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Geographic Coverage 

The report covers coastal margins throughout the Wellington Region, including Wellington Harbour, Hutt Valley, Kapiti Coast, Porirua Harbour, and the Wairarapa coastline. 

Summary 

This report, prepared by NIWA for Greater Wellington Regional Council, Kapiti Coast District Council, and Wellington City Council, provides a comprehensive assessment of coastal storm-tide and wave hazards in the Wellington Region. It builds on previous studies by incorporating numerical modelling of storm-tide and wave setup, and presents inundation maps for both present-day and future sea-level rise scenarios. 
 
The study uses historical storm data and advanced modelling techniques to simulate coastal inundation from storm-tide and wave setup. Eight storm events were selected based on their joint probability of high storm-tide and wave heights. These events were modelled using hydrodynamic and wave models (RiCOM and SWAN), with high-resolution LiDAR topography integrated to simulate overland flow and inundation. 
 
Key findings include: 
- Present-day inundation from 1% AEP (Annual Exceedance Probability) events is generally limited to low-lying coastal areas. 
- The highest simulated storm-tide levels reached 1.35 m above Wellington Vertical Datum (WVD-53) in Wellington Harbour. 
- Wave setup significantly increases coastal water levels, especially along exposed coastlines, with total inundation levels reaching up to 2.5 m above WVD-53. 
- Future sea-level rise scenarios (+0.5 m, +1.0 m, +1.5 m) show substantial increases in inundation extent and depth, affecting areas such as Petone, Seaview, Central Wellington, Otaki Beach, Waikanae, and Porirua Harbour. 
 
The report highlights that sea-level rise will make coastal inundation events more frequent and severe. Areas currently safe from 1% AEP events may become vulnerable with even modest sea-level increases. The modelling assumes current topography and does not account for future geomorphological changes. 
 
This assessment provides valuable information for land use planning, hazard management, and climate adaptation strategies in the Wellington Region.