source: anuga_work/production/onslow_2006/report/interpretation.tex @ 4248

The inundation extent calculated at Onslow will be described in this section with
impact assessments following in Section \ref{sec:impact}.
% there will need to be something in here for when doing a range of events for each return period.
Figures \ref{fig:HAT_max_inundation}, \ref{fig:MSL_max_inundation} and 
\ref{fig:LAT_max_inundation} illustrate the maximum inundation extent
for the Mw 9 event occurring at HAT, MSL and LAT respectively. 
As expected, there is greater inundation at HAT with increased
extent. The major road
into Onslow, the Onslow Mount Stuart Rd, remains free of inundation for
all tidal scenarios with a small amount of inundation evident at HAT at
the intersection with Beadon Creek Rd. Beadon Creek Rd services the wharf in the
creek which becomes increasingly inundated as the tide height
increases. The only road sufficiently inundated at LAT is Beadon
Creek Rd near the entry to the wharf. This road during the HAT 
scenario would be impassable as the water depths are consistently
over 1 m with a maximum water depth of around 2 m found close to 
the wharf. 

There is significant inundation of at
least 2 m on the foreshore of Onslow for MSL and HAT.
The inundation extends further as the tidal heights increase.  
At HAT, the inundation reaches the southern boundaries of 
the road infrastructure in the Onslow town centre.  
The airport remains
free of inundation for each tidal scenario. Section \ref{sec:impact}
details the impact estimates to the residential infrastructure.

The geography of the Onslow area has played a role in offering
some protection to the Onslow community. The tsunami wave is 
travelling from the north west of the area. Most of
the inundation along the coast is that which is open to this
direction.  
The sand dunes west of Onslow 
appear to have halted this tsunami wave
(see Figure \ref{fig:MSL_max_inundation}) with limited
inundation found on the town's side of the dunes.
The inundation within the community has occurred due to the
wave reflecting from the beach area west of the creek and
returning towards the Onslow town itself.  
There are also sand dunes east of the creek which have also
halted inundation beyond them. 
Currently, we do not model changes 
to the bathymetry or topography due to effects of the water flow. 
Therefore, we do not know whether these sand dunes would withstand the
transmitted energy of the tsunami wave. 
Water features such as rivers, creeks and estuaries also play a role
in the inundation extent.
The tsunami wave penetrates the creek east of Onslow, however it
is evident that the inundation is essentailly maintained in the
large tidal flat region surrounding the southern parts of the creek.

In addition to describing the maximum inundation extent,
we have
chosen a number of locations to illustrate the features
of the tsunami as it approaches and impacts Onslow.
These locations have been chosen as we believe they would 
either be critical
in an emergency situation, (e.g. the hospital and power station) or
effect recovery efforts, (e.g. the airport and docks). These locations
are described in Table \ref{table:locations} and shown in 
Figure \ref{fig:points}. The water's stage and speed 
at each of these locations are shown
as a function of time in the series of graphs shown in
Appendix \ref{sec:timeseries}. Discussion of the main features of the
tsunami wave is also described in Appendix \ref{sec:timeseries}.