Sea-level rise over the next 100 years is likely to significantly increase the risk of coastal inundation and erosion, and the impact on coastal communities.

Beach erosion at New Brighton, July 2001.

The New Zealand Coastal Policy Statement (NZCPS) requires the identification of coastal hazard risk over at least 100 years. So along with all regions in New Zealand, we need to be looking now at which areas are likely to be impacted by coastal inundation and coastal erosion and the associated risk out to at least 2115.

The Coastal Hazard Assessment Report 2015 [, ] was the basis for the notification of the proposed changes to the District Plan. While the coastal hazard provisions have been removed from the District Plan process, the information in the report will still inform Council processes and the Council's statutory obligations, including LIM notations and issuing building consents.

What are we doing now?

We are actively planning for anticipated changes that will increase the risk of coastal hazards.

We are working with other agencies and communities to reduce the risk from natural hazards where we can, or to lessen their effects by planning for response and recovery.

  • Identifying and mapping areas susceptible to coastal inundation and coastal erosion
  • Making provisions for flooding in the Proposed Replacement Christchurch District Plan(external link)
  • Working with other agencies to develop regional strategies and work programmes to increase our resilience to nature's challenges
  • Preparing a Natural Hazards Strategy, that will act as a framework for policy and decision-making around natural hazards on an ongoing basis
  • Dealing with sand management/dune repair, dealing with minor and early erosion issues before they develop, and sand-fencing and dune-planting to trap sand and rebuild beach profiles
  • Looking at, as part of the Land Drainage Recovery Programme, area-wide flood mitigation options, including large scale physical works, to reduce the risk of flooding to the city’s most affected areas and to restore flood risk to its pre-earthquake condition. The potential for a tidal barrier across the Avon-Heathcote estuary is one measure which is in the early stages of being explored.
  • Installing tsunami warning sirens from Waimairi Beach to Sumner 

Infrastructure Planning

The Council has been working to ensure that its infrastructure is resilient to the effects of coastal hazards. For example different wastewater systems are being constructed including lift stations, pressure sewer systems and vacuum sewer systems.

The long-term options for managing river and tidal flooding in certain areas is connected with the future use of the residential redzone. The Council has started early technical work to determine where stop banks would ideally be placed and what other infrastructure implications there are. We are developing infrastructure scenarios, with flexibility as to detailed placement of stopbanks, depending on what is decided regarding the future use of that land.

What more can we do?

We will continue to live in coastal areas because of the value in doing so but we need to adapt to changing coastal conditions.

There are many options for reducing the risk to people and property from coastal hazards. These range from engineering solutions such as sea walls through to working with nature, like dune restoration projects.

There are also planning responses to reduce coastal hazards. This would involve identifying areas likely to be affected by coastal hazards and applying planning tools to control or avoid certain activity in these areas.

All options have financial, environmental and ecological impacts that need to be carefully considered by the Council and community.

Monitoring 

Environment Canterbury(external link) has also collated and analysed historic shoreline positions from photographs and survey plans going back 60-70 years. This is how we know how the shoreline has moved over the past several decades.

In the past 25 years Environment Canterbury has regularly surveyed shoreline positions and beach and dune profiles on the Christchurch open coast between Taylors Mistake and the Waimakariri River. 

The surveys give us detailed information about:

  • The volume of sand in the beach
  • Coastal dune positions and their elevations
  • How much the beach and dunes have eroded during coastal storm events
  • How well the beach and dunes recover after storms

The level of the sea is also monitored by sea level recorders (sometimes referred to as tide gauges) at Lyttelton, Sumner and Ferrymead Bridge. These measure the changes in elevation of water throughout tidal cycles and during coastal storms (short-term sea levels). They also help monitor any longer term trends in sea levels (such as sea-level rise) over many years.