Coast, coastal zone

The term ‘coast’ or ‘coastline’ have different meanings for different purposes.

The Macquarie dictionary defines ‘coast’ as the land next to the sea. The ‘coast’ has also been defined as a strip of land of indefinite width that extends inland from the shore to the first change in terrain that is unaffected by marine processes [1], and the land adjacent to the sea upon which waves have an effect [2].

Coast could therefore include bays, inlets and estuaries. The extent that the term coast applies inland can be debated. Options include the various tide heights, the maximum extent of inundation (extent of storm surges etc), the limit of tidal influence on rivers and estuaries, the limit of salt water, and the extent of coastal vegetation.

The extent that the term ‘coast’ applies offshore is also unclear. Options include the line of lowest astronomical tide, the territorial sea baseline, limit of islands and reefs, continental shelf, etc.

Legally there are also variations on what constitutes the coast. For example, most property boundaries adjoining the coast are limited to the ‘high water mark’ or 30 metres landward of the high water mark. The limits of each State (and the Northern Territory) are generally the line of ‘low water mark’. The term ‘low water’ also has different meanings in different States. A working group of the Intergovernmental Committee on Surveying and Mapping (ICSM) has identified over 50 different terms relating to the coastline used in Commonwealth and State legislation.

For the purposes of OzCoast and OzEstuaries, we have defined the ‘coast’ broadly to include areas of related to the coastal environment. OzCoast and OzEstuaries is primarily concerned with estuaries and the broadest limits of the inter-tidal zone. In some cases OzCoast and OzEstuaries covers areas further offshore where environmental studies provide information relevant to coastal management i.e. to the 3 nautical miles offshore (coastal waters) and coastal IMCRA regions.

  1. Duxbury, A. C. and A. B. Duxbury (1991). An Introduction to the Worlds Oceans. Dubuque, Indiana, W C Brown.
  2. Watt, A. (1982). Longman Illustrated Dictionary of Geology. Harlow, Essex, England, Longman Group: 192 pp.

More information on marine & costal maritime boundaries


Bill Hirst
Peter Harris

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