Groundwater is something we rarely think about because it is hidden underground in the spaces between grains of sediment and rock. However, groundwater is extremely important to Australia, supplying water for drinking, agriculture and the environment.
Aqui-terminology
There are several specialised
terms to know when studying groundwater. An aquifer is a connected area
of sediment and/or rock that can hold water. Australia’s largest aquifer is the
Great Artesian Basin. This extensive aquifer covers 20% of Australia’s land
surface and is estimated to hold 65 000 million megalitres of water. That
volume of water could fill 130 000 Sydney Harbours!
An aquifer that has no barrier
above it can discharge into streams and recharge from rainwater. This is an unconfined
aquifer. Aquifers that have water-resistant layers above and below them are
known as confined aquifers.
Groundwater may be confined by an aquiclude
that does not allow any water movement (shown in brown in the diagram below).
An aquitard is a layer that acts as a barrier but allows some water to
seep through (shown in dark blue in the diagram below).
Uses of Groundwater
In many areas of Australia,
groundwater is the only reliable source of fresh water for people and livestock.
Approximately two-thirds of the drinking water in Western Australia is sourced
from groundwater. Groundwater may be bottled for direct use or used by beverage
manufacturers to make soft drinks and beer.
People do not just drink groundwater.
About half of the groundwater use in Australia is for irrigating crops,
allowing us to grow food when rainfall is scarce and unpredictable. Many mining
operations in arid areas are entirely dependent upon groundwater for their
people and industrial uses such as dust control and mineral extraction.
Groundwater supplies unique spring and wetland ecosystems and is a major determinant of stream flow in some areas. Many plants and animals depend upon groundwater for their survival. Understanding the connections between groundwater, wetlands and rivers is the subject of ongoing investigation and monitoring by the CSIRO, Geoscience Australia, Bureau of Meteorology and other agencies. These models are vital for sustainable groundwater use.
Human Impacts on Groundwater
In coastal areas of Australia,
seawater may flow into aquifers and seep inland as natural groundwater
discharge is stopped or reversed by use of bores. Contaminants such as
gasoline, oil, pesticides and industrial chemicals can migrate into aquifers
and move large distances below the surface.
Overuse of groundwater has many
potential impacts. Ecosystems dependent on groundwater are placed at risk. This
includes 98 endemic species in the Great Artesian Basin region. Removing
groundwater may cause subsidence and collapse of overlying land. The San
Joaquin Valley in California has sunk more than 8 metres in the past 100 years
due to overextraction of groundwater.
Climate change naturally impacts on groundwater levels and increased human use of groundwater can magnify the effect. Greater evapotranspiration and increased pumping for human use lower groundwater more quickly in times of drought. Thus, groundwater use is seen as a temporary measure in many cities to be used only during drought, allowing aquifers to replenish during times of higher rainfall.
Explore
- Make yourself a groundwater spider and carry out a tasty investigation of confined and unconfined aquifers. This AusEarthEd video visualises groundwater contamination using the groundwater spider model.
- See how much water is contained in each of Earth’s water stores in our video Representing Earth’s Water.
- Geoscience Australia has a section of resources about groundwater and the Bureau of Meteorology provides many different types of information about groundwater resources.
- Read about the importance of groundwater and our impact on it in Forbes magazine.