Mysteries of Bordertown's Poocher Swamp uncovered

07-06-2017

Mysteries of Bordertown's Poocher Swamp uncovered

A $500,000, six-year study into Poocher Swamp and the limestone aquifers it supplies has given SA Water a unique understanding of how Bordertown’s fresh water source refills.

The research was the largest study ever conducted into Poocher Swamp’s groundwater system, and confirmed the size of the aquifer and how it can provide Bordertown residents with a sustainable supply of drinking water.

SA Water’s Water Security Planning Manager, Glyn Ashman said the aquifer is a precious resource for Bordertown, and an inspiring feature of the natural environment.

“The Poocher Swamp aquifer network is an oasis of fresh groundwater surrounded by brackish water,” Glyn said.

“These new findings on the aquifer’s size and the limestone cavity networks will help us operate the borefield and plan the long-term security of Bordertown’s water supply, safeguarding it for future generations to enjoy.”

Bordertown relies on a groundwater supply refilled by water draining through runaway holes in Poocher Swamp and flowing through a hidden, underground network of limestone cavities leading into the aquifer.

The extensive study also assessed how the flows from Tatiara Creek into Poocher Swamp impact both the security and quality of the underground supply.

Bacteria and other microbes in the raw water bond to limestone particles and are removed from the water as it flows through the porous rock, allowing the aquifers to act as a natural filter.

“The limestone aquifers are a highly effective natural filter and compliment the treatment processes that SA Water follows to ensure our Bordertown customers receive high-quality, clean and safe water from the area’s bores,” Glyn said.

SA Water worked with local landowners and was assisted by Department of Environment and Natural Resources and specialist geophysical contractors to complete the research into the groundwater resource.

During the study, SA Water and its partners accessed local land to drill monitoring bores, establish flow gauging stations, collect water samples and conduct electromagnetic surveys to locate groundwater.

Researchers used a technique called NanoTEM, which sends an electromagnetic pulse into the ground and records the signals that bounce back. Comparing signals from the ground with data collected on rock formations in boreholes allowed SA Water to build up a detailed picture of the underground water system.

“Having the cooperation of landholders enabled us to map Poocher Swamp’s underground freshwater aquifer network.

“We had an unprecedented opportunity to monitor, measure and understand how water moves through the swamp into the runaway holes, and where it travels to recharge the aquifer,” Glyn said.

Another new insight obtained during the project was that the aquifer recharged at a rate of 18 million litres per day when the swamp flooded in 2016, leading to new theories about why the swamp drains so rapidly.

“Water drains through the runaway holes at the bottom of the swamp very quickly, and is known to make a noise like a jet engine.

“One of the theories is this is caused by air being trapped underground as the aquifer starts to recharge.

“Once the flow of water underground starts to slow, the pressure changes and air escapes, rushing out and allowing water from the runaway holes to rapidly gush down and fill the void.

“Air whooshing out of the aquifer may account for the mysterious loud noise reported by locals when the swamp is draining,” Glyn said.

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