Gilbert-Einasleigh River

Infobox River
river_name = Gilbert-Einasleigh River
origin = in Einasleigh Uplands, north of Hughenden
mouth = Gulf of Carpentaria
basin_countries = Australia
length = 610 km (379 mi)
elevation = 800m (2600 ft) at source
discharge = 350 m³/s (river extremely seasonal)
watershed = 46,810 km²

The Gilbert-Einasleigh River is one of the largest river systems in northern Australia. It is located in north-central Queensland, between the Flinders River and the Mitchell River. Although it is a seasonal stream and discharge can vary greatly depending on the intensity of the monsoon, the Gilbert-Einasleigh has the sixth-highest discharge of any river in Australia, about equal to that of the Potomac in North America. In a very wet "wet" season, however, the discharge can be as large as that of the Fraser River in Canada, and in a dry "wet" like that of 1951/1952, the discharge can be as little as "one tenth" the long term mean. It is estimated that runoff from the Gilbert-Einasleigh system totals about 2.2 percent of the total runoff from Australia [Brown, John Alexander Henstridge; Australia’s Surface Water Resources; published 1983 by Australian Government Publication Service, Canberra] .

Both the Gilbert and Einasleigh Rivers rise in ancient uplands to the west of the Atherton Tableland in northern Queensland. The two streams have their sources very close to each other but they begin by diverging as they flow into lower-lying country to the west, the Gilbert anticlockwise and the Einasleigh clockwise. Their almost circular flow takes them eventually together where they join almost due east of Normanton and then flow in a west-northwesterly direction to the Gulf of Carpentaria. The only major tributary is the Etheridge River which joins the two main stems at a point very close to their convergence. From this point on, the river flows into a vast estuarine delta that largely consists of tidal flats and mangrove swamps which flood during the "wet" season.

The climate of the basin is tropical, with annual rainfall generally around 800mm (31-32 inches). Almost all the annual rainfall occurs between December and March: the months from May to September are rainless in over 60 percent of years (over 80 percent for August). Rainfall is highly variable due to monsoon variability and occasional severe cyclones: in a wet season like 1973/1974 or 1999/2000 it can exceed 1800mm (70 inches), but in the almost nonexistent wet season of 1951/1952 it was as low as 300mm (12 inches) over much of the basin.

Because the river is much too erratic for hydroelectricity to be viable and the soils are exceedingly infertile - generally ironstone gravels or kaolinitic clays - the Gilbert-Einasleigh is one of the relatively few completely free-flowing river systems of its size or greater in the world. Most of the basin is natural grassland used for grazing cattle at the extremely low densities permissible with the very low nutritive qualities of the feed available: the population is no more than one thousand or one person for over 40 square kilometres. In the upper reaches soils are more fertile red cracking clays but erode too easily under the erratic rainfall for cropping to be a likely prospect even with groundwater available.

Notes

* [http://www.bom.gov.au/hydro/flood/qld/brochures/gilbert/map.shtml Gilbert]