Adelaide’s groundwater may be more susceptible to overuse than expected, researchers have warned, after an investigation into recharge mechanisms unearthed surprising results.
Flinders University researchers have published a paper establishing the origin of the city’s groundwater, which is ultimately fed by rainfall in the Mount Lofty Ranges.
Strategic professor of hydrogeology Okke Batelaan said they found Adelaide’s ability to meet its water requirements with groundwater was “more limited than thought”.
The paper’s lead author, Dr Etienne Bresciani, told ABC Radio Adelaide’s Afternoons program there were two mechanisms by which water from the ranges infiltrated the aquifer.
This included water absorbed into the hills before flowing laterally into the plains beneath the surface (mountain-block recharge), or water that flowed onto the plains via surface streams before leaking into or “infiltrating” the aquifer (mountain-front recharge).
“It’s really about finding out which of these two mechanisms were the dominant one for Adelaide, and, quite surprisingly, we found the stream infiltration was actually the dominant one in that case.
“This basically means we’ve probably overestimated the natural recharge of these aquifers, which meant this groundwater resource may be a bit more vulnerable to current and future extraction capacity.”
Adelaide’s groundwater is mainly fed via streams that run off the Mount Lofty Ranges. (ABC Radio Adelaide: Malcolm Sutton)
The dominance of the two mechanisms has long been debated due in part to difficulties understanding the hydraulic role of faults.
The research team used thousands of hydraulic head, chloride and electrical conductivity measurements to distinguish between the mechanisms.
Professor Bresciani warned that a year of strong rainfall did not necessarily improve the situation due to water taking a significant length of time to infiltrate the ground and reach the aquifers.
“The natural recharge that can happen even if there’s a bit more rainfall is not going to solve all the potential issues we have.”
He said groundwater levels in Adelaide had “significantly decreased” due to increasing extraction since the 1950s.
This water was mainly used for agricultural and industrial activities, he said, and “that included drinking products”.
Drilling for bore water has also increased among city residents, particularly during the water restrictions of last decade’s drought.
Many suburban gardeners put bore water signs in front yards to avoid being accused of gratuitous mains usage or to warn people against drinking it.
Water from high rainfall events should be captured, treated and injected into Adelaide’s aquifers, researchers say. (ABC: Spence Denny)
Professor Bresciani said their research emphasised a need to better manage groundwater and to focus on protecting and estimating the recharge qualities of streams and creeks.
But he said there was also relatively new technology surfacing that enabled manually recharging aquifers with run off, reclaimed or recycled water (once it was treated).
“These extra sources of water are usually lost to the ocean, but we can actually use it to artificially, in a managed way, recharge our aquifers.”
Trials in Salisbury and Bolivar had proved successful and should “inspire more of these facilities”, he said.
“This is definitely something that should be done more and more if we don’t want the groundwater levels to drop more than they’ve dropped so far.”
The research paper was published in the open-access journal Hydrology and Earth System Sciences.