We have been working to understand and manage coastal erosion hazards since the 1980's. Our March 2020 study shows updated coastal erosion lines out until 2130.
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What is coastal erosion?
Coastal erosion is the loss of land due to coastal processes such as waves and tidal currents wearing away land, suddenly or over time. Over time this can result in the slow erosion of shorelines and the loss of established dune systems along the coastline.
Erosion along our open coast is influenced by the effects of climate change, such as sea level rise, changes in weather patterns and the increasing intensity of rainfall.
Climate change and sea level rise
Recent natural hazard mapping for Tauranga's open coast
Council recently engaged Tonkin and Taylor (T&T) to undertake a further assessment of the erosion potential along Tauranga’s open coast from the base of Mauao to the eastern extents of Papamoa. The assessment set out to identify and map areas of land along our coastline potentially exposed to coastal erosion taking into account different scenarios of sea level rise.
Sea level rise scenarios are based on the recently released Guideline on Coastal Hazards and Climate Change from the Ministry for the Environment, (2017). This document outlines a recommended adaptive planning assessment that Councils can use in the consideration of sea level rise and when/how to use differing sea level rise scenarios in natural hazard planning.
Guidance on coastal hazards and climate change
This latest assessment updates the results of a previous erosion hazard study by T&T from 2009, and uses an improved methodology, additional beach monitoring data as well as storm observations over the last decade.
The study set out to:
- Identify and assess variables that contribute to coastal erosion;
- Calculate potential erosion distances using recognised methodology;
- Apply current and future sea level scenarios in accordance with the requirements of:
- The NZ Coastal Policy Statement (NZCPS);
- Natural Hazard Provisions of the Bay of Plenty Regional Policy Statement (RPS);
- Proposed Regional Coastal Environmental Plan (PRCEP);
- Ministry for the Environment (MfE) Coastal Hazard Guidelines (2017).
- Map Coastal erosion hazard distances for present day, 50 year and 100 year timeframes across different sea level rise scenarios and probabilities.
The results are a range of potential erosion hazard distances, varying from ‘likely’ to ‘very unlikely’ when considering potential erosion, timeframe and sea level rise scenarios out to the year 2130.
Mount Maunganui to Papamoa Coastal Erosion Assessment Report
Erosion mapping viewer
This viewer gives you the ability to select a specific property, choose a sea level rise scenario and see what the predicted erosion hazard relevant to that property could be over time.
There are a number of variables that influence erosion risks for a specific property, over time, including:
- dune height
- level of (pre)existing erosion at that point of time
- height of sea level rise
- storm event
- the characteristics of coastal soils.
It is important to note that different properties are exposed to different levels of probability that the hazard will in fact occur, including the likelihood of a projected sea level rise scenario occurring. The reports and modelling results apply to Tauranga’s open coast as a whole and may be superseded by site specific assessments carried out by qualified professionals who use improved or more detailed data than presented in this study.
After opening the viewer, click on the magnifying glass symbol at the top right, then enter the address for the property you would like to see details for.
Erosion mapping viewer
2009 coastal erosion hazard zone update
In 2009, as part of a wider hazard research programme, Tauranga City Council and its advisors looked at erosion processes specifically along Tauranga’s open coast. As part of the development of the operative district plan at that time, the coastal erosion lines were updated. The analysis considered potential/estimated rates of erosion taking into account different sea level rise scenarios.
Coastal erosion hazard zone update (2009) (14mb pdf)
In 1994 we commissioned an assessment of coastal erosion hazards from the Centre for Environmental and Resource Studies (CEARS). CEARS recommended establishing a unified programme of hazard management to deal with the risks associated with coastal erosion and inundation.
Then in 1996 we commissioned a comprehensive coastal erosion and inundation hazard risk assessment – dubbed ‘Project Dune Watch’ – along the Mount Maunganui/Pāpāmoa coastline. This risk assessment identified how coastal erosion and inundation could affect land adjacent to the coast within the following 100 years.
The Project Dune Watch report defined coastal erosion hazard zones based on research utilising enhanced determination technology. The report gave guidance on the degree of erosion risk in each zone, and the planning controls that should be put in place at individual property level.
Project Dune Watch report (1996) (15mb pdf)
Frequently asked questions
We have been working to understand and manage coastal erosion hazards since 1980. Regular assessments and monitoring carried out since then have sought to better understand coastal erosion hazards and ways in which to manage the associated risks.
The last assessment, completed in 2009, updated the coastal erosion lines through the development of the operative district plan, taking the effects associated with climate change into consideration. Regular beach profile monitoring and surveying since then has continued to expand our understanding and knowledge.
This latest assessment builds on this knowledge and provides a comprehensive understanding of the extent to which our coastal environment is changing, taking into account sea level rise projections.
These erosion hazard maps identify areas of our coastline that are at risk of erosion by the sea. The maps are an output of modelling by Tauranga City Council and our technical advisors.
The maps show the predicted extent of open coast erosion out to the year 2130 and includes the impact of predicted sea level rise (SLR). Present day coastal erosion hazard areas have been shown for comparison with future erosion and sea level rise scenarios.
The coastal erosion maps illustrate areas likely to be affected by erosion for the open coast based on various time and sea level rise scenarios.
Nine scenarios have been mapped which reflect the likelihood of erosion occurring within the timeframes of present day, 2080 and 2130.
The scenarios mapped also identify coastal erosion extents as 'likely' or 'extremely unlikely' (but still possible), these scenarios are shown for each timeframe.
Broadly speaking, across the different timeframes, the areas identified as having a 66% probability are considered as ‘likely’ to be affected while areas with 5% probability are ‘extremely unlikely’ to be affected.
A specific web viewer has been created to allow you to view any property in relation to this hazard. This website includes links to the technical study along with a series of helpful reports and links where further information can be found.
Erosion mapping viewer
The purpose of the Resource Management Act (RMA) is to promote the sustainable management of natural and physical resources. It requires that a number of nationally important matters be recognised which include the management of significant risks from natural hazards. Particular regard must also be given to the effects of climate change.
The avoidance or mitigation of natural hazards is one of the key functions of council in giving effect to the RMA. A similar requirement also exists for councils under the Building Act, Local Government Act and Civil Defence Emergency Management Act. Consequently, we are required to have a good understanding of the areas potentially at risk from natural hazards to support appropriate land-use planning and development decisions.
The New Zealand Coastal Policy Statement also directs councils to identify areas that may potentially be affected by coastal hazards over a timeframe of at least 100 years. Mapping is the most accepted method to identify hazard-prone areas and provide the greatest level of certainty to the public.
Climate change refers to the changes to the present-day climate associated with the effects of global warming. Climate change is projected to have a significant impact on the land near the coast. This impact will come about especially through sea-level rise and intensification of storm events.
National and regional analysis of climate change impacts have also been carried out by the National Institute of Water and Atmospheric Research (NIWA).
Different sea level rise scenarios reflect different assumptions about ocean warming and the melting of land-based ice.
The four sea level rise scenarios that have been selected for use in this study are based on up-to-date technical guidance from the Ministry for the Environment on projected sea level rise. This guidance is based on the scenarios presented by the Intergovernmental Panel on Climate Change (‘the IPCC’).
The scenarios used by the IPCC are commonly referred to as ‘Representative Concentration Pathways’ (RCPs). The primary purpose of the RCPs is to provide projections of greenhouse gas concentrations which correspond to changing energy levels within the atmosphere.
Historic sea level rise in New Zealand has averaged 1.7 ± 0.1 mm/year with the Bay of Plenty exhibiting a slightly higher rate of 2.1 ± 0.1 mm/year. Climate change is predicted to accelerate this rate of sea level rise in the future.
NIWA have developed a range of SLR projections for Tauranga based upon recommendations from the Ministry for the Environment (2017) or use in planning processes.
This guidance recommends the use of a range of sea level rise scenarios with a need to take a long-term view towards sea level rise scenarios up to 1.6m.
It is expected that sea level rise will exacerbate current coastal erosion in terms of scale and frequency of erosion events. It is also likely to increase the frequency of damaging storm/weather events. For example, a modest sea level rise of 0.3m (possibly reached by 2050), is likely to change a present-day rare storm event into an annual event.
We have an obligation to make hazard information we hold available to the public under the Local Government Official Information and Meetings Act 1987. It will be made clear on any Land Information Memorandum (LIM) requested for a property within a hazard area, that council holds information in respect of coastal erosion and for the property which has been derived from a coastal hazard study.
We are required to make information, such as the Coastal Hazard Study, available upon request. We cannot advise you about any effect this information may have on property value or insurance.
It is recommended that professional advice is sought from a property valuation or insurance expert about any questions you may have regarding these matters.
The receipt of this information allows us to continue to plan for subdivision and built development along the open coast and also understand how erosion may occur out to 2130, based upon a range of sea level rise scenarios. This will include consideration of regulatory provisions to manage future development (including intensification) within these risk zones and how to best adapt to changes in hazard information in the future.
Last Reviewed: 15/07/2021