Coastal Erosion 

Coastal erosion is the wearing away of land and beach sediments by waves, tidal currents, drainage or high winds. 

Tautuku Peninsula - Catlins

Tautuku Peninsula - Catlins

Coastal landforms result from the interaction of the sea with the edge of the land surface. The rocks that form the cliffs and headlands along Otago’s coast represent the major stages of geological history from the formation of Gondwana to the eruption of the Dunedin volcano, and modern glacial and interglacial deposits. These ‘hard’ features are generally more resistant to physical processes, and changes in shoreline position will therefore occur relatively slowly.

Where the coastal boundary consists of material such as sand and gravel (‘soft coasts’), the prevailing physical processes will shape it into a range of landforms, such as beaches, sand spits and sand dunes. The main processes affecting this type of coastline include:

  • Water level and tides
  • The wind and wave regime
  • Onshore topography (river catchments) and offshore bathymetry
  • Sediment movement and characteristics.

Soft, sandy beaches are sensitive to both natural environmental changes and human interference, which can lead to reasonably rapid (from a geological perspective) rates of shoreline change. Where erosion of the shoreline becomes the dominant process, a potential hazard may be created for communities or assets near the coast.

Healthy dune systems, gravel barriers and coastal wetlands and marshes can all help protect inland areas from erosion and inundation by buffering wave energy, slowing water speeds and reducing the movement of coastal sediments. Often where coastal development has occurred these natural systems are degraded or lost.

Parts of the Otago coastline have experienced noticeable coastal erosion in recent decades, this is described in the Otago Regional Council Molyneux Bay Report and DCC coastal report.

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