Landslide risk assessment in coastal settings – Recognizing the challenges and uncertainty

Coastal hazards present a common threat to many Australians given the extensive utilisation of our vast coastal margins. These hazards can take the form of cliff collapse, rockfalls, landslides, karstic features and coastline regression and involve the interface between these terrestrial processes and coastal agents of change including wave action, tidal surge and storm events.

This paper looks at the challenges faced by practitioners and managing authorities when managing public safety on the coast through the undertaking of landslide risk assessments. We look at the adaptation of standard risk assessment approaches to the coastal environment and discuss the use of geomorphic analysis to assist in the determination of key inputs into the risk assessment process. In particular, we review the role of process rates and coastal regression to inform likelihood determination through geomorphic analysis of past coastal erosional environments and the role of sea level and climate variations. Whilst the concepts and approaches discussed in this paper could be applied to many coastal settings and scenarios, this paper considers risk assessment as applied to landslide hazards in coastal conditions with focus on below cliff / beach level users and does not deal with cliff top infrastructure.

The nature of landslide hazards, techniques for assessing likelihood, consequence and the estimation of landslide risk is discussed in the context of coastal settings. We also highlight the challenges faced in delineating the patterns of use by the public, the varying potential for impact within different hazard zones and the complications associated with risk mitigation.