High flows present restoration challenges on the Fleurieu Peninsula, SA

Last month we shared with readers the story of recent works at Stipiturus Conservation Park, near Mt Compass, south of Adelaide. Sandbag structures first installed in 2017 were covered with soil, using a small excavator, in early April this year, converting them from temporary to permanent. The structures were installed to block flows within an artificial drain, lift water back to the natural surface and direct it through the original, meandering creekline that brings seasonal surface inflows to Glenshera Swamp. In doing so, the structures restore habitat and provide enhanced opportunities for the natural improvement of water quality prior to inflows reaching the main part of this important Fleurieu Peninsula Swamp (a critically endangered ecological community at the national level).

Ideally, earthworks like this are given several months to settle and become vegetated prior to being subjected to high flows. Any bare earth is always quickly colonised by plants. Both the above and below-ground parts of plants help hold soil in position and prevent erosion, when soil is subjected to flooding and high velocity flows. At NGT we love rain but sometimes would prefer it to fall with less intensity so recently after restoration earthworks! Through the day and evening of Thursday 22nd June the Fleurieu Peninsula received a drenching. Bureau of Meteorology rainfall data provides some indication – in the 24 hours to 9.00 am on Friday 23rd June rainfall was 36.6 mm at Kuitpo and 43 mm at Parawa. These two locations are the closest official BoM sites to Glenshera Swamp. Rainfall in the catchment of Glenshera itself was likely just as high, if not higher. On top of an already soaked catchment, this event led to some pretty high flows into Glenshera. We don’t relish the sight of our restoration works being damaged, but the videos captured by our time lapse cameras are something we thought readers would find interesting!

Camera Stipi 01 is trained upon Structure 1, the most upstream of the recently covered structures. At the beginning of the video you can see that despite the earthworks having been completed only about 5 weeks prior, there is already some vegetation established on the structure. At 2 seconds (22nd June) the structure becomes completely submerged. Flows presumably persisted and increased during the night (when the cameras do not operate) when it appears the damage to the structure occurred. When the flows subside over the following days, the damage can be seen. There are similar patterns of flow and damage observable at camera Stipi 02 (Structure 2), Stipi 04 (Structure 3) and Stipi 05 (Structure 5). Downstream of Structure 5, despite recent earthworks, no damage was evident, which is a good result as it shows that the ‘re-meandering’ of the creek has been successful; all flows, including very high flows, are now directed into Glenshera Swamp and do not re-enter the artificial drain further downstream (where it still partially exists).

We have undertaken some repairs to the damaged structures – you can see them appear at 8 seconds on cameras Stipi 01, Stipi 02 and Stipi 04 – to keep them functioning under low to moderate flows and to prevent further damage. However, we’ll need to come back during the dry season to repair them thoroughly. Such are the occasional hiccups on the wetland restoration journey. At the end of the day, too much water is not a bad problem to have when you’re restoring wetlands!

This project is being delivered by NGT in partnership with Friends of Stipiturus and Hesperilla Conservation Parks, funded by the National Parks and Wildlife Service, Friends of Parks Partnership Grants Program.

Ben Taylor