Sharing the story of Burdens Marsh wetland restoration works at the 2025 Sloping (Slopen) Main community field day

On Wednesday the 21st May 2025, NGT staff (Mark and Bec) joined the Tasmanian Land Conservancy (TLC) team at their Sloping Main Reserve on the Tasman Peninsula, to share the story of the recently completed wetland restoration works at Burdens Marsh. As you might recall from our newsletter last month, major remedial works to reverse the impact of past changes to the hydrology of wetlands across the site were recently completed, so this was our chance to take a closer look at those works with the community.

The sun was shining and the autumn temperature during the afternoon was absolutely perfect, as our audience of around 40 guests gathered, ready to enjoy a few hours exploring the marsh.

The natural ocean outlet at the beach

After a brief welcome and introduction by Cath Dickson from the TLC at our initial meeting point, we made a beeline for the location of the currently dry intermittent outlet/inlet that connects the saltmarsh with the ocean. It was here that we began to share the complex story of change since the arrival of Europeans in the early 1800s, and how this began to alter the wetland from how it was known for millennia by the local Pydarerme people (of the Paredarerme nation).

Both the landform itself and the species composition within the saltmarsh tell us that this is a wetland that historically could experience wide fluctuations in hydrological regime, depending on climatic conditions. During wetter phases, the mouth could wash out and open regularly, allowing tidal flows of seawater to then also enter the marsh more regularly.

However, during drier times, and the longer the time that would elapse between flow events, the greater the potential height of the sand bar that would build up across the mouth, which in turn would increase the depth of inundation that would occur when the next fresh inflows occurred. Then, once a sufficient depth of water backed up and inundated the marsh and began to spill over, the mouth would naturally reopen once more.

By scouring the outlet of deposited sand, back down to bedrock, these flow events would allow for subsequent periods of tidal exchange (inflows of seawater into the saltmarsh on high tides) to occur for weeks or months, before the mouth would once again gradually close over with sand drift and the cycle (either long or short, depending on weather patterns at the time) would begin again.

We discussed how deliberate management (openings) of the outlet to the sea over much of the past two centuries have been undertaken with the goal of optimising the grazing value of the saltmarsh. That philosophy of more regular human intervention is now able to be reviewed, given that livestock grazing on the saltmarsh no longer occurs.

The old tidal weir and levee bank near the mouth

From there it was a short walk up the currently dry outlet, to the location where a levee bank and tidal weir – constructed c. 1990 by John Price, the previous owner – were recently remediated. A number of people who attended our 2024 field day commented on just how different this spot now looks! This is the place where John had the ability to prevent tidal ingress into the marsh after mouth openings, as part of his management approach to support his grazing enterprise.

Beyond the obvious aesthetic difference, we discussed the value of now removing this constriction point for flows (in both directions), given its potential influence on the future natural functioning of the mouth, and the ability to convey maximum tidal flows to the saltmarsh after natural openings. This reflects the change in management philosophy from agricultural production to conservation, since the TLC purchased the saltmarsh for addition to the Sloping Main Reserve.

While we were at this spot, we also heard from:

• Cath Dickson, who explained the vegetation and ecological monitoring that the TLC have established to track changes in the biodiversity values over time.
• Bec Sheldon, who explained NGT’s hydrological monitoring, which will sit alongside and help inform any trends observed in the vegetation monitoring within the saltmarsh, given how wetland ecology is driven by hydrological regime.

The main saltmarsh

The rest of the afternoon was spent slowly making our way south through the main saltmarsh, which gave us an opportunity to inspect the various methods for drain backfilling that had been employed – and to give attendees some understanding of the significant scale of the network of channels that have now been remediated.

If you’d like to take a birds eye look around the site, then feel free to navigate your way around the photo below which I took the following day and shows all the remediated drains across the saltmarsh. You can use the zoom feature in the toolbar above the image to take a closer look…

Optional dusk walk to Mungaratya / Turners Lagoon

For a number of the super keen attendees who didn’t have to rush off, we closed out the day with an optional dusk walk to see the restoration trial that NGT now has in place for Mungaratya / Turners Lagoon, a freshwater marsh on the eastern side of the Sloping Main Reserve.

Not only has this wetland been drained for more than 50 years, but unfortunately when this occurred, the artificial outlet drain itself was superimposed on the former natural overflow location, obscuring the precise natural full supply level of the lagoon.

As a result, we’re taking a staged approach to restoration, informed by key information like the memories of locals who remember the wetland before it was modified, aerial photography of the site prior to drainage, and the modern Digital Elevation Model (DEM) which accurately maps the terrain at the site. In turn, we can use the DEM to test and calibrate our understanding of past and future predicted inundation extent. The spillway will now give us the opportunity to trial and (if needed) adjust the water level in real time, when we next get enough rain to fill the wetland again for the first time.

Eventually, once the trial phase has been completed and we are confident to set an ongoing, restored, full supply level for the wetland, these works will be able to be made permanent. To help you with your bearings, here is a view looking north over a dry Mungaratya / Turners Lagoon, and its location relative to the saltmarsh:

Finally, if you missed the field day, but would like to see the notes that were provided to attendees, you can download them here, or take a look in the pdf viewer below.

Now we patiently wait for some decent rainfall to arrive, and the chance to tell the story of how the wetlands across the site are bouncing back to life!

This project is being delivered by NGT in partnership with the Tasmanian Land Conservancy, with support from the Purryburry Trust and a grant from the NRE Tas Threatened Species Partnership Grant Program supported by the Tasmanian Government.