
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. Onslow is termed a Standard Port
by the Australian Hydrographic Service, with tidal
predictions based on continuous observation of the tide
over a period of at least one year, however it is advised that these
observations extend to three years to note changes in the mean
sea level. The Australian National Tide Tables 2006 \cite{antt:06}
describes how
these predictions are rounded to two decimal places, then
further rounded to a single decimal place. 
Figure \ref{fig:contours} shows the contour lines for
the values for
Highest Astronomical Tide (HAT; 1.5m AHD), Mean Sea Level (MSL; 0m AHD) 
and Lowest Astronomical Tide (LAT; -1.5m AHD) for Onslow, \cite{antt:06}.
It is evident from this figure that the extent of the tidal
inundation is exaggerated. This is due to
short comings with the digital elevation model which has been 
derived from 20m contour lines. {\bf Need some words from hamish here.}

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.

\begin{figure}[hbt]

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

  \caption{Onslow regions showing the 1.5m AHD, 0m AHD and -1.5m AHD contour lines.}
  \label{fig:contours}
\end{figure}