Quantitative Landslide Hazard Assessment in an Urban Area

Before decisions can be made concerning the management of sloping areas subject to landsliding, systematic approaches for hazard and risk assessment must be developed. This paper is limited to a discussion of hazard assessment and describes quantitative approaches which have been developed for existing landslides. Consideration of areas of potential landsliding is outside the scope of the paper. The approach described here is based on (a) monitoring of subsurface shear movement at instrumented sites and (b) the percentage exceedance time of cumulative rainfalls considering different selected periods of antecedent rainfall. This approach is used in conjunction with a simpler approach, described in a previous paper, which is based on the historical frequency of landsliding. Numerical values of hazard thus calculated enable a ranking of all landslides to be made in descending order of hazard levels. The approach has been validated in the particular study area considered in this paper, ie, the northern suburbs of the City of Wollongong.