Science to show impact of Cyclone Debbie

The damage caused by Tropical Cyclone (TC) Debbie in Queensland’s Whitsunday region has been investigated by a team of Bushfire and Natural Hazards CRC researchers. In the lead up to and immediately after TC Debbie, the team of Dr David Henderson, Dr Geoff Boughton, Dr Daniel Smith, Ms Debbie Falck, Mr Mitch Humphries and Mr Korah Parackal of the Cyclone Testing Station at James Cook University, and Thomas Kloetzke of the University of Queensland, set up wind monitors and assessed building damage.

Making landfall on 28 March near Airlie Beach, the investigation of TC Debbie will inform the CRC project Improving the resilience of existing housing to severe wind events. Issues investigated by the team included:

• Performance of contemporary buildings, including wind-driven rain water ingress
• Assessment of older housing
• Storm tide damage to buildings

The team installed six Surface Weather Information Relay and Logging Network (SWIRLnet) towers in the potential path of the cyclone, from Ayr just south of Townsville, through to Proserpine, to measure wind speeds, direction and pressure. The 3.2m tall towers used anemometers to continuously collect data in the affected areas before, during, and after landfall. The highest wind gust recorded by the SWIRLnet towers was 125.7km/h in Bowen.

On 30 March the team headed south to Proserpine and Bowen. In Proserpine they conducted street surveys and observed minor structural damage of contemporary housing, while some older housing and commercial properties suffered damage to sections of roof structure.

It was noted that there was partial separation of roof members, even though no major structural roof damage was initially obvious from the outside. After seeing similar damage, such as battens partially separated from rafters, in investigations following TC Larry (2006) and TC Yasi (2011), the researchers recommend inspections by qualified builders, building surveyors or structural engineers of the inside of the roof structure (of typically older houses), be performed on buildings in areas where structural damage to other buildings has occurred (Bowen, Proserpine and Airlie Beach).

In Airlie Beach the investigation focused on issues relating to water ingress of contemporary housing and strata buildings. The issues identified were primarily associated with windows and doors, though other water paths were noted such as loosened/bent barges, removed flashings and blocked gutters.

Nearby Dingo Beach and Hideaway Bay reportedly experienced the eye of TC Debbie but showed less signs of structural damage. The team spoke to residents who described a two hour lull during the passage of the eye.

“Despite experiencing severe winds during the event, most houses at Dingo Beach and Hideaway Bay had no obvious signs of damage. The majority of houses observed were relatively new, built since 2000,” Dr Henderson noted.

Along the Whitsunday coast at Conway and Wilson Beaches, the team noted wind and storm tide damage to properties. In Wilson Beach water levels and wave action saw one older house lifted off its piers. Water levels throughout houses varied from less than 300 mm to 1100 mm.

“Residents who remained during the cyclone reported that the rising sea water came from over the beach dune and from the mangroves and channel to the rear of community,” Dr Henderson explained.

With the absence of substantial wave action on most properties, the structural damage was minimal. However inundation damaged most of the linings, cabinetry and wiring.

Hamilton Island, along with the other Whitsunday Islands, bore the brunt of TC Debbie. Tree and vegetation damage appeared to be much worse across the island than at Airlie Beach and Proserpine.

“Structural issues with window fixings and frames were observed in some of the buildings on Hamilton Island,” explained Dr Henderson.

Issues ranged from window reveals not being secured to the building frame, minimal capacity lintels not able to resist lateral wind pressures, and sliding doors bowing out of tracks. Examples of wind-driven rain entering buildings were also observed.

“Several modern buildings at Hamilton Island and on the mainland had roof overhangs or awnings that had failed at the structural supports and then peeled back over the building causing more damage.”

Further damage to larger buildings was reported, including the airport, multi-storey apartments, apartments under construction and newer houses in locations exposed to the south east.

The Cyclone Testing Station and University of Queensland team has prepared a preliminary report based on SWIRLnet observations and a media-based damage assessment, available at http://bit.ly/TC_Debbie.

The team will continue working on the data they have collected to prepare a formal report.

The CTS has a series of videos for both homeowners and builders to provide some information on repairing damaged roofs from cyclones. These videos can be found at www.youtube.com/user/cyclonesandbuildings/videos