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Estimated Areas of Wetlands in the Australian Coastal Zone

NH Wood and KD Cocks
CSIRO, 1994

The Coastal and Marine Resources Information System, CAMRIS, is a geographic analysis system developed to help with small scale decisions involving the use of Australia's coastal resources (Hamilton and Cocks 1993). Bio-physical and socio-economic resource data in CAMRIS is spatially referenced to several different sets of spatial units including 3027 sections each approximately 10 km by 3 km (Galloway et al 1984) collectively covering the whole of the Australian coast.

This working document presents estimates in List 1 of the areas in sq km of 16 broad classes of wetlands for the whole of coastal Australia and also for each state and the Northern Territory. The same data is presented in percentage form in List 2 (Percentage contribution of each wetland categories to each state's area of wetland) and List 3 (Percentage contribution by state to the national area of each wetland category). The coastal zone is defined here by the inland section boundaries of Galloway et al (1984). The 16 classes of wetlands have been aggregated from 31 of the original 43 classes of wetlands presented in Paijmans et al (1985), and listed in Wood and Cocks (1990).

In Paijmans et al, land temporarily or permanently under water or waterlogged is classified as wetland. Their data covers fresh and salt water versions (where applicable) of five of the six major categories of wetlands, namely lakes (perennial, man-made, intermittent and episodic/dry ), swamps (perennial, and intermittent), land subject to inundation, tidal flats and mangroves, coastal inshore water bodies (open lagoons/ estuaries/ tidal rivers and waterholes). No separate data is available for the sixth type of wetlands, rivers and creeks; estimates of these are included in coastal water bodies .

Methods

For the present document, wetland occurrences have been estimated as either feature counts or areas per section; counts are used for smaller-sized occurrences of features and areas for larger features. The estimates were made by overlaying each 1:250 000 topographic map marked with the coastal section boundaries with both the corresponding transparency of marked wetlands from the original wetlands study (Paijmans et al 1985) and with another transparency of grids approximating 3 sq km. Within each section, the count is the number of occurrences of smaller wetland types (less than 20 mm in diameter on 1:250 000 map ) whilst the area of the larger wetlands (those greater than 20 mm ) is estimated as an integer value in gridcell-units of 3 sq km.

In the Paijmans et al study, the average size of a small wetland occurrence was assumed to be 10 mm in diameter at 1:250 000 scale which translates to approximately 5 sq km. (i.e. 3.14*1.25**2 sq km ). However, the area of waterholes (but not other small wetlands) is probably overestimated using the average area of a count as 5 sq km, so for the present set of estimates the average size of a waterhole is taken as 1 sq km.

Many small wetlands do not appear on the Paijmans et al overlay maps because they do not meet the minimum size specification of 6 ha (1mm diameter on the 1:250 000 map; p3, Paijmans Explanatory Notes in Wood and Cocks, 1990). The waterholes category includes, as well as waterholes, lakes less than 1 km in diameter (4 mm on the map), and wide stretches of river less than 5 km long (p2, Paijmans Explanatory Notes). All wetlands less than 1 km across are termed waterholes ( p45 Paijmans et al 1985). Consequently, small mangrove areas and swamps are categorised as waterholes, ie, the heading 'waterholes' is short for 'waterholes and other small wetlands'.

The total area for each of 16 different classes of wetlands is calculated by summing for each wetland type the estimated areas for the larger occurrences and [counts multiplied by a standard area] for smaller occurrences.

The minor inconsistencies in adjoining map sheets referred to in the Paijmans Explanatory Notes for Mapping (p3, in Wood and Cocks (1990)) were evident on reworking the coastal sheets; a lake changed from fresh on the Collie map to salt on the Pinjarra map and an intermittent swamp on the Dampier map became a tidal flat on the Roebourne map; a perennial salt swamp on the Roper River map became a tidal flat on the Mt Young map.

Comments

This document is essentially a data record and is not the place to discuss the implications of the estimates it contains. Nevertheless, several observations are in order.

The coastal zone, as defined here is 42% wetlands. This definition while nominally identifying a 3 km strip adjoining marine waters frequently extends inland to circumscribe Holocene features which are also categories of wetlands. Thus this surprisingly high figure is partly due to the inclusion, as wetlands and as part of the terrestrial coastal zone, of very large areas of mangroves and tidal flats, mostly in northern Australia. In fact, the fraction of the coastal zone occupied by wetlands varies from 64% in Northern Territory to 14% in Tasmania.

Open lagoons and estuaries contribute the bulk of Tasmania's (82%) and New South Wales' (61%) coastal wetlands. Victoria's coastal wetlands (26% of the Victorian coastal zone) are a more balanced mixture of perennial and periodic salt and fresh lakes and swamps. While wetland areas are presented in the present document by State and nationally, aggregation from sections to other regional bases such as drainage divisions would be equally possible.

The present publication does not categorise wetlands in terms of their ecological quality or importance. The conservation status of Australian wetlands is discussed at length in McComb and Lake (1988). More recently, a publication by Australian Nature Conservation Agency (Usback and James 1993) identifies, Australia-wide, 520 wetlands recognised as important by state authorities. Of these 161 are classified as 'Coastal and marine'.

References

Usback, S., and James, R., (eds) (1993) A directory of important wetlands in Australia, Australian Nature Conservation Agency, Canberra.

Hamilton, N.T.M. and Cocks, K.D. (1993) A small scale geographic analysis system for maritime Australia. CSIRO Division of Wildlife and Ecology Working Document 93/9.

Galloway, R.W., Story, R., Cooper, R. and Yapp, G.A. (1984) Coastal Lands of Australia. CSIRO Division of Water and Land Resources, Natural Resource Series No. 1.

McComb, A.J. and Lake, P.S., (1988), Conservation of Australian wetlands, Surrey Beatty, Chipping Norton, New South Wales.

Paijmans, K., Galloway, R.W., Faith, D.P., Fleming, P.M., Haantjens, H.A., Heyligers, P.C., Kalma, J.D. and Loffler, E. (1985) Aspects of Australian wetlands. CSIRO Division of Water and Land Resources Technical Paper No. 44.

Wood, N.H. and Cocks, K.D. (1990) Distribution of Wetlands in Australia - Current status of dataset and maps. CSIRO Division of Wildlife and Ecology Working Document 90/2.