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Our coast

Coastal development and erosion

This page currently has information on coastal development and erosion. There are many other coastal issues which could be covered. Further information on several issues is provided on the coastal projects and coastal publications pages.

Coastal development

Auckland's coastal environment is under extreme pressure. While we may not notice the small, incremental changes to the region's beaches, over time they have significantly altered our coastline.

Changes to the original character of our coast include:

  • Built seawalls - they protect against erosion but change the shoreline shape.
  • Depletion of natural vegetation.
  • Depletion of 90% of dunes - leaving areas more prone to flooding and erosion.

Rugby on beach

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City beaches

City beaches are small, sheltered systems. They are located from Long Bay to Kawakawa, and within Manukau and Waitemata Harbours. City beaches are threatened by urban development which results in a loss of natural character and affects their natural ability to buffer against erosion.

What is coastal erosion?

Coastal erosion is the long term (20 years or more) landward movement of the coastline.

Change in the position and shape of the coastline is a normal process, and is almost always the result of both human activity and natural processes that erode the coastline. However, with the region's growth set to double over the next 50 years, any development needs to be carefully managed to ensure it does not exacerbate erosion issues.

Typical causes of beach erosion include:

  • Change in sediment supply (eg seawalls blocking sediment falling from cliffs )
  • Wave processes or sea level change
  • Wind removal of sediment
  • Stormwater discharges direct onto the beach
  • Formation of updrift littoral barriers that stop sediment movement (eg groynes, breakwaters
  • Loss of vegetation, which helps soak up heavy rainfall
  • Loss of natural headland control.

Typical causes of cliff erosion include:

  • Weathering, or the effects of wetting and drying
  • Bio-erosion, which is the biological weakening of rock
  • Wave action
  • Increased groundwater levels
  • Overloading by added material, such as fill
  • Landslides, slumping and slipping
  • Loss of vegetation.

How do we manage coastal / beach erosion?

The Coastal Hazard Strategy and Coastal Erosion Management Manual provide guidance for managing city beaches and erosion. There are a number of key opportunities we can take:

  • Pristine beaches must be protected from development (eg those on offshore islands).
  • Beaches can be re-created to some extent, like Mission Bay and Kohimarama.
  • Sediment sources to artificially nourish beaches are limited, but do exist in backshore deposits on land and offshore and west-coast harbour deposits.
  • In a semi-natural situation, like Long Bay, the potential for restoration through dune reshaping and native planting is significant.

Take this link for the Coastal Hazard Strategy and Coastal Erosion Management Manual.

Like to get involved or need help?

There are a number of volunteer programmes that you can get involved in; from planting riparian banks, reporting on potential pollution hazards and cleaning up streams.

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