Mathematics to help understand flows on unique mound springs

The Great Artesian Basin’s unique mound springs are in danger. A new mathematical model might help by looking at the effects of reduced water extraction on the mounds.

Mound springs are unique, an environmental asset of international significance, with historic and ongoing cultural and economic value. But they are usually located in arid, inhospitable outback regions where you need to be a fairly intrepid person to reach them.

For example, heritage-listed Witjira-Dalhousie Springs in South Australia’s far north is only 70km from the nearest food and supplies at remote Mt Dare station on the fringe of the Simpson Desert.

Only four wheel drives can travel from the famous Mt Dare pub to the springs, via a heavily rutted, usually corrugated and sometimes washed out track. Dalhousie’s flow of artesian freshwater is about 14 million litres a day, but it’s a must-do swimming and camping spot for off-road tourists.

Although it appears to be little more than a pool in a wide clay pan, it’s  a mound spring; the biggest of its ponds is 60m wide, more than 160m long, and reaches almost 12m deep.

Experts say there are 5000 such watery features in SA’s north. Not all are as big as Dalhousie. But regardless of size, these mound springs are in danger.

Since European colonisation, flows from about a third of Outback springs have declined.

Development and modern land use have taken a toll, including from an estimated 50,000 constructed bores. And more than 1000 springs have dried up altogether.

A warming climate also figures prominently, with some scientists arguing for conservation of the springs to provide a stable hydrologic refuge for the future.

Recent research reveals the groundwater itself to be a global keystone ecosystem, one often overlooked in conservation agendas.

What are mound springs?

Mound springs are the intermittent surface expression of Australia’s Great Artesian Basin (GAB), a deep regional groundwater system covering 22% of the continent and the largest underground freshwater reserve in the world.

Scattered around the edges of the GAB’s 1.7 million sq km are 12 “supergroups” of springs.

Experts estimate some 7000 individual springs arranged in 450 springs groups help quench parched patches of the Northern Territory, Queensland, South Australia, and New South Wales.

Mound springs are defined as the “accumulations of predominantly calcium carbonate (CaCO3) in dome or shield-like structures around the vent of a spring.” Springwater first emerges into a pool located at the summit of the mound … while the discharge zone that forms a wetland at the base of the mound, is called a spring tail.

Lost ark of animals – the mound spring

For thousands of years, such freshwater oases helped Aboriginal traders ply their routes between the red centre and Australia’s south.

From the 1850s, European explorers noted “bright green mounds rising out of a saltpan”, the knowledge enabling Scottish surveyor John McDouall Stuart to visit Central Australia in 1860 and become the first European to cross the continent from the south to its northern tip in 1862.

Economically, water sourced from the GAB returns some $13 billion of production annually, via stock, mining, gas and tourism. Yet significant impacts also arise, through agribusiness, the food and wine industry and the energy and mining sectors, as well as degradation by cattle and feral herbivores.

What is being done?

In December, the Goyder Institute for Water Research announced it plans to mathematically model the effects on springs of reducing the amount of water extracted from GAB aquifers.

Project scientists will use a GAB hydrogeological computer model developed by the SA Department of Environment and Water, which has partnered with Flinders University for the work.

In a statement, the Goyder Institute says: “The project aims to improve the model regarding the relationship between volume of water held within the GAB, the response of aquifer pressure, and the impact on mound springs within Northern South Australia.”

The Institute says it will investigate how spring pressure levels and flow rates from spring tails behave if extraction from GAB aquifers is reduced, using “predictive scenario analysis”, a sort of mathematical “what-if” method.

The project is funded by Infrastructure SA.

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