*Inside Cathedral Cave before COVID-19 restrictions (Photo: Bevin Liu)
Wellington Caves may be off-limits at the moment due to COVID-19 restrictions, but tourists aren’t the only ones keen to get back inside.
Researchers from the University of NSW have been studying water levels inside the underground complex in the hope of better understanding groundwater sources and how frequently they are replenished.
Cave and karst researcher Professor Andy Baker has been working at the site and surrounding areas since 2010. He believes the study can help communities and industry better manage groundwater use.
“The big science question and one of the reasons why I am doing this for research, is that we don’t know the relative importance of rainfall recharge versus river recharge,” Professor Baker said.
“If your livelihood depends upon rainfall recharge of the groundwater… understanding how frequently [that] recharge occurs… is really important. People can better manage what they are going to grow in the future [and] how they are going to manage their land.”
*Inside Cathedral Cave (Photos: Matthew Kruzmetra)
The initial part of the study looked at river recharge. It successfully identified the relationship between groundwater levels in the caves and water levels in the Bell River, which runs alongside the Wellington Caves complex.
Professor Baker believes it’s crucial that farming communities are educated about this relationship.
“I think groundwater as a whole is an education thing. It’s a government policy thing as well.”
“The government’s given [farmers] money to go and put new bores in, and that’s happening in the Central West of NSW,” he said. “Some of these bores might go into the groundwater resource, but [it’s] actually water that is being recharged by a river only a few hundred metres away.
“You’re not really helping the situation long term; you are actually taking more water indirectly out of the river system.”
(Voice of Professor Andy Baker, cave and karst researcher)
Gaden Cave was already closed before the coronavirus restrictions came into effect, because of a drought-induced build-up of carbon dioxide levels. The team of scientists, however, had been working in Cathedral Cave, Wellington’s largest show cave.
By placing automatic drip loggers at approximately thirty metres below the surface, they were able to monitor the amount of water seeping into the cave.
Professor Baker says that due to the severity of the drought, there was actually very little rainfall data to record – the last significant recharge dating back to 2016.
The recent drought led to other discoveries inside the cave.
“There is some graffiti down the bottom of the well from the Federation Drought of the 1890s, when early European explorers went down to the bottom of the cave.
“It hadn’t been this dry since then”.
*Markings written by caves explorers during the long Federal Drought 1895-1903 (Photos: Supplied, Michelle Tonkins)
Rising temperatures are also continuing to have a greater impact on groundwater recharge due to an increase in evaporation from the soil and rivers.
This is particularly problematic for communities that rely on rainfall to recharge their groundwater stores.
“If you can conceptualise your soil as a store of water and evaporation is higher because it is getting warmer… there is going to be less moisture in the soil. And, every time it rains, that rain is actually used to top up the water store in the soil and doesn’t go into the groundwater”, he explains.
“It might be okay for farming if your roots just use the shallow soil water, but for groundwater recharge, long-term sustainability could get worse.
Professor Baker says it is extremely difficult to estimate just how long communities can continue to use groundwater at their current rates, but this uncertainty surrounding sustainable groundwater use is what makes the team’s research so important.
“The short-term solution is to put the bore in the alluvial gravels and [have enough] to last the next few years until the rivers are flowing… enough that it’s not a problem.”
Data collection is still happening automatically during the cave’s closure. Now that significant rain has fallen, Professor Baker says he is excited to see how much recharge has occurred.
— Story, interview and photos, Bevin Liu and William Owens
*This story has also appeared in Dubbo’s The Daily Liberal