source: production/onslow_2006/report/interpretation.tex @ 3332

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
Appendix \ref{sec:timeseries}. Stage is defined as the absolute
water level relative to AHD. Both stage and speed are shown
on consistent scales to allow comparison between point locations.
%The graphs show these time series for
%the three cases; 1.5m AHD, 0m AHD and -1.5m AHD so that comparisons can
%be made. 
As a useful benchmark, Table \ref{table:speedexamples}
describes typical examples for a range of velocities found in the 
simulations. 

\begin{table}
\begin{center}
\caption{Examples of a range of velocities.}
\label{table:speedexamples}
\begin{tabular}{|l|l|}\hline
{\bf Velocity (m/s)} & {\bf 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 shown in Section \ref{sec:timeseries}, 
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 (Figure \ref{fig:gaugeWestofGroyne}) and 
the mouth of Beadon Creek
(Figure \ref{fig:gaugeBeadonCreekmouth}), for example. 
The first wave 
after the drawdown ranges from approximately 2m in the 
west of Beadon Bay (Figure \ref{fig:gaugeBeadonBaywest})
to over 3m in the mouth of Beadon Creek
(Figure \ref{fig:gaugeBeadonCreekmouth}). 
The speed 
sharply increases at drawdown with further increases as the 
wave grows in amplitude. 
There is an increased amplitude of approximately 4m 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 but
with decreased amplitude. 
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 (Figure \ref{fig:gaugeWestofGroyne}). 
The speeds at west and east of Beadon Bay are quite similar
(Figure \ref{fig:gaugeBeadonBayeast} and Figure \ref{fig:gaugeBeadonBaywest}). 
however, there are increased amplitudes (from drawdown to maximum 
amplitude), in the eastern location which is in shallower water than the western 
location.
Subsequent drawdowns are seen as the multitude of waves which make up the 
event (see Figure \ref{fig:MOSTsolution}) 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 that the sand dunes west of 
Onslow are very effective in halting the tsunami wave,
see Figure \ref{fig:MSL_max_inundation}. 
There is inundation between the western 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 DEM indicates that 
this area is under 1.5m which is automatically deemed to inundated
at HAT.)
The same feature is evident for the sand dunes east of Onslow. 
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 tsunami wave penetrates the river east of Onslow with a wave height 
over 2m at the mouth 
(Figure \ref{fig:gaugeBeadonCreekmouth}) 
and inundation
exceeding 1m found at the Beadon Creek south of dock location (Figure
\ref{fig:gaugeBeadonCreeksouthofdock}).
The wave penetrates the river east of Onslow with increasingly
greater inundation between the -1.5m AHD and 1.5m AHD simulations.

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

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