16KB image of NZ sand dunes. Richard Chesher

Key Ideas about Sand Dunes


Sand dunes are vital to the survival of beaches and protect homes and habitats further inshore from salt spray and sand. Beaches, with their associated sand banks and sand dunes, are coastal shock absorbers, diffusing the impact of ocean waves.

Over 100,000 hectares of New Zealand coastline are covered with dunes. Auckland's west coast and the Ninety Mile Beach in Northland have the largest dunes, often extending several kilometres inland. Giant sand dunes over 100 metres high are unusual, perhaps reflecting long periods of dune construction in the past. More often sand dunes are 10 to 50 metres high, representing huge reserves of sand to protect and maintain our beaches.

The soft sands are created by years and years of the water grinding stones and animal skeletons into tiny particles. The sand is a fluid environment, moving all the time, gathering slowly into huge dunes and then, during storms, shifting back out to sea to form a wide shallow bar that trips up the incoming waves. This cycle is important in the long term stability of the shoreline.

The sand dunes are part of the natural cycle of shore protection and the plants and animals that live on them contribute to this dynamic process. Spinifex grass and pingao or golden sand sedge, for example, help trap the wind-blown sand and it's roots hold, but do not completely stabilise, the sand dunes. Imported Marram grass tends to stabilise the sand dunes resulting in a loss of resiliency.

19 KB image of spinifex catching sand. R. Chesher

Unfortunately, sand dunes are also convenient places to mine sand for making glass or to obtain minerals such as iron. Sand dunes also block rapid access to the beach as well as the scenic view for houses built near the beach. Many of New Zealand's sand dunes have been degraded by mining, road construction, residential and tourism construction, heavy recreational use (including kids sliding down the face of dunes), pets (dogs chasing and killing birds nesting on dunes), imported plants, and off-road vehicles.

Several regional councils, like Environment Waikato, Bay of Plenty and Auckland, have fostered community based "Dune Care" or "Beach Care" projects to help restore the sand dunes and protect the beaches.

References


Restoration of native plant communities on sand dunes. Bergin and Herbert 1994. What's new in Forest Research. No. 232. New Zealand Forest Research Institute, Private Bag 3020, Rotorua.

Dune Care. by Eric Hamilton, Forest and Bird February 1996.

Sand Dunes in the Waikato Region. Environment Waikato Regional Council. Sea Week 1996.


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