Deep water: health of the Great Artesian Basin

Glen Paul: G’day, and welcome to CSIROpod. I’m Glen Paul. The Great Artesian Basin, or GAB as it’s sometimes called, is one of the largest artesian groundwater basins in the world, underlying parts of Queensland, New South Wales, South Australia, and the Northern Territory. With rural Australia so reliant on it, and each State and Territory having different legislative frameworks for its use, a coordinated whole of basin approach to the management is necessary.

The last comprehensive study of the basin took place in 1980, and with an increasing demand to understand the hydrology of the GAB water, CSIRO in collaboration with Geoscience Australia has recently completed a 2½ year A$6.25 million project to assess water resources in the Great Artesian Basin.

Joining me on the line to discuss findings is CSIRO’s Doctor Brian Smerdon. Brian, just how difficult is it to assess an underground water store that’s big enough to fill Sydney Harbour 130,000 times?

Dr Smerdon: Yes, it’s quite a challenge actually. I mean compared to surface water catchments where you can actually see where water’s draining, the groundwater systems that we typically work in are much more difficult to visualise, and that definitely adds some complexity in trying to see what’s going on and assess the water resource.

Glen Paul: Right. So just to get a handle on it, how did the Great Artesian Basin form, and is it just essentially a giant underground water tank, or is it more complex than that?

Dr Smerdon: Yes, probably no surprise, it’s much more complex than that. It’s a geological feature basically that’s evolved of course through geological time, so if you trace your way back through the Jurassic period and the Cretaceous period, and even earlier, that’s when the sediments were laid and that actually formed the layers that are the aquifers that are the Great Artesian Basin.

So you’re talking, you know, millions of years of geological evolution, shaping, moulding, faulting, twisting and bending, eventually actually it all gets sort of uplifted and pushed upwards, and that’s why it’s become artesian, the condition we see today.

Glen Paul: OK. And it’s been providing the only reliable source of freshwater for inland Australia since the first bore holes were sunk in the 19^th Century, so why the renewed interest?

Dr Smerdon: I guess there’s always been interest from, like even from the 1800s, starting from those first bores, or even earlier, when there would have been springs feeding populations before that. The renewed interest now is building on a lot of the resources being I guess mined or extracted in different parts of Australia, and of course the GAB covering a large portion of Australia you’ve got an interaction of coal seam gas, or coal deposits, or just the water itself, and really tying it all together and understanding how the GAB works is the big question.

Glen Paul: OK. So there’s obviously interest then from the mining industry. How much significance will the report have on that industry and its development?

Dr Smerdon: What we’ve really done is actually just pull together our geological knowledge, hydro geological knowledge, like you say probably since that 1980 report there’s been lots of different scientific studies, and this is really the first one that draws it all together in a consistent way across the whole GAB. So what we’re really leaving as a legacy is a package of information that both Governments and perhaps mining companies themselves can actually use. So the implications are really to better understand the current condition, and some of the future conditions, based on different aspects of climate or extraction, and that’s what we’re really leaving at the end of this project.

Glen Paul: And obviously agriculture would have great interest in this report. And as someone who worked on a cattle station in their youth, I recall clearing bore drains with a tractor to allow this seemingly endless supply of water to flow across the property, but even then I would ponder what would happen if the well were to run dry. Is there sufficient water going in to replace what’s coming out?

Dr Smerdon: Yeah, we’ve got… as it’s a geological feature, some parts of the Basin, for example on the western side of the GAB, the rates of replenishment are actually quite low nowadays, compared to thousands of years ago when there would have been much wetter conditions feeding the aquifers of the GAB. It’s a little different on the eastern side of the GAB. We still have quite a bit of recharge coming in from the intake beds, as they’re known, or the rivers themselves, but that does have to be balanced against extraction, and there are portions of New South Wales and Southeast Queensland where the extraction rates are greater than replenishment.

Glen Paul: Right. So what are the ramifications then of less groundwater recharge?

Dr Smerdon: Well I guess what we’ve seen in the hundred years of data that we really have, is you do see that rather famous decline in the pressures from over the last hundred years or so, you know as a result some of those bores will possibly not flow, some of the springs possibly not flow, but initiatives such as the Great Artesian Basin Sustainability Initiative, so the capping and the piping and sort of cleaning up a lot of those bore drains has actually helped, and you can even see in the data for the last ten years where you’re getting some of that pressure recovery, which is quite important.

Glen Paul: Now you did touch on climate earlier. Has climate change been factored into impacting this water refill?

Dr Smerdon: Most definitely. But I guess compared to a lot of other assessments of water resources, because we’re working with this big, deep, old groundwater resource, the climate scenarios that we’ve looked at are quite short, relative to the geologic timeframes. So, you know, we have looked at the climate aspect, and there are scenarios where you’ve got more or less recharge to the GAB occurring in the future, but that implication is a lot less than the extractions that we think about.

Glen Paul: Now obviously it was a massive project, 2½ years in the making, and a huge expanse of area to cover, who actually funded the assessment?

Dr Smerdon: It was jointly funded, so by the Department of Sustainability, Environment, Water, Population and Communities, so a Commonwealth Department, and the National Water Commission, so it was a 50/50 split.

Glen Paul: And what were the major surprises in the assessment?

Dr Smerdon: I guess the surprises were, in terms of the findings, the complexity, the geological structures really popping out in controlling or governing the groundwater conditions. So it had been long suspected if you have faults and ridges, and that sort of thing, that that would impact the groundwater flow conditions, but you know we’ve got them all mapped out now, and we’ve got lovely maps of where the GAB actually is now shown to be in contact with older basins that are underneath the GAB, so even older, where you have these connections across different basins. That was a bit of a surprise for us.

Glen Paul: And so can water from these then flow into the Great Artesian Basin, or are they kind of separate water containers?

Dr Smerdon: I guess they’re best viewed as separate reservoirs that have different amounts of connection. So picture the GAB as a large groundwater reservoir, you’ve got these other groundwater reservoirs underneath it, and in some cases they’re connected really, really well, so you’d have possibly water being transferred from one of those basins upwards, or from the GAB downwards into those basins. And then there are some locations where the connection’s not very good, and so you don’t have that movement of water back and forth.

One of the outputs from this work is a series of maps that actually illustrate where you’d have the potential for connection versus areas that you don’t.

Glen Paul: Look, it might seem a way off, but just how much life has the Great Artesian Basin got left in it, do you think, to be useful to the Australian farming community?

Dr Smerdon: Well hopefully for quite some time. I mean it’s been a resource that’s been used quite heavily for the last century, but it would have been a resource that was used even before that. But as we look at it we do see pressures decreasing in some parts of the basin, and that’s just purely from natural phenomenon. So in the western part of the GAB it’s just not recharged in today’s climate as it would have been thousands of years ago, so the natural consequence is that you have a decrease in the pressure, and it has nothing to do with our influence on it.

Other parts of the basin, where you’ve got I guess higher densities of activity, both from different extractive industries, so you do have more decrease than you’d have otherwise naturally occurring. So hopefully (chuckles) for quite some time.

Glen Paul: (Chuckles). OK. And where can people actually get their hands on the report?

Dr Smerdon: All the reports are available via the CSIRO website, so if actually people Google Sustainable Yields, or Great Artesian Basin Water Resource Assessment, you’ll come right to the website, and there’s quite a raft of reports, ranging from sort of the technical detail, up to higher level ten or 12 page overviews that are there.

Glen Paul: OK. Well thanks very much, Brian. I imagine there’ll be plenty of interest in this report, so thank you for taking time out to discuss it with me.

Dr Smerdon: Very good. Thanks.

Glen Paul: Dr Brian Smerdon. And to find out more about the research, or to follow us on other social media, just visit www.csiro.au.