A ‘patchy’ season for wetlands in the cross-border zone, but the upgraded outlet structure in the Mt Burr Swamp Stage 2 restoration area is working nicely

It is proving to be a very ‘patchy’ season for wetlands in the cross-border zone between South Australia and Victoria.

For instance, uneven rainfall distribution in the southern Grampians region means that while Gooseneck and Brady Swamp have received inflows from the Wannon River, NGT’s neighbouring reserve at Walker Swamp, which primarily receives water from the plains to the east of the Grampians, is still quite empty (and hasn’t changed a lot since June) as shown in these images from July:

Nearby at NGT’s Green Swamp Restoration Reserve, a minor catchment inflow has put a shallow sheet of water across the deepest part of the basin, but the swamp is still well below full. [By the way, to remind you of what it looked like when it last filled 3 years ago, please read this article.]

For these and many other wetlands like them, now that the days are lengthening and spring warmth is upon us, we’ll need a significant dump of rain soon, or it may be a matter of waiting again for next year…

Interestingly, a little further west, many of the cross-border streams (like Morambro, Naracoorte and Mosquito Creeks) that flow from western Victoria into South Australia have been flowing, which is a nice change after many years of limited (or even no) flows over the past few decades.

Hence, Lake Ormerod (fed by Naracoorte Creek) is looking great, and Hacks Lagoon (fed by Mosquito Creek) is now overflowing into Bool Lagoon.

For anyone who wants to experience some bustling wetland birdlife (away from the coastal areas currently being impacted by bird flu), the Hacks Lagoon portion of this Ramsar Wetland of International Importance is a cacophony of noise at the moment!

However, even though many local districts have had enough rainfall to leave some water in paddocks and for a few wetlands to reappear, if you travel around more broadly, the wider landscape continues to appear quite dry compared to how it should be, despite me hearing many people say we’ve had “good average winter rainfall”. To me, it doesn’t feel like it!

For instance, many of the major arterial drains across the South East of SA, especially in inland areas, continue to be dry or have limited flows, and give us insights into a wider story that is unfolding. In many cases, these are drains that not only once flowed with surface runoff, but would often have shallow groundwater discharging into them, which had infiltrated elsewhere into the underlying limestone substrate / aquifer.

In my view, and being acutely aware of declining groundwater trends across the region (especially the areas underlain by a limestone aquifer), this appears to be the big difference in how the landscape is behaving after a seemingly “average” winter today, in comparison to 30 years ago. That is, where the underlying water table has fallen away dramatically from the land surface (leaving the upper soil profile and / or limestone substrate dry), then the ability for the ground to saturate, and to generate flows or sustain inundation of groundwater dependent wetlands into the summer months is greatly diminished. The result is a landscape that takes an ever-increasing amount of rainfall to make up for this deficit, which means that average winter rainfall is simply no longer enough to replenish (or top up) the groundwater and sustain our waterways and wetlands like it once did.

Of course, with every general trend, there are always exceptions and (as we discussed last year, when we addressed a similar theme) we’re very lucky that NGT’s restoration project site at Mt Burr Swamp is one such location.

Underlain by a perched aquifer that has proven itself to be more resilient than the trend impacting the wider regional aquifer, we continue to witness the evidence for how the presence of this shallow water table interacts with the landscape in and around Mt Burr Swamp each winter. For instance, this year, the Stage 2 restoration area has responded very quickly and favourably to local rainfall, despite not being an especially wet winter, with the wetlands fully inundating and now generating sufficient outflows to give our newly upgraded outlet structure a workout!

The contrast to many other parts of the region could not be more stark, now that we are seeing this area full and overflowing again. Indeed, this is what an average winter once looked like across the whole of the South East…

By restoring these wetlands and retaining more water once again in this landscape, as we did last year, we’re topping up the local perched aquifer, and ensuring that this retained store of moisture below the ground – despite being largely invisible at the surface by the autumn – will give us a crucial head-start again next year.

This positive cycle of groundwater recharge and recovery, against the backdrop of a warming and drying climate, is something that we’d like to see incentivised and strategically replicated in more parts of the landscape, to underpin the future sustainability of our wetlands, wildlife and the groundwater system in general, which every regional community in the region relies upon.

The project at Mt Burr Swamp is being delivered by Nature Glenelg Trust, via the Shorebird and Wetland Habitat program,
which is funded by the Australian Government and administered by the South Australian Government.