source: production/onslow_2006/report/damage.tex @ 3339

%This section deals with impact modelling which covers damage
%modelling and economic impact analysis.
In this report, impact modelling refers to damage as a result
of the inundation described in Section \ref{sec:results}. This damage
is reported as damage to infrastructure as well as
number of human injuries and is determined assuming
that the event occurs at night. The infrastructure
refers to residential structures only and is sourced from the 
the National Building Exposure Database (NBED). The NBED has been
created by Geoscience Australia so that consistent risk assessments for a range
of natural hazards can be 
conducted\footnote{http://www.ga.gov.au/urban/projects/ramp/NBED.jsp}. 
It contains information
about residential buildings, people, infrastructure, 
structure value and building contents.
From this database, we find that there
are 325 residential structures and a population of approximately 770
in Onslow\footnote{Population is determined by census data and an ABS 
housing survey}. 


To develop building damage and casuality estimates, we briefly describe 
residential collapse probability models and casualty models and their 
application to inundation modelling. There is limited data found in
the international literature to support the development of
vulnerability models. However,
with reported observations made of building performance during the 
recent Indian Ocean tsunami, vulnerability models have been proposed for 
framed residential construction. The models predict the collapse 
probability for an exposed population and incorporate the following 
parameters known to influence building damage \cite{papathoma:vulnerability},

\begin{itemize}
\item   inundation depth at building    
\item   building row from coast 
\item   building material (residential framed construction)     
\item   inundation depth at house above floor level
\end{itemize}   

The collapse vulnerability models used are presented in Table \ref{table:collapse}. 
In applying the model all structures in the inundation zone were 
spatially located and the local water depth and building row 
number from the exposed edge of the suburb were determined for each.

Casualty models were developed by making reference to the 
storm surge models used for the Cairns Cyclone Scenario and 
through consultation with Dr David Cooper of NSW Health, \cite{cooper:2005}. 
The injury probabilities for exposed populations were selected 
based on the nocturnal nature of the event, the collapse outcome 
for the structure, the water depth with respect to 
sleeping height (1.0 m) and the limited warning noise for people 
in the first three city blocks (six house rows) that could potentially 
awaken them. The three injury categories correspond with the 
categories presented in HAZUS-MH \cite{NIBS:2003} for earthquake 
related injury. The casualty model used is presented in Table
\ref{table:casualty} 
and the injury categories are presented in Table \ref{table:injury}. 
Input data comprised of resident population data at census
district level derived from the ABS 2001 census.

The damage to the residential structures in the Onslow community
is summarised in Table \ref{table:damageoutput}. The percentage
of repair cost to structural value shown is based on the total structural value
of \$60,187,955. Likewise, the percentage of contents loss shown is
based on the total contents value of \$85,410,060 for
the Onslow region. The injuries sustained is summarised
in Table \ref{table:injuries} with around \% affected in the 0m AHD 
scenario. 
Around \%
of the population are affected in the 1.5m AHD scenario with around \%
affected in the 0m AHD scenario.


\begin{table}[h]
\begin{center}
\caption{Residential damage sustained for the MSL, HAT and LAT scenarios.}
\label{table:damageoutput}
\begin{tabular}{|l|l|l|l|l|l|l|}\hline
&Houses  & Houses  & Structural & Repair Cost \% & Contents & Contents Loss \% \\ 
&Inundated & Collapsed & Repair Cost 
& of Total Value & Losses & of Total Value \\ \hline
MSL & & 1 & \$ &   \% & \$ &  \% \\ \hline
HAT & & & & & & \\ \hline
LAT & & & & & & \\ \hline
\end{tabular}
\end{center}
\end{table}

\begin{table}[h]
\begin{center}
\caption{Injuries sustained for the MSL, HAT and LAT scenarios.}
\label{table:injuries}
\begin{tabular}{|l|l|l|l|l|l|}\hline
&Minor & Moderate & Serious & Fatal \\ \hline
MSL & &  &  & \\ \hline
HAT & & & & \\ \hline
LAT & & & & \\ \hline
\end{tabular}
\end{center}
\end{table}

Impact on indigeneous communities are important considerations when determining
tsunami impact, especially as a number of communities exist in coastal regions.
These communities are typically not included in national residential databases 
and would be therefore overlooked in damage model estimates.
There is one indigeneous community located in this study area as seen
in Figure
\ref{fig:points}. The population of the Bindibindi community is 140 
(18 \% of the Onslow population)
and is situated close to the coast as seen in Figure \ref{fig:points}.
During the HAT scenario, 
over 1m of water will inundate parts of the community (Figure 
\ref{fig:gaugeBindiBindiCommunity}) causing significant damage.