source: production/onslow_2006/report/discussion.tex @ 3285

%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_dted} 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_dli} 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.

\begin{figure}[hbt]

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

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

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. As
before, 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}.