We have engaged Tonkin & Taylor to assess coastal hazards for the entire Christchurch district. This assessment will help us with coastal hazards adaptation.

Why we need an updated coastal hazards assessment

The Ministry for the Environment has advised councils to work with communities to undertake coastal hazards adaptation planning and decision-making starting with the identification of areas at risk from coastal hazards over the next 100 years.

For good planning, we need the best available data about coastal hazards and processes so we can predict risks. While there have been a number of coastal hazards assessments completed in the past, we have chosen to undertake a full update to:

  • allow new technical information to be incorporated, including extreme water level and sediment supply data.
  • fully respond to peer review recommendations and national guidance.
  • broaden the scope to include the entire Christchurch District coastline and include the hazard of rising groundwater due to sea-level rise.
  • be more user friendly and accessible to communities to improve understanding and awareness.

Inevitably, there are uncertainties. However, the data will allow us to broadly understand possible risks and support sound adaptation planning discussions with communities and robust decisions by the Council. By using a range of hazard scenarios in this assessment, it is not anticipated that further updates will be needed for a while.

There are four key steps in the process to undertake the Coastal Hazard Assessment, which draws on the international risk management standard ISO 31000:2019.

Key steps in undertaking the coastal hazard assessment

Scoping

Review of direction, guidance, previous studies and new technical information.

Gather input data and identify gaps.

Test and confirm purpose, use, outputs and scenarios.

Methodology

Identify uncertainties and implications for use.

Determine assessment level and spatial extent.

Develop, test and refine methodology based on the latest techniques and available information.

Provide example outputs.

Analysis

Using the agreed methodology, undertake technical hazard analysis.

Reporting

Develop final outputs and supporting communications including:

  • Interactive online platform with maps showing modelled hazard for various scenarios.
  • Summary report of findings and supporting background reports.
  • Technical review register.

The scoping and development of the methodology was completed at the end of 2020, analysis is underway, and the final report is expected to be publicly released in the second half of 2021.

The entire process is being critically reviewed through a rolling technical review by Derek Todd, principal coastal hazard scientist at Jacobs, to provide confidence in the integrity of the technical hazard information. Derek brings a wealth of local knowledge of coastal processes in Canterbury, which has been supplemented with oversight from Environment Canterbury coastal scientists.

We’ve tested the approach with representatives from community groups with interests in technical hazard information and/or environmental issues in late 2020. The purpose of this engagement was to understand potential community perceptions and concerns and to seek assistance in developing communications and supporting information.  Read the meeting notes [PDF, 423 KB].

There will be further opportunities for these community groups to support the development of the final outputs in stage 4.

Once the 2021 Coastal Hazards Assessment is complete and approved by Council it will be publicly released. There will be a range of resources and communication tools provided to support the public understanding of this technical information along with opportunities for members of the public to talk to and question staff and technical experts.

The 2021 Coastal Hazards Assessment is only the first part of the adaptation planning process. It will identify where hazards may occur in the future at a neighbourhood scale, but not how these risks will be managed.

The Coastal Hazards Adaptation Planning Programme will work with affected communities to identify pathways for how different communities could adapt.

The adaptation planning process puts the community at the centre of decision-making so there will be plenty of opportunities for involvement and feedback.

Any changes to the District Plan to manage existing development will only be proposed following engagement with communities on possible options for management.

The Christchurch Coastal Hazards Assessment: Methodology and Approach Summary [PDF, 3.1 MB] outlines the approach to undertaking the Coastal Hazards Assessment developed by Tonkin & Taylor and agreed as fit for purpose by Jacobs (technical reviewer), Council and Environment Canterbury staff.

This is a technical overview for those interested to understand more about how the Coastal Hazards Assessment is being developed, what assumptions have been made and why.

An overview of the purpose and context of this report is provided in this cover letter [PDF, 506 KB].

We recognise that the uncertainties of climate change projections are often a key concern to communities.

Any information related to the future conditions of natural and social systems has uncertainties that users of this information should be aware of. This does not mean that the results are inaccurate, but that the way they are used and interpreted needs to reflect this uncertainty.

What we map and the way we show this information also helps to understand some of the uncertainties and reduces assumptions about management being made before we engage with communities.

We are intending to map a wider range of scenarios, increments of sea-level rise, and likelihoods, and will be looking at different ways of presenting the results.

The increments of sea-level rise used in the assessment are based on Representative Concentration Pathways (RCPs) which have been endorsed as scientifically robust by the Intergovernmental Panel on Climate Change (IPCC).

Each scenario is based on how we as a global community might respond to climate change now and into the future, with the four scenarios depending on the amount of greenhouse gas emissions we continue putting into the atmosphere.