Quantitative Landslide Risk Assessment of Cairns

A GIS-based quantitative landslide risk assessment was carried out in the Cairns area to provide information to the Cairns City Council on landslide hazard, community vulnerability and risks for planning and emergency management purposes. Magnitude recurrence relations were tentatively established for the two main slope processes: landslides on the hill slopes and large debris flows extending out from the gully systems on to the plains. From the recurrence relations, landslide hazard (H) was estimated as the annual probability of a point being impacted by a landslide. The nature, number (E) and geographic distribution of the elements at risk were obtained by interrogating the GIS, and their vulnerabilities (V) to destruction by the two main landslide slope processes were assessed. From this information, specific risk (= HxV) and total risk (= HxVxE) maps were produced. Landslide risk may increase as development extends further into the hill slopes. Large debris flows could impact on subdivisions at the base of the slopes. Blockage by landslides of roads and railways could cause isolation of the community. Flash flooding in Freshwater Creek, or debris flows, have the potential to disrupt the Cairns water supply by blocking the intake or destroying sections of the pipeline.