Demand for groundwater has increased as access to surface water supplies has become constrained. Groundwater resources are now being managed through water sharing plans for sustainable long-term usage.
Groundwater is generally seen as a supplementary water resource. However, for many communities in regional NSW, groundwater is the primary source of water for drinking, stock and domestic use, agriculture and other industries. Importantly, too, a range of ecosystems depend on groundwater for their continued survival, including some surface water bodies (wetlands, rivers and lakes) that are connected to groundwater, as well as some terrestrial ecosystems. Significant changes in groundwater quality and quantity have the potential to degrade ecosystems and affect human uses of water. Because of the hidden nature of many groundwater dependent ecosystems, the impacts are likely to be less obvious and well-understood.
Major Uses of Groundwater
Approximately 11% of the water used in NSW comes from groundwater sources. Agriculture and mining are the largest users of groundwater in NSW, with the greatest volume used for irrigation in areas around the main inland alluvial aquifers. For some inland mining operations, groundwater is the only available source of water, but it may also be an obstruction or hazard that must be removed before mining can proceed. For more than 200 towns in NSW, groundwater is the principal source of water supply. An estimated 13% of the groundwater used in NSW goes to domestic and stock purposes.
Levels of Extraction and Recharge
Variability in climatic conditions affects the amount of groundwater used. Extraction may increase substantially in times of drought to offset the lack of surface water, while in periods of high rainfall, groundwater will be recharged more and used less. Due to the heavy competition for surface water supplies in NSW, demand for groundwater resources has generally increased over the past 10 years. Extraction peaked at around 1300 GL in 2002–03, but extraction levels are highly variable from year to year. Typically extraction has generally been between 500 and 1000 GL per year.
Long-term Average Extraction Limits
The intent of water sharing plans for groundwater is to manage the resource sustainably so that extraction remains in balance with yield over the longer term. This means that over-extraction in times of drought, is permissible, providing that extraction drops back below the sustainable yield after the period of drought to allow water levels to recover. This natural flexibility of groundwater systems provides for a reliable and secure water resource. The long-term average extraction limit is the level of groundwater that can be extracted sustainably on an annual basis. At the state scale the overall level of entitlement compared with the long-term average extraction limit is quite low, at around 20%.
Groundwater Dependent Ecosystems
‘Groundwater dependent ecosystems’ are those that rely in whole or in part, particularly during drought, for their survival on groundwater.
Terrestrial vegetation may depend on diffuse discharges of shallow groundwater to varying degrees, either to sustain transpiration and growth through a dry season or to maintain perennially lush ecosystems in otherwise arid environments.
Wetland ecosystems may depend on groundwater to keep them seasonally waterlogged or flooded. Wetlands provide the most extensive and diverse set of potentially groundwater dependent ecosystems in Australia.
River baseflow systems rely on groundwater for the character and composition of in-stream and near-stream ecosystems.
Aquifer and cave ecosystems are heavily dependent on groundwater for life forms that live in their porous and fissured aquifers. Life in cave aquifers may be as rich as it is above ground.
Terrestrial fauna rely on groundwater as a source of drinking water. Groundwater, as river baseflow or discharge into a spring or pool, is an important source of water across much of the country, particularly in northern and inland Australia and other areas with a semi-arid climate. Its significance is greater for larger mammals and birds, as many smaller animals can obtain most of their water requirements from their food or respiration.
Pastoralists in inland Australia have made extensive use of groundwater to supply drinking water to grazing stock. In addition to watering stock, groundwater is also used by native fauna, such as kangaroos, and pest and feral animals. Provision of water has allowed larger populations of both wildlife and pest animals to be sustained than would otherwise be the case.
Estuarine and near-shore marine systems which may depend on groundwater discharges to provide a suitable habitat include coastal lakes, mangroves, saltmarshes and seagrass beds. Groundwater discharge may be in the form of direct off-shore discharge or baseflow into streams that discharge to the ocean.
Department of Environment, Climate Change and Water