This paper documents a novel procedure for assessing the vulnerability of an open-coast dune system to tsunami hazard. Geographic Information System (GIS)–based analyses of Light Detection and Ranging (LIDAR) data are employed to classify a range of dune topographies in terms of four tsunami inundation scenarios, run-up to 3, 6, 8, and 10 m above mean sea level, along the coast of Christchurch, New Zealand.

Analysis reveals two key characteristics which together define the tsunami vulnerability of a narrow vegetated dune system: (i) the elevation or average height of the dune ridge and (ii) the continuity or standard deviation of height of its longshore profile. We find that the Christchurch dune coast currently offers a high degree of protection against inundation from small to medium tsunami (run-up ≤6 m above mean sea level), with the degree of vulnerability under more extreme scenarios varying longshore in relation to the height and continuity of the dune system and its vegetation.

A tsunami inundation vulnerability index is developed to assist coastal managers in quickly assessing the relative vulnerability of sections of dune, while simultaneously identifying the nature and location of weaknesses. At the local level this index may be used to effectively allocate management resources, while at a regional level it can be used in coastal development and hazard planning. Relative to current field survey–based methods of determining tsunami inundation risk, the GIS-based procedures and vulnerability index developed here offer significant improvements in accuracy and efficiency at local to regional scales.