Australia So Much to See

Underneath your feet lies one of the largest artesian groundwater basins in the world.  The Great Artesian Basin underlies about one fifth of Australia and extends beneath arid and semi arid regions of Queensland, New South Wales, South Australia and the Northern Territory.  The water supply here at Hamilton Hotel is drawn by wind power and comes from the basin deep below your feet. 

The aquifers of the Great Artesian Basin were formed between 100 and 250 million years ago and consist of alternating layers of water bearing (permeable) sandstone aquifers and non water bearing (impermeable) siltstones and mudstones.  The oldest waters from the basin have been dated up to two million years old (in the south western parts of the basin). 

The Basin covers a total area of over 1,711,000 square kilometres and it has an estimated total water storage of 64,900 million megalitres.

Recharge of the basin from rainfall occurs mainly along the eastern edges from the slopes of the Great Dividing Range.  Natural discharge occurs mainly from mound springs, which are natural outlets of the artesian aquifers where groundwater flows to the surface. 

The mound springs are used by Aboriginal people and some feature in Aboriginal myths and hold special spiritual significance. Mound springs are also a valuable resource which supports wildlife. 

Europeans first discovered the artesian groundwater of the Great Artesian Basin in 1878 when a shallow bore sunk near Bourke in New South Wales produced flowing water.  The first artesian flow in Queensland was obtained near Cunnamulla in 1887.  The opportunity of access to water proved invaluable for settlers, so more and more bores were sunk.  This provided reliable water supplies, allowing sheep and cattle to be raised on the vast Mitchell grass, Mulga and Spinifex plains. 

When bores were initially sunk to pull water from the basin in the early twentieth century, the rate at which water flowed out per bore was around ten megalitres per day.  However due to an increase in the number of bores and decrease in artesian pressure the water discharge rates have declined to between 0.01 – 0.06 megalitres per day. The total flow from the entire basin during the year 2000 was around 1,500 megalitres per day. 

Source: Queensland Government Department of Natural Resources and Water. 

Covering approximately 405,000 square kilometres, the Georgina Diamentina Catchment area is more than three times the size of England. 

It includes areas of the Northern Territory, Queensland and South Australia and is one of five catchments in the Lake Eyre Basin. 

The climate ranges from semi arid in the north and arid in the south and west. 

TheGeorgina and Diamentina rivers flood occasionally with short lived flows.  Floods travel slowly along the 1,000 kilometres of the Georgina from its source in the Northern Territory to Lake Eyre in South Australia. 

The Diamentina runs to Goyder Lagoon, 800 kilometres from its source.  Water can take months to travel down. 

The nature of these rivers cause them to disperse into multiple braided channels, floodplains and waterholes, known as the famed Channel Country of south west Queensland.

In times of high flow, Goyder Lagoon becomes a 1,300 square kilometre wetland that overflows 250 kilometres down the Warburton Creek into Lake Eyre, one of the world’s largest internally draining catchments. 

A 1.3 million square kilometre region in south western Queensland is known as Channel Country.  The name is derived from the network of riverbeds and streams coursing through the relatively flat terrain with erodible soils composed mostly of clay.  Channel Country is renowned for the braided channels and flood plains of the Diamentina, Thomson and Barcoo Rivers that become Eyre Creek and Cooper Creek further south. 

The weather patterns in this part of Queensland are highly variable and very seasonal. Winters (June to August) are generally dry and summers humid, featuring monsoon rains like the tropics.  When rain comes it is intermittent and often heavy, so the streams and creeks flow only in short bursts followed by long periods of drought.

Between flows, water collects in pools, billabongs and deeper channels that are a key element of the ecosystem.  Some are permanent. Waterholes are critical to the survival of a rich diversity of native wildlife and also support the grazing industry.  Channel Country supports more than fifty ecosystems including coolibah woodlands, sand plains and vast dunefields – all adapted to infrequent rainfall, massive deluges and a parching evaporation rate.    

The gentle gradient of Channel Country topography means that the floodwaters slow down, spreading out and break up into hundreds of small channels.  This process is referred to as anabranching.  When there is sufficient rainfall the channels fill up, overflow and cover the landscape.  Flood waters may not recede for several weeks.  Occasionally the rivers of the Channel Country drain into Lake Eyre, however most years they dry up through evaporation and absorption into the earth. 

A defining feature of Channel Country streams is their high turbidity.  This is due to sparse vegetation cover, a slow flow rate and the erodible clay soils. Turbidity is a measure of water clarity or murkiness.  During periods of high turbidity there is little light penetration into the water, therefore algal production is low, occurring only on the very margins of the channels, like a bath tub ring.

Survival of wildlife and plant communities here is dramatically influenced by the short, sharply defined times when water is plentiful.  Female kangaroos for example will produce young in rapid succession after rain.  At such times a female may have a young joey at heels as well as one in the pouch and a fertilised egg cell at an early stage of development.    

Read more about Understanding Channel Country

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