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Impacts of sea-level rise on the Avon River, Christchurch 

Adaptation case study 4
INFO 283; May 2008

What’s the issue? 

Christchurch is the biggest New Zealand city to be built on a flood plain. As the climate changes, it is likely that Christchurch will face increased flooding in some areas, particularly around the lower Avon River and the area where it flows into the sea. 

To address these concerns, Christchurch City Council undertook a study in 2003 to examine the potential effects of climate change on the Avon catchment and associated coastal areas and to assess how these risks could be managed. 

While the stopbanks on the Avon flood plain currently provide adequate flood protection for most properties, in the future they are likely to be overtopped with greater frequency. This is due to the projected increase in the frequency and intensity of storms, storm surge, flooding and sea-level rise. 

Finding solutions for future flooding risks 

Avon River mouth

The Avon River mouth, Sumner,
Christchurch.

As part of the 2003 study, the Council evaluated how climate change impacts could be integrated into risk management planning for the Avon catchment and associated areas. It focused primarily on an economic analysis of likely damages, and the response options available to local government to mitigate these. 

Options considered, and results of the study show:

  • Minimum floor levels would be particularly beneficial in areas with relatively low stopbanks. The report recommended that Christchurch City Council considers setting different minimum floor levels for each ponding basin. 
  • Subdivision restrictions would not offer a net aggregate economic benefit in terms of preventing flood damage over the next 100 years. However, it was recommended that this option should be revisited in the future. 
  • Stopbank improvement – only one area (Hulverstone stopbank) would show an immediate benefit from improvements. Other areas could be worth upgrading in the future but would not benefit under current conditions. It was recommended that this option be revisited in the future. Heathcote River in flood
    Heathcote River in flood.
    Heathcote River

    Heathcote River.

  • Tidal barrages were considered unlikely to be feasible. They would not yield a net benefit and have considerable environmental and amenity issues. This option was not recommended for future consideration. INFO 283 Heathcote River. Heathcote River in flood. 

Conclusion 

Since this report was undertaken, changes have been made to the City Plan and aspects incorporated into the Urban Development Strategy that seek to reduce the risks to the community from climate change. 

Find out more

Links to further information: 

Publications: 

See Ministry for the Environment publications: 

  • Climate change effects and impacts assessment 
  • Preparing for and adapting to climate change. Look ahead to the future 

These are available on www.mfe.govt.nz/publications/climate/ and by emailing orders@mfe.govt.nz 

Contacts: 

Ministry for the Environment 
Contact us for more information about climate change or new initiatives: 
Phone: (04) 439 7400 
Email: info@climatechange.govt.nz 
Address: Ministry for the Environment, PO Box 10362, Wellington 

Christchurch City Council
Contact City Plan Team Leader, City Plan Team, Strategic Support Unit
Phone: (03) 941 8999
Email: info@ccc.govt.nz
Address: Christchurch City Council, PO Box 237, Christchurch 8011