Paradise Explained

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A happy accident of nature has blessed Australia with its unique coastal systems — and some of the best beaches in the world, write Andrew Short and Colin Woodroffe

What makes Australian beaches so good? The answer is a combination of six factors related to geology, climate, oceanography and marine biota.

Geology provides two factors: the number of headlands that often form attractive boundaries, backdrops and viewing platforms to many beaches, such as at Noosa in Queensland, Bondi in New South Wales, Bells in Victoria, Waitpinga in South Australia, Cottesloe in Western Australia and Mindil beach in the Northern Territory. The headlands also help us divide the coast into more than 10,000 beaches.

The other geological factor is the usually clean, white–to–yellow quartz sand that stems from ancient granite rocks, the source of half of Australia's beach sand.

Around half the coast and on many coral sand cays, the marine biota provides carbonate detritus to form equally clean, white beaches. The carbonate material derives in the south from the inner continental shelf, in quieter environments from seagrass meadows and in the north from fringing coral reefs.

Due to its predominantly arid climate, half the continent has no rivers and has had none for the past 40 million years. This means that very little fine silt and clay is delivered to the southern coast to discolour the water. The result is clean, clear water over the clean, white–yellow sands.

Climate, via oceanography, provides the waves to roll into the beaches, with the southern coast dominated by regular surf all year. Finally, climate, through wind, is also responsible for the extensive dunes that back most of the beaches, including the longest and largest coastal dune systems in the word.

The southern Australian continental shelf is the largest carbonate factory in the world, three times the length of the Great Barrier Reef. Regrettably, we know little about this massive marine ecosystem. Along with having the largest temperate seagrass meadows, there is an abundance of carbonate sediment to build the most enormous beaches and coastal dunes in the world.

Most Australian beaches are undeveloped, unnamed and found in their natural state, with one–third protected in national parks. As a result, Australia has thousands of pristine, undeveloped beaches with clear water, clean sand and surf, usually bordered by headlands and backed by vegetated coastal dunes.

Australia's coastal dunes occupy 23,500 square kilometres, backing 12,774 kilometres of the coast, or 85 per cent of the sandy coast. They are normally absent from very small, embayed and very low–energy beaches. On average, coastal dunes have a mean elevation of 10 metres, a maximum elevation of 26 metres and extend 1.8 kilometres inland. They contain 280 cubic kilometres of marine sand, blown inland from the beaches. This represents an average of 22,000 cubic metres of dune sand for every metre length of beach.

The dune systems therefore represent a massive volume of sand, sourced from the marine environment and transported onto the beach by waves. Occasional strong winds then blow this sand inland grain by grain, until the dune systems eventually become stabilised and vegetated. They form a major component of the Australian coastal environment.

Some of Australia’s major coastal suburbs and resorts are built on dunes, including Bondi and Manly in New South Wales, the Gold Coast in Queensland and much of coastal Adelaide and Perth.

While most Australian dunes are covered in dune vegetation and are stable, they are easily destabilised and re–activated by vegetation disturbance and removal, particularly along the seaward edge. Management of these systems therefore revolves around maintaining vegetation cover, which in turn supports the associated dune flora and fauna.

Residential and tourist developments now cover some dune systems located near major cities and some are mined for sand to build those same developments. The vast majority however, remain in a natural state, with many located in national parks and reserves. In terms of area, they are our most extensive coastal asset.

Andrew Short is honorary professor in the School of Geosciences at the University of Sydney. Colin Woodroofe is professor in the School of Earth and Environmental Sciences at the University of Wollongong. This edited except is taken from their book, The Coast of Australia, Cambridge University Press, Port Melbourne, 2009.