Multi-hazard analysis and mapping in support of coastal city growth planning and resilience building

Abstract

High growth in Tauranga is causing increased pressure to develop hazard-prone land. A key tool in evaluating safer potential growth areas is the quantification and spatial mapping of individual natural hazards. In a hazard-rich, coastal environment like Tauranga a newly developed multi-hazard mapping technique gives additional clarity through direct comparison of total hazard levels across the city. By aggregating individual hazards, a summative multi-hazard rating for each part of the city can be developed as a strategic decision support tool, aiding in city planning and engineering decision making. This study initially quantifies Tauranga’s natural hazards of sea-level rise, tsunami, flooding, storm surge, earthquake, coastal erosion, liquefaction and landslides. Each hazard is spatially represented through hazard maps and additionally processed to enable aggregation with other hazards to produce the multi-hazard rating. Individual hazards are combined by application of a new technique to create a summative multihazard model representing the aggregated hazard at each point of the city. This allows an area with tsunami, liquefaction and storm surge as dominant hazards to be directly compared with an area of different hazards such as flooding and landslides. The resultant spatial map provides a visual interpretation of the accumulated hazard level at all points of the city. Map results show the highest aggregated hazard areas in Tauranga are along the coast. Lower hazard areas suitable for urban growth are distributed mostly away from the open coast on slightly elevated topography. Isolated high exposure pockets are additionally located throughout the city. This multi-hazard comparison can be adopted to guide city growth and enable targeted investment in resilience building projects.