confidence in the WA DLI
50data over the DTED data for use in the inundation modelling.
51The impact difference based on these two onshore data sets
52will be discussed in Section \ref{sec:issues}.
53
54
55\begin{figure}[p]
56\center{(a)}
57  \centerline{ \includegraphics[width=150mm, height=100mm]
58{../report_figures/onslow_dted_contour.jpg}}
59
60 % \caption{Onslow region showing the -1.5m AHD (LAT), 0m AHD (MSL)
61 %and -1.5m AHD (LAT) contour lines using the DTED Level 2 data.}
62 % \label{fig:contours_dted}
63%\end{figure}
64
65%\begin{figure}[hbt]
66\center{(b)}
67  \centerline{ \includegraphics[width=150mm, height=100mm]
68{../report_figures/onslow_dli_contour.jpg}}
69
70  \caption{Onslow region showing the -1.5m AHD (LAT), 0m AHD (MSL)
71and 1.5m AHD (HAT) contour lines using the (a) DTED Level 2 data and
72the (b) WA DLI data.}
73 % \label{fig:contours_dli}
74 \label{fig:contours_compare}
75\end{figure}
76
77With respect to the offshore data, the Department of Planning and
78Infrastructure (DPI) have provided state digital fairsheet data around
79Onslow. This data cover only a very small geographic area. (Note,
80similar data have been provided by DPI for Pt Hedland and Broome.)
81The Australian Hydrographic Office (AHO) has supplied extensive
82fairsheet data which has also been utilised. In contrast to the onshore data, the offshore data is a series of survey points which is typically not supplied on a fixed grid. In addition, offshore data typically does not have the coverage of the onshore data, and often the offshore data will have gaps where surveys have not been conducted.
83The coastline has been generated by
84using the aerial photography, two detailed surveys provided
85by WA DPI and a number of total station surveys of Onslow.
86The WA DLI data surrounding the coast are error prone and
87have been clipped at the derived coastline.
88Appendix \ref{sec:metadata} provides more details and the supporting metadata
89for this study, including images of the data extent.
90Table \ref{table:data} summarises the available data.
91
92\begin{table}
93\caption{Available data for the North West shelf tsunami inundation studies.}
94\label{table:data}
95\begin{center}
96\begin{tabular}{|l|l|}\hline
97Data & Detail \\ \hline 
98DIGO DTED Level 2  & Onshore, 1 second $\approx$ 30m \\ \hline 
99DLI & Onshore, 20m DEM and orthophotography \\ \hline
100DPI & Offshore, fairsheet data around Onslow \\ \hline
101AHO & Offshore, fairsheet data for North West Shelf region \\ \hline
102\end{tabular}
103\end{center}
104\end{table}
105
106
107\pagebreak
108
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