Groundwater-surface water connectivity
Although it is not always apparent, surface water in many rivers, dams, lakes and wetlands is connected to underground water resources in aquifers. There are several different examples of these connections:
- groundwater can contribute to base flows in streams when it is discharged from aquifers.
- surface water can recharge groundwater resources when it seeps down into aquifers.
- extraction bores can affect surface water stream flows, even if they are tens of kilometres away from the stream.
This connectivity means that issues such as over-extraction, environmental flows and river salinity could impact on the water quantity and quality in both ground and surface water systems.
Managing connected systems
Traditionally groundwater and surface water have been managed separately in Australia. This has led to the same water being recorded twice - once in the groundwater management plan, and again in the surface water management plan. This has contributed to the overallocation of water resources.
Another difficulty in managing connected systems is that it takes some time for the effects of taking water from one system to be apparent in the other. While the impacts of groundwater extraction on stream flows can be virtually instantaneous in some systems, in others the impacts may take decades.
There's now concern that groundwater extractions over the past decades will result in reduced surface stream flows in some areas, although how much the flows will be reduced and how long this will take to occur is not clear.
An area of particular concern is the Murray-Darling Basin, where groundwater extractions have increased dramatically following the 1997 cap on surface water diversions.
Groundwater-surface water connectivity and water reform
Groundwater and surface water resources are intimately linked. Although we are still unclear as to the extent of these interconnections, they have important implications for management of both ground and surface water resources. It is critical that we build the knowledge and capacity needed to jointly manage these resources.
The National Water Initiative recognises the connectivity between surface and groundwater resources and requires connected systems to be managed as a single resource.
In 2007 in its Biennial Assessment of progress against the National Water Initiative, the National Water Commission found that there had been limited recognition in water plans of the connectivity between surface water and groundwater resources.
Although states had arrangements in place to manage groundwater, they did not amount to sophisticated, integrated management. This was put down to the complexity of the hydrology and a lack of knowledge of linkages and impacts.
The Commission concluded that significantly more effort needs to go into building knowledge of groundwater resources and the capacity to manage them.
Addressing groundwater quality issues
The National Groundwater Assessment Initiative under the Groundwater Action Plan provides for investment in managing risks to groundwater quality.