Coastal and harbour inundation

Coastal and harbour inundation happens when an increase in sea level enables seawater to flood normally dry low-lying land. This is typically driven by storms, where low air pressure and large waves caused by strong winds combine to create a storm surge. This can be worsened by high or spring/king tides.  Climate-induced sea level rise will increase the extent and frequency of inundation, eventually leading to sunny day flooding where flooding occurs with no storm.   Other terms for coastal inundation include ‘coastal flooding, ‘ocean inundation’, ‘storm tide flooding’ and ‘flooding from the sea’. 

The information from the coastal and harbour inundation studies is used in the following council processes:   Future land use planning, to aid in planning for and understanding the effects of natural hazards on existing land uses, potential subdivisions and growth management.   Current and future infrastructure planning, in the consideration of upgrades to existing infrastructure, provision of infrastructure and understanding the long-term effects on the operation and performance of infrastructure.   Building consent processes, and applications for new building consents.   Subdivision consent and landuse consent assessments.   Land information memoranda (LIM).   As per national direction that came into force on 15 January 2026, Council is required to use the best available information when assessing risks and making decisions, such as in building consent processes. As of 2 February 2026, the Bay of Plenty Regional Council is still finalising their formal final sign off processes for the coastal inundation maps, meaning that some information in the maps may change. The maps will be further updated in the future as Council ongoingly improve and review natural hazards data whenever new information becomes available.

Coastal and harbour inundation maps identify land potentially at risk of seawater flooding for various sea level rise scenarios and storm event likelihoods. Coastal and harbour inundation is caused by storms and can be worsened by high or spring/king tides.     

Flood hazard maps identify land potentially at risk of flooding in an extreme rainfall event (also referred to as flooding from rainfall or stormwater flooding). For Tauranga, flooding from rainfall is typically caused by extreme rainfall events beyond the capacity of the city’s drainage system. Heavy rainfall can also trigger landslides. More information on landslides. 

Coastal erosion maps identify land potentially exposed to coastal erosion for different sea level rise scenarios. Coastal erosion is the loss of land due to coastal processes such as waves and tidal currents wearing away that land, suddenly or over time. More information on Coastal Erosion. 

 Tsunami inundation maps show the area of land that could potentially be flooded by a tsunami caused by a rare offshore earthquake that has a wave height ranging between 8m and 15m along the Bay of Plenty coast. Tsunami are a series of waves caused by significant disturbance of the ocean such as earthquakes, landslides, and volcanic eruptions. More information on tsunami. 

We continually review data we hold about natural hazards to ensure we have the latest information available for our community; this includes natural hazards such as flooding from high rainfall, tsunami and coastal erosion. More information on natural hazards in Tauranga.

The coastal and harbour inundation maps identify land that is potentially at risk of flooding from the sea, especially during storms, both with and without sea level rise. The coastal and harbour inundation maps are not a prediction of flooding. Modelling dynamic events such as storms is complex and requires specific inputs for tide, wind, and shoreline shape. Instead, the maps are an estimate of areas susceptible to flooding during storms at current sea level and as sea level rises.

Councils are required to manage natural hazard impacts. Maps are considered the most accepted method to identify areas susceptible to different hazards and provide the greatest level of certainty to the public.   The requirements for councils to manage natural hazards are set out under several different pieces of legislation including the Resource Management Act 1991, Building Act 2004, Local Government Act 2002, and Civil Defence Emergency Management Act 2002.

You can see and explore the maps online. This viewer allows you to select a specific property and find the current coastal and harbour inundation area as well as potential flooding for a range of sea level rise scenarios and storm event likelihoods. Coastal and harbour inundation map viewer  

You can also view the 1% AEP storm with 1.05m sea level rise scenario under ‘natural hazards’ and ‘coastal and harbour inundation’ on our online GIS system MAPI. 

Some factors have not been included when determining the extent and depth of flooding. These factors include:    

• All existing private protection structures which may have been installed around a property. In the majority of cases the design, quality and maintenance of such structures are unknown.
• Changes to landforms following the topographic measurements have not been considered when producing the maps. Topography for this study was measured in 2018-19. 

To identify properties that are affected by coastal and harbour inundation we use a map for a 1 in a 100-year storm with a sea level 1.05m higher than today’s. This is the map that any new subdivision must use to inform their design. Across Tauranga 6,900 properties are identified as being at risk of flooding by the updated coastal and harbour inundation map. Of these, approximately 5,400 properties were identified by the 2019 harbour inundation mapping. The new data supersedes the 2019 harbour inundation data held by Council.

The Building Act 2004 requires consideration of whether the land is likely to be subject to one or more natural hazards. As such, when assessing building consent applications where the proposed building or the subject property falls fully or partly within the coastal and harbour inundation areas, the consent application will be subject to an assessment under sections 71 and 72 of the Building Act 2004.  Find out more about the process and freeboard level to be used in any building consent application.   

The Resource Management Act 1991 (RMA) requires councils to consider whether a subdivision or land use consent is exposed to a significant risk from natural hazards. 

The National Policy Statement for Natural Hazards 2025, which came into effect on 15 January 2026, builds on this by requiring both applicants and councils to manage current and future natural hazard risks, including the impacts of climate change.
Find out more about the required process and considerations to be used in any consent application.   

The council has an obligation to make hazard information that it holds available to the public under the Local Government Official Information and Meetings Act 1987. Where a property has been identified as subject to coastal and harbour inundation in a 1% AEP storm with 1.05m sea level rise, the information will be included on any Land Information Memorandum (LIM) requested for the property. The LIM information will direct the reader to the council’s natural hazard webpage and include a statement that the information relates to city-wide studies and may not reflect the on-site situation or investigations and mitigations done at a property level. 

A Land Information Memorandum (LIM) is a report that provides selected information about a property that council holds. This includes information that identifies special features or characteristics of the land, for example, information about natural hazards.  Information on LIMS.

The Insurance Council of New Zealand has provided Tauranga City Council with an overview of how modelling and data on natural hazards affects property insurance. Information for Property Owners Insurance Letter.  We recommend it is best to talk with your own insurer for more details specific to your property. 

Coastal and harbour inundation can lead to flooding of low-lying land around rivers and streams. The higher sea level during a storm causes water to back up in the river causing flooding inland from the coast.

Our changing climate is projected to have a significant impact on the land near the coast through sea level rise and the intensification of extreme storm events. Information about the global impact of our changing climate is provided in the Sixth Assessment Report of the United Nation’s Intergovernmental Panel on Climate Change (IPCC). National and regional analysis of climate impacts have also been carried out by the Earth Sciences NZ (NIWA) on behalf of the Ministry for the Environment. 
Climate change projection.  

Rising sea levels will increase the area exposed to flooding, as well as increase the frequency of damaging or disruptive coastal and harbour inundation. For example, a modest sea level rise of 0.3 m to 0.4 m could turn what currently is a rare coastal and harbour inundation event (e.g. with a 1% chance of happening in any year), into an event that will occur on average once a year (source: Parliamentary Commissioner for the Environment, 2015)

The use of different sea level rise scenarios reflects the uncertainty in predicting future emissions and in how the atmosphere, ocean, and ice sheets (glaciers, polar ice caps, etc.) will respond to our changing climate. By considering a range of sea level rise amounts we can account for the array of different sea level rise projections reducing the risk in our uncertainty.      

From 1900 to 2020, sea level around New Zealand has increased by approximately 20cm. Our changing climate is predicted to accelerate this rate of sea level rise into the future. 

The rate of sea level rise in the future is very uncertain as it is dependent on what we do. The below graph shows the past records of sea level in Tauranga and around New Zealand as well as the range of future sea level rise projections. Note future projections do not include vertical land movement. 

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AEP is an acronym for annual exceedance probability. This number is percentage chance that an event of this size or larger will occur each year. You may also hear this described as annual recurrence interval (ARI) or return period (i.e. ‘1 in a 100-year storm’ or ‘100-year storm’).  

These values do not mean that a 1% AEP or 100-year event will only occur once every 100 years. This value is instead the average over a very long period. Changes to our climate will also affect these, such that a 1% AEP event today could be an event that occurs every year in future. 

New Zealand lies on a dynamic plate boundary, and this means our land is always moving. Vertical land movement can be driven by tectonic movement, as well as sediments compacting and subsiding over time. Human influences such as land reclamation and drainage, and groundwater extraction can also cause the land to subside.  

Vertical ground movement is measured using spaceborne radar and global navigation satellite systems such as GPS. However, measurements of vertical ground movement have only been done in New Zealand since 2003. This short record means there is significant uncertainty in current vertical land movement data where the error on measurements can exceed 100% of the values themselves.  

While some national data has previously suggested this area may be rising, more recent measurements indicate the land is likely either static or sinking. Given the uncertainties and the potential for subsidence, it would be unwise to assume land uplift will offset sea level rise in planning and risk assessments.