Beaches plus rock/reef flats

The wave-dominated, tide-modified and tide-dominated beaches occupy 96% of the Australian coast. The remaining 4% consist of high tide sandy beaches fronted by fringing coral reefs in the tropical north, or intertidal rock flats right around the coast (see distribution in beach typology). They consist of two types.

14. Beaches fronted by intertidal rock flats

Beaches fronted by intertidal rock flats, and in some cases supratidal rock platforms are scattered right round the Australian coast, with those in northern Australia tending to be fronted by laterite, while local bedrock dominates the southern Australian beaches. This beach type is dependent more on local geology than wave-tide processes and they can occur in low through high wave and tide environments. The intertidal rock flats average 270 m in width and range from 50-3000 m wide. They usually consist of a steep high tide beach with the rocks extending seaward from the base of the beach. The beaches tend to the relatively short ranging between 400-800 m in length, and are usually bounded by rock headlands or reefs. At high tide waves break heavily across the rock flats producing treacherous surf conditions and some of Australia’s most hazardous beaches, particularly along the high-energy southern coast. At low tide, depending on the elevation of the flats, the waves may only break on the outer edge of the rocks, with a bare intertidal rock surface and no wave reaching the beach.

15. Beaches fronted by fringing coral reef

Beaches fronted by fringing coral reef occur only in the tropical north, primarily along the Ningaloo coast, in the Kimberley, together with some in the Northern Territory and eastern Cape York Peninsula. The beaches consist of a usually steep, high tide reflective beach often composed of coarse coral fragments, fronted by the reef. The reef flats average 300 m in width but can range from 50-2000 m. On those reefs that grow to sea level, waves only reach the beach at high tide as they break across the reef flats, while at low tide, the reef is exposed and waves break on the reef edge.

Reflective plus rock/reef flats conceptual model shown at low tide exposing the hard rock flats or fringing coral reef. The outer edge of the rocks or reef often drops abruptly into deeper water.

Figure 26. Reflective plus rock/reef flats conceptual model shown at low tide exposing the hard rock flats or fringing coral reef. The outer edge of the rocks or reef often drops abruptly into deeper water.

A narrow high tide beach backed by laterite bluffs and fronted by irregular intertidal laterite (rock) flats at Charles Point, near Darwin, Northern Territory. (Photo: A D Short).

Figure 27. A narrow high tide beach backed by laterite bluffs and fronted by irregular intertidal laterite (rock) flats at Charles Point, near Darwin, Northern Territory. (Photo: A D Short).

Section of the fringing Ningaloo reef (Western Australia) showing the several hundred metre wide reef and backing narrow high tide beach. (Photo: A D Short).

Figure 28. Section of the fringing Ningaloo reef (Western Australia) showing the several hundred metre wide reef and backing narrow high tide beach. (Photo: A D Short).

Wave-dominated beaches | Tide-modified beaches | Tide-dominated beaches


Author

Andrew Short - University of Sydney

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