source: production/onslow_2006/report/interpretation.tex @ 3005

%\clearpage
The following subsections detail the time series at the locations
described in the previous table
%table \ref{table:gaugelocations}
for Highest Astronomical Tide (HAT), Lowest Astronomical Tide (LAT) and 
Mean Sea Level (MSL) conditions. These locations 
have been chosen to assist in describing the features of the tsunami wave
and the resultant impact ashore. Here, we assume that MSL coincides with 
AHD zero. This is a standard assumption and confirmed with the WA DPI.
The graph ranges for both stage and 
velocity are made consistent for each of comparison. In addition, velocities 
under 0.001 m/s are not shown. As a useful benchmark, the following table 
describes typical examples for a range of velocities found in the 
simulations. 

\begin{table}
\label{table:speed_examples}
\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}

In simulating different tidal conditions, we assume that the 
tidal conditions are the same for all locations in the study region. 
It is worth noting here that ANUGA does not model tidal effects (that is, 
the change in water height over time). To incorporate this effect in 
a consistent way would also involve having information about the 
difference in tide heights for every location in the region. This 
information is not available on a national scale, 
therefore our approach of applying a uniform change in water 
height is a reasonable one. 

The Australian Hydrographic Office fair sheet for Onslow describes the 
chart datum to be LAT with MSL and HAT being 1.5 and 3 respectively. This 
then places HAT and LAT at 1.5 AHD and -1.5 AHD respectively. Other 
detail on the chart describes the blah de blah mark to be MHWS.

Hamish/Kathryn - does the Onslow coastline coincide with the yellow bit on the 
Onslow map? If so, does that place AHD 0 at MHWS? 

It is evident from figure \ref{fig:ic_high} 
that much of Onslow would be inundated at Highest Astronomical Tide (HAT) 
(1.5m above MSL).
HAT is the projected tide on a 19 year cycle (occurring when a number of
astronomical conditions happen simultaneously), and Mean High Water Springs 
(MHWS) is the tide which is projected to occur ... (get the words
from the ANTT 06). The 
Australian National Tidal Tables 2006 determines MHWS for Onslow to be 1m 
(adjusted to AHD) which also places regions within the study area under 
water before a tsunami wave reaches the shore. Using HAT or even 
MHWS in this way has significant infrastructure inundated which does not 
seem reasonable. Therefore, we show results for MSL only and 
provide a 
qualitative discussion on the changes to the inundation at HAT and LAT.  

\begin{figure}[hbt]

  %\centerline{ \includegraphics[width=100mm, height=75mm]{../report_figures/.png}}

  \caption{Initial condition for mean sea level.}
  \label{fig:ic_zero}
\end{figure}

\begin{figure}[hbt]

  %\centerline{ \includegraphics[width=100mm, height=75mm]{../report_figures/.png}}

  \caption{Initial condition for lowest astronomical tide.}
  \label{fig:ic_low}
\end{figure}

\begin{figure}[hbt]

  %\centerline{ \includegraphics[width=100mm, height=75mm]{../report_figures/.png}}

  \caption{Initial condition for highest astronomical tide.}
  \label{fig:ic_high}
\end{figure}

Examining the offshore gauges, 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 velocity 
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 velocity found for the offshore gauges occurs at the West of 
Groyne location with velocities halved at the Beadon Bay west location. 
The Beadon Bay west velocity is greater that the gauge in the east of Beadon 
Bay. There is similar differences in amplitude (from drawdown to maximum 
amplitude), however, the west gauge is in deeper water than the east 
gauge which may indicate the increased velocity 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.

({\bf Note, these words are assuming that the current simulations are OK,
and will have to be updated once we have more information about
the tides etc}).
It is evident for each simulation that the sand dunes west of 
Onslow are very effective in halting the tsunami wave. 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
high tide simulation. There is inundation between the sand dunes at high 
tide, however, this water penetrated from the north east (via
Onslow town cetnre) rather than seaward.
The same feature is evident for the sand dunes east of Onslow which
rise to 15m in height. Currently, ANUGA can 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 as the tide changes from LAT to HAT.

As expected, there is greater inundation at high tide. The major road
into Onslow, the Onslow Mount Stuart Rd, remains free of inundation for
all tidal scenarios. Beadon Creek Rd which services the wharf in the
river becomes increasingly inundated as the tide rises. Only the
entry to the wharf on Beadon Creek Rd is sufficiently inundated at LAT
to stop traffic. At HAT however, essentially the entire road 
would be impassable.

There is significant inundation of at
least 2m on the foreshore of Onslow for MSL and HAT.
The inundation extent increases as the tide rises, pushing the edges
of the majority of the road infrastructure in the Onslow town centre.