An artesian basin is a low-lying region where groundwater is cramped under pressure from surrounding layers of rock. These basins are usually found where an aquifer is present in a syncline, by impenetrable layers above as well as below. Whenever a fissure breaks the surface, the underground water blow up. This results in the rising of the water level to a point where hydrostatic equilibrium has been achieved.
A well drilled into this aquifer is known as an artesian well. If the water reaches the ground surface pressurized naturally by the aquifer, the well is known as a flowing artesian well. For an aquifer to be artesian, the water table must reach the surface.
The name artesian wells comes from the former province of Artois in France, where Carthusian monks had drilled many artesian wells.
The Great Artesian Basin (GAB)
The Great Artesian Basin is the largest and deepest artesian basin in the world. It is located within Australia, stretching over 1,700,000 square kilometres, and is huge enough to fill Sydney Harbour 130,000 times. The temperatures range from 30–100 °C. This artesian basin is the only dependable and safe source of fresh water for the rural communities. It holds 23% of the continent, and is 3,000 metres deep, consisting of 64,900 cubic kilometres of groundwater.
Geology of the Great Artesian Basin
During the Triassic, Jurassic, and early Cretaceous periods, the water of the GAB was retained in a sandstone layer placed by continental erosion of higher ground. Going back to the time when much of the present day inland Australia was below sea level, the sandstone was covered by a layer of marine sedimentary rock, which formed a confining layer, thus grasping water in the sandstone aquifer. When the Great Dividing Range developed, the eastern edge of the basin was elevated. The landforms of the Central Eastern Lowlands and the Great Western Plateau created the other side of the basin.
The recharge water mostly invades the rock formations from rather high ground near the eastern edge of the basin, and very steady flows towards the south and the west. A small quantity of water enters along the western margin in arid central Australia, which flows to the south and the east. As the sandstones are permeable, water moderately paves its way through the pores between the sand grains, and hence flowing at a rate of 1-5 meters per annum.