Establishing a Methodology for Coastal Cliff Hazard Mapping: An East Coast Bays, Auckland Pilot Study

In this study, efforts have focussed on developing a coastal cliff hazard map for East Coast Bays shorelines, extending from Milford to the Okura Estuary within North Shore City, Auckland. Three pilot areas have been identified as having different sets of cliff variables such as cliff- face aspect, height, angle, lithology, faults, and joint spacing, to name a few, that influence cliff stability. In this paper, we firstly outline the overall methodology to determine Coastal Landslide Hazard Zone (CLHZ) for North Shore City and then apply this methodology to one of the sites, J.F. Kennedy Memorial Park. Here, CLHZ is calculated to range in width from 23 m to 52 m inland from the cliff- toe. The width is proportionate to the degree of risk within the next century from coastal erosion and landslip. CLHZ's are ultimately intended to be used by Regional and District authorities as a tool for future planning to control subdivision, use, and development along cliff coastlines. We also anticipate that the correlation between each cliff variable and overall composite relationship to coastal instability and/or cliff-top recession can be modelled. Provided that detailed information of key variables exist for a defined area, we will be able to apply the Weights of Evidence spatial model to predict cliff instability, and potentially assign CLHZ along other Auckland Region shorelines.