The Corangamite region in southwest Victoria, Australia is subject to a variety of geohazards, among which landslides and erosion have the most significant impact. Over the past fifty years, landslides have resulted in loss of life and many millions of dollars damage to municipal infrastructure and development. Soil erosion by water and wind has also impacted on the region's waterways and environment, threatening a diverse range of assets from urban water quality to Ramsar-listed wetlands. More assets are placed at risk each year, as the increasing regional population results in an acceleration of anthropogenic modifications to landscapes. A comprehensive GIS database was initiated by assembling all publicly available previous databases and reports documenting landslides and erosion in the 1,340 km2 region. New data were added by mapping occurrences which were visible on high-resolution ortho-corrected aerial photographs. The field-checking of the occurrences was assisted by the participation of the local community, municipal officers and catchment management coordinators. At present 2163 landslides and 2380 erosion sites have been identified, mapped and referenced in the database. It is believed that thousands more instances exist, but these cannot be identified at the aerial photo scale, or are obscured by dense vegetation. A spatial analysis has been undertaken to identify landscape parameters which correlate with the occurrences. Historical aerial photography was used in selected locations to identify the rates of erosion and landslide events. The inventory has been used to estimate the economic, social and environmental costs of landslides and soil erosion within the region, using documented instances of damage and the costs of remediation. Combined with the value of the assets and elements at risk, the potential likelihood of occurrence and associated consequences, these estimates are used to develop a strategy for the investment of public funds in remediation.
The Corangamite region covers an area of approximately 13,340 km2 and is located in south western Victoria, Australia. The population of approximately 400,000 persons is growing at 5.2% per year, and is served by nine municipalities within the region. The region's diverse range of landscapes and climatic conditions, result in a variety of geological hazards including landslides, soil erosion of all forms, coastal erosion, dryland salinity, potential acid sulphate soils, reactive soils and ground subsidence. These geohazards are increasingly recognised as a constraint on future urban development and a threat to the economic, social and environmental health of the region. Evaluation of the impacts of geological hazards by State government authorities, research institutions and consultants has been inconsistent, both in hazard identification and risk assessment methods. As a result, municipal planning authorities have lacked a consistent framework with which to assess the potential impacts from these hazards and those associated with new developments which may interact with the hazards. The use of risk assessment techniques for the management of landslides in Australia advanced significantly after the publication of the Australian Geomechanics Society's landslide risk management concepts and guidelines in 2000. These guidelines in turn were based on the Australian/New Zealand Standard on Risk Management. Similar risk management techniques have now been developed by the authors for the assessment of soil erosion and salinity for particular use by municipalities within the Corangamite region. A brief review of the nature and extent of landslides, salinity and erosion in the Corangamite region is detailed. The adopted methods of the risk management for each geohazard are described including a comparison of their applicability and an assessment of limitations with each method.