Blue Lake supplies city of Mount Gambier with rest of South Australia's southeast region also relying on groundwater
Along with the city of Mount Gambier, getting its water from the Blue Lake, the whole South Australian southeast region relied on groundwater. Use of that water was regulated and monitored as part of the Lower Limestone Coast Prescribed Wells Area (with green boundary on inset map) with the Donovans, MacDonnell and Kongorong water management areas. along the coast.
Images courtesy SA Water and Water Connect
Mount Gambier, the biggest city in South Australia’s southeast, had its water supplied from the Blue Lake, one of the groundwater sources relied on by that whole region of the state.
The Blue Lake – South Australia’s third largest water storage – was a volcanic crater where groundwater seeped in through porous limestone to create around 36,000 megalitres of water. About 10% of that was used each year by Mount Gambier. South Australian government-owned utility SA Water, with a licence to extract a maximum four gigalitres of water from the lake each year, said in the early 2020s that the lake had at least 30 years' worth of water supply for Mount Gambier residents.
The whole southeast area south of Mount Gambier, covering 13,300 square kilometres, was in the Lower Limestone Coast Prescribed Wells Area, meaning its use of groundwater was regulated under South Australia’s Natural Resources Management Act 2004. Plans for allocating water in three areas – the Comaum-Caroline, Lacepede Kongorong and Naracoorte Ranges Plans – aimed to provide sustainable water management for the region.
Pasture was the dominant irrigated crop in the area, taking about 61% of the total licensed volume of water. Lucerne accounted for 13% of water for irrigation, with potatoes 8% and vines 7%. Plantation forests impacted groundwater resource particularly where the watertable was shallow. But the most widespread influence on groundwater levels reduced recharge around the early 2020s was due to drier rainfall conditions.
Also south of Mount Gambier, coastal groundwater management areas of Donovans, MacDonnell and Kongorong, along 65 kilomteres stretch of South Australian coast, were home to multiple environmental, social and economic assets, all depending upon groundwater. Within these areas were 9,200 hectares of commercial forests, irrigated dairy agriculture with groundwater extraction ranging from 28 to 51 gigalitres per year and the Ramsar-listed Piccaninnie Ponds karst wetland.
Several other karst springs and wetlands were present along the coastal strip with the region referred to as the Karst springs and associated alkaline fens of the Naracoorte coastal plain bioregion. They were listed as critically endangered under the Commonwealth Environment Protection Biodiversity Conservation Act 1999. Many karst springs were also important tourist destinations for the region.
In the Donovans Management Area, declines in water level increased the risk of sea water intrusion. Salinity trends in the confined aquifer throughout the Lower Limestone Coast Prescribed Wells Area were stable.
The Groundwater (Border Agreement) Act 1985 was for groundwater in the section near the border of South Australia and Victoria to be shared equally between the states.
