Mapping Darling River groundwater from the air

Helicopters buzzing 100 metres above the ground have been crisscrossing the region around the Darling River above Wilcannia.

The Geo Australia choppers have an airborne electromagnetic survey instrument attached that sends waves down through the earth, which rebound back, measuring natural variations in the electrical properties of soil, rocks and water.

Project Leader of the Upper Darling Floodplain Study, Sam Buchanan, says, “it is a unique time to record the floodplain after the two flood events last summer.”

He explains the research will help better understand the effect of rain and flood on the alluvium water, which is below ground level.

The alluvium is the earth deposited by the river on the floodplains over millennia.

The Survey is recording the water content and types of ground up to 150 metres below the topsoil.

Mr Buchanan said the ground can change from silt, to clay, to sand and the rate of salinity from bores in this area also changes in relation to the ground it is around.

“We are trying to understand the relationship between groundwater and rain as well as the interaction of high saline water and low saline water in the alluvium,” he said.

The study will form the basis of an integrated understanding of surface water – groundwater interactions, groundwater quality and aquifer systems beneath the upper Darling River floodplain.

The study area covers about 31,000km2 and includes a 450km stretch of the Darling River floodplain from Wilcannia, upstream to Bourke and Brewarrina.

The upper Darling River floodplain is important for grazing and agriculture, both for regional NSW and for Australia.

It is hoped the study will identify new fresh groundwater resources beneath the upper Darling River floodplain, and discover potential places to store freshwater underground using Managed Aquifer

Recharge so as to provide ongoing and emergency supplies for towns and industries, improve the effectiveness of salt interception schemes, and understand how weirs affect groundwater resources.

The study methods include flying an airborne electromagnetic (AEM) survey, drilling new groundwater bores for monitoring, acquiring on-ground and downhole geophysics data such as magnetic resonance and electrical conductivity, as well as sampling groundwater bores for hydrochemistry, installing groundwater data loggers, and satellite analysis of water in the landscape with the help of

Digital Earth Australia and mapping the geology and aquifer systems.
All data produced by Geoscience Australia, including the data from this study, will be made publicly available after quality assurance has been performed at the Geoscience Australia Community and Education Portal.

Helicopter data is in and being analysed but some water measurements in places inaccessible due to floodwaters still need to be analysed.

The research findings will be available in the next two months.

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