Slope hazard assessment on a coast road in New South Wales, Australia

Lawrence Hargrave Drive was constructed in 1878 and has experienced a continuance of slope failures including rock falls, debris flows and embankment collapses. In 2003 a section of the road was closed for safety reasons. An Alliance between the state government and private industry was formed to develop an engineering solution to reduce the risk to ‘acceptable’ levels. Assessment of slope hazards was completed with the aid of geological mapping, interpretation of aerial photographs, archived government reports, historical photo and newspaper collections and a GIS based landslide inventory. Historical photographs provided important evidence on erosion rates and the size, nature and frequency of landslide events. A landslide process rate model was developed for the site bringing together knowledge and judgments about erosion rates for the differing materials and landforms on the escarpment. Process rate curves were developed for slope units and integrated into a quantitative risk assessment.