The discovery of fresh water underneath outback billabongs could impact Wild Rivers legislation and Water Resource Management plans, according to a leading water researcher.


Dr Jerry Maroulis, from the University of Southern Queensland,  is a member of an international team of researchers, led by ANSTO, who discovered fresh water lenses in saline groundwater along the Cooper Creek floodplain near Ballera in south-west Queensland.


Cooper Creek, which has the largest catchment area in the Lake Eyre basin, begins when the Thomson-Barcoo catchments combine to form an area known as the Channel Country.

Dr Maroulis said prior to this discovery, scientists believed floodwaters from this ancient floodplain largely evaporated or were absorbed into the many floodplain channels, waterholes and wetlands following a major flood event; what remained sometimes made it to Lake Eyre. Normally only 2-3 floods per century make it all the way from the Cooper through to Lake Eyre as it gets increasingly drier downstream.

'We realised the floodwaters were not becoming saline which would have been the case if evaporation was the key factor in reducing floodwater volumes downstream. So the question was, if it isn’t being evaporated then where is it going?'

Specifically the study identified that freshwater during low or no flow conditions had difficulty penetrating through the resistant clay-lined waterholes. However, during floods, there was enough energy to scour the beds of the waterholes and allow freshwater to enter the sandy and normally saline shallow sub-surface aquifer beneath.

'This subsurface water is critically important in sustaining the ecology during the ‘boom and bust’ cycles that characterise this area.

'This study provides the missing link in our understanding of the connectivity between flood hydrology and ecology,' said Dr Maroulis.

'We now know that the conservation of freshwater lenses are vital in supporting the vegetation along and near the channels of dryland river systems and contribute to sustaining the ecological balance of waterholes.

'Having now scientifically established this hydrological link, the question is how will this be factored into Wild Rivers legislation and Water Resource Management plans.'

Wild Rivers legislation prevents mining and irrigation in and around sensitive waterways, wetlands, lakes and waterholes.

Results from the study may also be applicable in other parts of the country.

'The study coincides with discoveries of similar lenses in the Murray River, but the Murray lenses are still within a predominantly gaining stream, whereas the Cooper Creek lenses are below the base of the waterholes Billabongs, and is therefore a hydrologically losing stream.

'The ground and surface water dynamics investigated may also provide a possible analogue for other Australian rivers that are expected to experience varied flow regimes under changing climatic conditions.'