source: production/onslow_2006/report/interpretation.tex @ 3158

The main features of the
tsunami wave and resultant impact ashore is described in this section. 
To assist this description, we have
chosen a number of locations which we believe would be important
in an emergency situation, such as the hospital and power station, or
effect recovery efforts, such as 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 are shown
as a function of time in the series of graphs shown in
Section \ref{sec:timeseries}. Stage is defined as the absolute
water height and is the water depth above the point's elevation.
The graphs show these time series for
the three cases; 1.5 AHD, 0 AHD and -1.5 AHD so that comparisons can
be made. To ease these comparisons, the graphs are shown on consistent
scales and speeds under 0.001 m/s are not shown.
As a useful benchmark, Table \ref{table:speedexamples}
describes typical examples for a range of velocities found in the 
simulations. 

\begin{table}
\label{table:speedexamples}
\caption{Examples of a range of velocities.}
\begin{center}
\begin{tabular}{|l|l|}\hline
Velocity (m/s) & Example \\ \hline
1 & leisurely stroll pace\\ \hline
1.5 & average walking pace \\ \hline
2 & 100m Olympic male freestyle \\ \hline
3 & mackeral \\ \hline
4 & average person maintain for 1000m \\ \hline
5 & blue whale \\ \hline
10 & 100m Olympic male sprinter \\ \hline
16 & car travelling in urban zones (60 km/hr) \\ \hline
\end{tabular}
\end{center}
\end{table}


Examining the offshore locations, the drawdown prior to the tsunami wave 
arriving at the shore can be seen to occur around 230 mins  
(3.8 hours) after the tsunami is generated. 
Prior to the drawdown, maximum amplitudes are approximately 50cm at 
West of Groyne and the mouth of Beadon Creek, for example. The first wave 
after the drawdown ranges from approximatly 2m in the 
west of Beadon Bay to 1.5m in the east of Beadon Bay. The speed 
sharply increases at drawdown with further increases as the 
wave grows in amplitude. 
There is an increased amplitude of approximately 3m found in 
east of Beadon Bay for the secondary wave, as opposed to the first wave. 
This feature is also evident at the West of Groyne location. 
This may be due to the geography of the bay, including the groyne west of 
the creek mouth opening, the local bathymetry
and the direction of the tsunami wave. 

The maximum speed found for the offshore locations occur at the West of 
Groyne location with speeds halved at the Beadon Bay west location. 
The Beadon Bay west speed is greater that the east of Beadon 
Bay location. There is similar differences in amplitude (from drawdown to maximum 
amplitude), however, the western location is in deeper water than the eastern 
location which may indicate the increased speed found in the east of the 
bay.  

Subsequent drawdowns are seen as the multitude of waves which make up the 
event propagate towards the shore. 

%At some gauge locations, these 
%subsequent waves cause significantly increased inundation than that of 
%the first wave. This is particularly seen at the Beadon Creek Docks, 
%West of Groyne and Beadon Creek locations.

It is evident for each simulation that the sand dunes west of 
Onslow are very effective in halting the tsunami wave,
see Figures \ref{fig:MSL_max_inundation} and
\ref{fig:LAT_max_inundation} and  \ref{fig:HAT_max_inundation}. 
The height of these
sand dunes are approximately 10m which is more than enough to halt
the largest of the tsunami waves which occurs for the
1.5 AHD simulation. There is inundation between the sand dunes at high 
tide, Figure \ref{fig:HAT_max_inundation}, however, this water 
penetrated from the north east (via
Onslow town centre) rather than seaward.
The same feature is evident for the sand dunes east of Onslow which
rise to 15m in height. 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. 

The wave penetrates the river east of Onslow with increasingly
greater inundation between the -1.5 AHD and 1.5 AHD simulations.

As expected, there is greater inundation at 1.5 AHD. The major road
into Onslow, the Onslow Mount Stuart Rd, remains free of inundation for
all simulations. Beadon Creek Rd which services the wharf in the
river becomes increasingly inundated as the initial condition
changes from 0 AHD to 1.5 AHD. Only the
entry to the wharf on Beadon Creek Rd is sufficiently inundated at -1.5 AHD
to stop traffic. At 1.5 AHD however, essentially the entire road 
would be impassable.

There is significant inundation of at
least 2m on the foreshore of Onslow for 0 AHD and 1.5 AHD.
The inundation extent increases the initial condition increases above 0 AHD, 
pushing the edges
of the majority of the road infrastructure in the Onslow town centre.