Groundwater is an important resource in the Adelaide and the Mount Lofty Ranges region. It is used for irrigated horticulture, industrial applications such as beverage manufacture, linen washing and irrigation of recreational and sports fields throughout the metropolitan area.
What is groundwater?
Groundwater is the world’s largest source of fresh water. It is estimated that the amount of groundwater is 400 times greater than all the surface water in lakes, reservoirs, streams and rivers. Groundwater is part of the water cycle. When precipitation falls on land, some water evaporates, some flows into streams and some seeps into the soil and is absorbed by plant roots. Excess water in the soil may seep further down until it reaches a level known as the water table, where all the openings in the soil or rock are saturated with water. Water below the water table is called groundwater. Groundwater seeps slowly into low lying areas, streams, lakes, wetlands or the ocean, with about 40 per cent of the flow in Australian streams coming from groundwater. In turn, rivers and lakes can contribute large amounts of water to an aquifer as water seeps down into the soil, in a process called groundwater recharge.
Groundwater as a resource
Groundwater is an alternative to surface water supplies. It has many advantages. Groundwater is a vast resource with relatively constant chemistry and temperature and is free of micro-biological contaminants. Losses through evaporation are low and groundwater is buffered against climatic variability, especially drought. Groundwater can be tapped with a bore at the location where the water is needed. Some important issues related to groundwater use are over-extraction and groundwater quality. Once groundwater is polluted it is difficult to remedy.
Managing the use of groundwater
The use of groundwater must be carefully managed because while it is usually a renewable resource, its ability to replenish is limited. This is because groundwater moves very slowly, usually less than one metre per day. Groundwater systems have also established, over time, a balance between the rates of inflow (recharge), outflow (discharge) and the volume of water stored. Any new use of groundwater from a system will cause a change in this balance. Groundwater management aims to understand how these systems operate so water quality and quantity are maintained and use is sustainable into the future.
To ensure groundwater is used sustainably, some resources are protected by prescription and a water allocation plan that details how the resources are managed. These plans are developed by the Adelaide and Mount Lofty Ranges Natural Resources Management Board together with the local community. After the plan’s adoption, people using groundwater for commercial or large-scale purposes need to have a licence and take groundwater through an appropriate meter. There may also be other responsibilities such as sampling and reporting on the quality of water in their wells.
It is also important to consider that inappropriate waste disposal and land use activities can impact on groundwater because it sits beneath our urban and rural communities. There is a high risk from many pollutants as they can seep into groundwater, affecting its quality. These include sewage, effluent, heavy metals, petroleum fuels, solvents, herbicides, fertilisers, concentrated livestock excretion, nutrients, salt and detergents. Practices that adversely impact groundwater are regulated by the EPA to protect these resources.