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Geographic Area Covered 

The report covers the Wellington region, including coastal areas and river systems potentially affected by tsunami inundation. 

Summary 

This report presents interim tsunami evacuation zone mapping for the Wellington region, developed by GNS Science in 2009. The primary objective is to delineate areas at risk from tsunami inundation using a GIS-based attenuation model. The model calculates inland inundation based on elevation and proximity to the coast and rivers, using a linear attenuation rule. The zones are defined using probabilistic wave heights with 500-year and 2500-year return periods, representing moderate and maximum credible tsunami events respectively. Two evacuation zones are proposed: the orange zone, which may be affected by regional and distant-source tsunami events with sufficient warning time; and the yellow zone, which includes all areas potentially affected by any credible tsunami, including those with little or no warning. The model uses digital elevation data derived from LINZ topographic maps and LiDAR where available. It accounts for attenuation inland (1m drop every 200m), upriver (1m drop every 400m), and across land from rivers (1m drop every 50m). The report emphasizes the need for local validation and future refinement of the zones as better data and modelling techniques become available. Limitations include the resolution of elevation data and the simplified nature of the attenuation model. The report recommends that evacuation zones be updated over time, progressing from simple elevation-based models to more robust simulations and eventually to envelopes encompassing all credible tsunami scenarios. The mapping supports Civil Defence Emergency Management planning and aligns with national guidelines for tsunami evacuation and signage. Overall, the report provides a practical and conservative approach to tsunami risk mitigation in the Wellington region.