Coastal inundation tool

The tool uses a 'bathtub model' to show  ‘static’ water levels. A bathtub model simply means treating the ocean like a bathtub, that fills up the same way that a tub does when you add water. The lower parts fill up first, and the water rises at the same level everywhere. The tool does not include the effects of currents, friction, waves or other hydraulic processes that affect water movement or inundation.

The tool shows:

• Connected inundation (blue shaded areas), which represent areas where water could flow directly (or via waterways) to the sea for the chosen water level.
• Disconnected inundation (green areas), which represent areas that are at or below the chosen water level, but may have no direct flow path to the sea (e.g. due to beach ridges or flood protection structures).  These areas may still be affected by coastal inundation in some way, e.g. via groundwater.

The tool uses the best currently available water level and ground elevation information. All water levels and land elevations are provided relative to Moturiki Vertical Datum 1953.

Points to note

The very first mapped water level for all locations shows the area that is likely to be inundated with a high tide. This is generally 0.2 m below the mean high water springs level (MHWS) which is the place on the shore where spring high tides reach on average over a period of time (often recognised by the upper line of debris on the beach). All higher mapped water levels only show areas that would not normally be inundated by a high tide.

The tool is not intended to provide specific information that could be used to define actual coastal inundation hazards or minimum floor levels for specific properties.

Some areas on the west coast are not included in the tool. However, due to their steep topography, these areas are generally not expected to be susceptible to coastal inundation.