Restoration is reviving Rowan Swamp – new water-level data unpacked
Rowan Swamp is a 150 hectare wetland feature, situated near the township of Lake Rowan, in the Goulburn Broken CMA region, about 40km north of Benalla.
Three years ago NGT began an eco-hydrological assessment of the Rowan Swamp Wildlife Reserve in partnership with Parks Victoria. After an investigation of the history of the wetland and documenting the changes to its eco-hydrology, a trial sandbag structure/weir was constructed with the help of the Yorta Yorta Nation Aboriginal Corporation crew. The trial structure aims to reverse the detrimental impacts of erosion at the wetland outlet, enabling the wetland to hold more water again. Since then we have been monitoring water levels to see what impact our trial is having. Lachie explains the latest results:
In a previous article, I unpacked our first analysis of water regime change at Rowan Swamp since the installation of a trial restoration structure in 2022. And now, 18 months later, we have had two more fill-and-dry events. The water level data confirms our original observation that mitigation of artificial losses (as a result of erosion of the natural outlet) is keeping this wetland hydrated for longer into the summer months. The chart below shows water levels at three locations across the wetland including in the wetland proper (RS_01 – grey line), in the weir pool created by the structure (RS_02 – orange line), and in the open channel downstream of the structure (RS_03 – blue line). It is the water depth in the wetland (RS_01 – grey line) that is of most interest in terms of the extent and duration of inundation of the wider wetland area. Notice that the grey line below drops off more slowly post-restoration, maintaining a higher water level further into summer.
Based on the first observed dry-down period post-restoration, we estimated that the inundation duration for the wetland was extended by three weeks. One of the subsequent dry downs (in November 2023) is consistent with this, but another event in early 2024 was much quicker (10 days longer than pre-restoration). This is illustrated in the chart below which also shows a comparison of rainfall across the same periods. Notice the orange line below (pre-restoration) reaches the minimum water depth sooner than in the other three post-restoration dry downs (blue, grey and yellow lines). Based on what we have seen with this additional data, we can be confident that the wetland will now stay wetter through spring and any late-season rainfall, similar to what we saw at the start of this year, will have a foundation to add to, rather than just generating a flashy inundation event. Of course, we are yet to see any significant stream-flows this winter and the wider wetland remains dry. We can’t expect it to fill up every year but we know that, when inflows do occur, this wetland now has the ability to make the most of inundation events and spark a “coming to life” such as we have witnessed over the past couple of years since restoration.
Another observation gained through our water level monitoring is the inundation of the pool immediately upstream of the restoration structure. Since installation, this pool has remained permanently inundated (see RS_02 orange line in the top chart), even during the significant dry period experienced during autumn this year. I noticed when I was out there last week that some clumps of tall spikerush (Eleocharis sphacelata) are really starting to take off in this section. We also saw a juvenile white-bellied sea eagle when we first arrived last week. Unfortunately, I didn’t get a photo but its presence is evidence that this wetland is heading back in the right direction, in terms of ecological function.
The initial planning and structure installation works were supported by Nature Glenelg Trust, through funding from the Australian Government’s Murray–Darling Healthy Rivers Program and Parks Victoria.
