First steps towards a national assessment of Australian wind risk  

Authors / CoAuthors

Nadimpalli, K. | Edwards, M. | Cechet, R.P. | Driessen, M. | Forghani, A.

Abstract

In August 2002 the Council of Australian Governments (COAG) published a review of natural disaster relief and mitigation arrangements in Australia (COAG, 2003). One of the recommendations from this review included a commitment by COAG to develop and implement a five-year national program of systematic and rigorous disaster risk assessments. In response to this commitment, Geoscience Australia has undertaken a series of national risk assessments for a range of natural hazards including severe wind. This study includes four case studies representing different wind regions Perth (Region A), Brisbane (Region B), Gold Coast (Region B) and Cairns (Region C) to estimate the wind risk. Severe wind is one of the major natural hazards in Australia. These severe winds are chiefly produced by cyclones in the north and cold fronts or thunderstorms in the south. Geoscience Australia has developed a national wind hazard model for estimating the risk posed by peak wind gusts. In this study, the regional return period wind gusts used were as defined in the Australian/New Zealand wind loading standard (AS/NZS 1170.2, 2002) and applied the methodology detailed in the standard. The impact of severe wind varies considerably between structures at various locations, due to the geographic terrain, the height of the structure concerned, the surrounding structures and topographic factors. The wind multipliers defined in the AS/NZS 1170.2 can numerically describe the site wind exposure and speed modifications. These multipliers give quantitative measures of local wind conditions relative to the regional wind speed (defined as open terrain at 10 metre height) at each location. There are three local wind multipliers named terrain/height multiplier (Mz), shielding multiplier (Ms) and topographic (also called hill-shape) multiplier (Mh) influence the regional wind speed. The developed model estimates these multipliers using remote sensing and spatial information. The directional multiplier (Md) is considered from the standards determines the wind direction The relationship between the regional wind speed (VR) in open terrain at 10 metre height, the maximum local (site) wind speed (Vsite) and the local wind multipliers is: Vsite = VR × Md ×Mz × Ms × Mh The wind loading standard is known to be conservative in its approach to shielding by buildings upwind in a "shielding zone", and also with regard to the topographic shielding of structures. A number of modifications were made to remove the conservatism associated with AS/NZS 1170.2. The link between incident wind speed and loss is the structural vulnerability and contents loss model. For this study the models developed by George Walker for North Queensland structures using insurance loss data form two cyclone events have been used after validation. Damage levels across each region were assessed for various return periods (50-, 100-, 200-, 500-, 1000-, 2000- year). Severe wind damage losses were determined for each return period hazard level. Each city data set was regressed to obtain a corresponding Probable Maximum Loss (PML) curve. Finally the regression curves were used to determine annualised losses for each study area. The annualised percentage losses were estimated for Perth (0.0039), Brisbane (0.021), Gold Coast (0.04) and Cairns (0.137). In addition, spatially variable regional wind speeds for Perth region were estimated using eight weather stations data and linear interpolation techniques. The wind damage estimated using these wind speeds is significantly higher than the estimated from single station based wind speeds of AS/NZS 1170.2.

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nonGeographicDataset

eCat Id

64107

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• GA PublicationRecord

( Theme )

• risk assessment

( Theme )

• model

( Theme )

• wind

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

Publication Date

2006-01-01T00:00:00

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geoscientificInformation

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