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

Coastal landforms are created by the way the sea and the edge of the land surface interact.

The rocky cliffs and headlands along Otago’s coast have developed during the major stages of geological history – from the formation of Gondwana to the eruption of the Dunedin volcano – and from modern glacial and interglacial deposits. These landforms are known as ‘hard’ features and change relatively slowly as they resist the impact of the sea, wind and waves.

Other parts of the coast are comparatively less resistant and are readily shaped by waves, currents, and winds into a range of landforms, such as beaches, sand spits and dune systems. 

Soft, sandy beaches are sensitive to changes in the natural environment and human activity. The shorelines here can change reasonably quickly (in terms of geological time), creating hazards for local communities.

Healthy dune systems, gravel barriers, 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. When coastal areas are developed or colonised by invasive plant species, these natural systems can lose their ability to respond dynamically to wave energy and the protection they provide is often degraded or lost.

Parts of the Otago coastline have eroded noticeably in recent decades.
Two recent studies investigate coastal changes in Otago – one along the Waitaki coastline and another along the lower Clutha coastline.
These two studies show how the coastline has eroded and changed in the past and estimate the future rate of erosion. Historical erosion rates and sea level rise estimates are used to project the position of the shoreline in the future.

Climate Change is expected to increase the frequency and magnitude of storm events at our coasts. This may affect the severity of erosion impacts along our coastlines and exacerbate coastal erosion hazards in our coastal communities.

For more information on Climate Change in Otago please visit our Climate Change pages. We also have a range of publications and reports available, two of particular interest might be the Waitaki coastline report of the Lower Clutha (Molyneux Bay-Clutha Delta) coastline report.