Modelling the Impact of Tropical Cyclone Larry Infrastructure Damage
On 20 March 2006 at 7am, Cyclone Larry crossed the tropical north Queensland coast near Innisfail (Figure 1). While there were no fatalities, Cyclone Larry caused extensive wind related damage to infrastructure. Electricity transmission was cut around Innisfail and the power disruption affected essential services and utilities such as the hospital, water supply and water treatment works. Road and rail access to the region was also disrupted for several days from heavy rain and severe flooding.
Geoscience Australia's involvement
Geoscience Australia was involved in a multifaceted response to the event.
- Provided 2 500 maps of the affected area for Department of Defence emergency-response personnel following the initial impact
- Worked with James Cook University, TimberEd Services and the Australian Building Codes Board to assess the structural damage to residential and commercial buildings and infrastructure.
Within 48 hours, post disaster survey teams were dispatched to assess structural damage to residential and commercial buildings and infrastructure. Survey teams recorded building and property information such as construction type, building materials, number of floors, and damage sustained.
The building survey indicated that among residential properties, pre-1986 homes tended to suffer the greatest wind damage due to:
- their vulnerable locations such as on ridge tops
- building regulations that required limited cyclone-resistance measures at the time of construction
- their lower resilience due to aging processes such as corrosion and insect attack.
In addition to engineering considerations, the impact of local winds on structures was significantly influenced by:
- geographical terrain
- structure height
- shielding by upwind structures
- topographical factors.
It was found that structures built after Cyclone Winifred hit Innisfail in 1986, withstood Cyclone Larry better, and damages were relatively minor. This may be due to the revised building standards introduced for domestic construction in the early 1980s and a better understanding of prevention methods (Figure 2).
For older structures the overall damage losses were within the range 10-15 per cent of full reconstruction costs, while for structures built following the introduction of the new building regulations (incorporating information learned from Cyclones Tracy in 1974 and Althea in 1971), the damage losses were about 5 per cent.
Geoscience Australia used computational modelling to predict the local wind hazard of Cyclone Larry and then compared the results of modelling to the findings of the extensive post-disaster damage survey.
How can this be used?
The assessment of structural damage contributes to a better understanding of extreme cyclonic wind gusts and provides engineers with highly detailed data on the vulnerability to severe wind of houses and other structures. When this is combined with information from similar events and other sources, it provides a better understanding of severe-wind risk to Australian communities. This knowledge helps Australian communities in preparing for future cyclone events and reduces their potential impact.
- Bureau of Meteorology (2006), Severe Tropical Cyclone Larry.
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