source: production/onslow_2006/report/discussion.tex @ 3339

%As part of the CRA, it was decided to provide results for the
%extremes of the tidal regimes to understand the potential range of impacts 
%from the event. The Highest Astronomical Tide (HAT) and Lowest
%Astronomical Tide (LAT) are defined as 1.5m AHD and -1.5m AHD 
%respectively for Onslow, \cite{antt:06}. These values are tidal
%predictions based on continous tidal observations from Standard Ports
%over a period of
%at least one year, with the Australian Hydrographic Service
%recommending this be extended to three years to capture
%changes to the mean sea level. Onslow is listed as
%a Standard Port. 

%As an aside, current work at GA is
%extracting information from LANDSAT imagery to reconstruct the 
%tidal variations for various WA locations. Future modelling of
%these areas will incorporate this information.

Initial simulations for this study used the DIGO DTED Level 2 data
(see Section \ref{sec:data}) due to the fact it is
``bare earth'', whereas the DLI data is distorted by 
vegetation and buildings.
Figure \ref{fig:contours_compare} shows the contour lines for
HAT, MSL and LAT for Onslow using the DTED data where it is evident 
that the extent of the tidal inundation is exaggerated. This is due to
short comings with the digital elevation model (DEM) created from 
the DTED data. The DEM has been 
derived from 20m contour lines. {\bf Need some words from hamish here.}
As a result, we turned to the WA DLI onshore data to present
the results in this report. Figure \ref{fig:contours_compare} shows
the contour lines for HAT, MSL and LAT for Onslow using the WA DLI data.
It is obvious that there are significant differences in each DEM with
secondary information regarding total station surveys and the knowledge
of the HAT contour line pointing to increased confidence in the WA DLI
data over the DTED data for use in inundation modelling.

The purpose of this section then is to show the differences to the impact
ashore when each data set is used to demonstrate the importance of using the
best possible data set. The maximum inundation map is shown for the MSL 
scenario using the DTED data in 
Figure \ref{fig:MSL_map_DTED} which can be compared with the equivalent map for 
the WA DLI data, Figure \ref{fig:MSL_max_inundation}. Given that the 1.5m contour
line is further from the coast for the DTED data than the DLI data, we
expect to see the inundation to reach further and thus be greater than
that seen in Figure \ref{fig:MSL_max_inundation}. This is confirmed by
Figure \ref{fig:MSL_map_DTED}. These results point to the need for the best 
available data so that more accurate predictions regarding the 
inundation can be made.

Additionally, we show the time history of the water's stage and 
velocity for the point locations in Table \ref{table:locations} for
both the DTED and DLI data at MSL. These results are shown in Section
\ref{sec:timeseriescompare}.
\pagebreak

\begin{figure}[p]

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

 % \caption{Onslow region showing the -1.5m AHD (LAT), 0m AHD (MSL)
 %and -1.5m AHD (LAT) contour lines using the DTED Level 2 data.}
 % \label{fig:contours_dted}
%\end{figure}

%\begin{figure}[hbt]

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

  \caption{Onslow region showing the -1.5m AHD (LAT), 0m AHD (MSL) 
and -1.5m AHD (LAT) contour lines using the DTED Level 2 data and
the WA DLI data.}
 % \label{fig:contours_dli}
 \label{fig:contours_compare}
\end{figure}

\begin{figure}[p]

  \centerline{ \includegraphics[width=\paperwidth]
{../report_figures/mid_tide_DTED.jpg}}

  \caption{Maximum inundation map for the Onslow region using
  the DTED data.}
  \label{fig:MSL_map_DTED}
\end{figure}