Why They Are There
Water infiltrates into the ground to become groundwater. It flows slowly through porous rock or sand (aquifer), under the influence of gravity . It eventually discharges to the surface lower in the landscape via springs. Springs occur where there is a pathway for the water to escape and where the watertable (or groundwater pressure) is above ground level.
Mechanisms for the Formation of Springs
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The Distribution and properties of springs are determined by several factors including:
Topography | Rainfall | Aquifer Type
Topography
In order for groundwater to flow and therefore to discharge as springs, the watertable in the recharge area must be higher than that in the area where it discharges. The more relief an area has, the more potential there is for groundwater to flow and thus to emerge as springs.
Although the Northern Territory is relatively flat, the north flowing rivers that drain to the sea have dissected an ancient landscape. This can be seen as a zone with moderate relief extending in from the coast for some 200km. The majority of springs are located within this zone.
Inland from there, the generally flat landscape combined with low rainfall (and thus low groundwater recharge) limits the occurrence of springs.An exception is the Central Australian Ranges in the southern part of the Territory where a series of rugged ranges results in numerous springs. Low rainfall restricts them to minor features with very small flows.
Rainfall
Most of the springs are located in the higher rainfall areas of the north (generally above 600mm/year). The higher the rainfall the longer springs tend to flow through the Dry season.
Aquifer Type
Major Aquifers
Both carbonate rocks and sandstone form widespread aquifers that have large storage capacities and the ability to transmit water relatively rapidly.Spring flows tend to be relatively high and long lasting in these aquifers. The former tend to form localised springs because discrete caves and fractures transmit the groundwater. Example
The sandstone aquifers on the other hand are more homogeneous and discharge occurs as streambed seepage. Example
Few springs occur in the major aquifers in the southern two thirds of the Territory due to the low topographic relief and arid climate.
Minor Aquifers
Local fractured rock aquifers underlie the remaining areas. These also support many springs but they tend to have smaller flows and they generally dry up before the end of the Dry season. Example
