River conservation in Australia and New
|•||the Eastern Highland Belt consisting of a series of low mountain ranges, including the Great Dividing Range and Australia’s highest peak, Mt Kosciusko (2228 m);|
|•||the Central Eastern Lowlands with an altitude mostly below 150 m, including Lake Eyre at 14 m below sea level;|
|•||the Great Western Plateau covering most of the north and west with a relatively flat, uniform surface, giving way to incised valleys near the coast.|
New Zealand’s climate is largely marine-temperate, whereas Australia spans a range of climatic zones. The northern part of the continent is in the wet–dry tropics, the centre is semi-arid to arid, giving way to temperate and mediterranean climates in the south. The mean annual rainfall for the country is 465 mm, making it the driest of all of the permanently inhabited continents. Some 80% of the land has an annual rainfall <600 mm, whilst only 4% receives above 1200 mm yr-1. This low rainfall is exacerbated by high evaporative potential, with annual pan evaporation rates >2000 mm for most of the continent. The combination of low rainfall and high evaporation results in a meagre mean annual run-off of only 52 mm. Water is, therefore, a key limiting resource for human, economic and social development. Australia’s small human population of 18 million (ca 2 km-2; see Gopal et al., this volume, for contrast) is mostly concentrated in major urban areas around the relatively well-watered eastern coast.
New Zealand is much wetter and more mountainous than Australia. Mean annual rainfall ranges from 350 mm in central Otago, on the south-east of the South Island, to more than 12 000 mm yr-1 in the Southern Alps (Statistics New Zealand – SNZ, 1998). New Zealand is also much smaller in area (270 543 km2) and approximately half lies above 300 m AMSL, with slopes often greater than 28° (SNZ, 1998). Over 70% of the population (3.5 million – density 12.9 km-2) reside in the North Island.
The distinct climatic and geological regions of Australia give rise to a diversity of river types. The rivers draining east from the Eastern Highlands tend to be short, relatively high energy systems with steep headwaters in the range section, and meandering sections across the coastal plain. Those of the Central Eastern Lowlands are