Predicting Auckland’s exposure to coastal instability and erosion
Author:Ross Roberts, Natasha Carpenter, Paul Klinac, Patrick Knook, Ben Westgate, Rebekah Haughey, Tom Shand, Richard Reinen-Hamill, Tonkin and Taylor
The Auckland region has over 3,200 km of coastline including three major harbours and a range of sandy beaches and dunes, rocky shores and cliffs, estuaries and offshore islands. As well as a long and diverse coastline, Auckland has the largest population density to coastline ratio in New Zealand. As a result, the city has a high exposure to coastal hazards including coastal instability and erosion. These hazards can present a safety risk, adversely affect property and infrastructure, and damage or destroy cultural and environmental sites.
A study undertaken in 2006 is the basis for the current coastal erosion rules within the Auckland Unitary Plan. No more up-to-date information related to the potential exposure of Auckland’s coastline to erosion was available at the time of the plan’s development.
To fill this knowledge gap, a programme of research has been undertaken to identify, at a regional level, the Area Susceptible to Coastal Instability and/or Erosion (ASCIE). ASCIE is the area landward of the current coastline that is at risk because of coastal erosion or instability caused by coastal erosion. Titled “Regional Assessment of Areas Susceptible to Coastal Erosion and Instability”, this study was undertaken for Auckland Council by Tonkin + Taylor Ltd., with a peer review by the University of Auckland. The study forecasts the areas of Auckland’s coastline that could be affected by coastal erosion and instability under a range of climate change (sea-level rise) scenarios and timeframes.
A non-technical overview of the study is given in Part 1 of this Technical Report while the detailed study as reported by Tonkin + Taylor is presented in Part 2. The intent of this separation is to provide a Council synopsis and interpretation for non-technical readers.
Auckland Council technical report, TR2020/021
Published in February 2021.
Regional assessment of areas susceptible to coastal instability and erosion
Regional Assessment Prepared for Auckland Council by Tonkin & Taylor Ltd, January 2021
Frequently asked questions
Why has this report and maps been produced now?
The report and associated maps are an update of an earlier report which predicted coastal erosion for the Auckland region. Produced in 2006, this needed updating to include current scientific knowledge, particularly relating to the effects of climate change.
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. This can subsequently result in the instability of dunes and cliffs as the base erodes.
What is meant by climate change?
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.
What will future sea level rise mean for coastal erosion?
It is expected that sea level rise will increase the current rate of coastal erosion. It is also likely that a warming climate will increase the frequency of damaging storm/weather events which will accelerate these effects.
What sea level rise scenarios were used in this study?
The sea level rise scenarios selected for use in this study are based on the most up-to-date available 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. Each RCP has been correlated with increasing sea level rise by NIWA. For this study, we followed Ministry for the Environment guidance by using the RCP8.5 high scenario (1.52 m sea level rise over the next 100 years), and the RCP8.5 median scenario for three timeframes:
- 30 years (0.28 m sea level rise)
- 50 years (0.55 m sea level rise)
- 100 years (1.18 m sea level rise).
Why have coastal erosion maps been produced?
The New Zealand Coastal Policy Statement 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 help provide the greatest level of certainty to the public.
Auckland Council also has requirements under the Resource Management Act (which requires that particular regard must also be given to the effects of climate change), the Building Act, the Local Government Act and the Civil Defence Emergency Management Act to have a good understanding of the areas potentially at risk from natural hazards to support appropriate land-use planning and development decisions.
What existing or historical information already exists?
We have been working to understand and manage coastal erosion hazards across the region since early 2000 when the Auckland Regional Council instituted a programme to monitor the coastline of thirteen beaches across the region. In 2006, Auckland Regional Council commissioned a study to better understand the coastal erosion hazard and how to better manage its associated risks. The findings of the 2006 study informed the current Unitary Plan provisions.
How is the new report different?
The new assessment (2020) builds on the earlier findings and provides a better understanding of the extent to which our coastal environment is changing, taking into account sea level rise projections.
What are the regional coastal erosion heat maps in the report?
The coastal erosion heat maps in the report show the predicted extent of coastal areas that may be susceptible to instability and erosion out to the year 2130. They provide an illustration of a range of land instability and erosion distances for both cliff and low-lying shorelines along Auckland’s coastline.
Will these maps be shown on Auckland Council’s online maps (GIS)?
Yes, the results are also presented in an online map format on Auckland Council’s GIS system GeoMaps under the ‘Development Restrictions’ and ‘Geology and Geotechnical’ layers.
How will this information affect the use or development of private property?
This is a regional scale study. The reports and modelling results apply to broad areas and may be superseded by site specific assessments by qualified professionals who undertake more localised assessments than presented in this study.
Could this information affect the value of private property?
Auckland Council is not able to advise on what, if any, effect this information will have on property values. Advice on this should be sought from the appropriate professionals.
Could this information affect my insurance?
Auckland Council is not able to advise what effect, if any, this information may have on individual insurance policies. Advice on this should be sought from insurance providers.
For more information about insurance, please read the letter to Auckland Council from the Insurance Council of New Zealand, March 2021.
How could this information be used in subdivision and land use consents under the RMA?
The Auckland Unitary Plan already has rules relating to activities in coastal erosion hazard areas to ensure that the risks are appropriately managed. The new information presented in this report will also be able to be considered in planning decisions. Because the new study was undertaken at a regional scale, it provides a high-level analysis which will be used to identify if more detailed assessments are needed to support the consent application. These will be done by qualified professionals working for the applicant.
How could this information be used in building consents under the Building Act?
The Building Act states that building consent authorities must refuse to grant a building consent for construction of a building, or major alterations to a building, if the land on which the building work is to be carried out is subject or is likely to be subject to one or more natural hazards, and appropriate hazard minimisation provisions are not proposed. This includes coastal erosion.
Because the current study was undertaken at a regional scale, it cannot be used to confirm if a site is ‘likely to be subject to one or more natural hazards’ at the level of detail required for a building consent. The results of this report can be used to help identify if more detailed assessments are needed to support the consent application. These will be done by qualified professionals working for the applicant.
Where can I find more information?
Auckland Council 2021
FAQs updated 28 May 2021