Before and after transformation — remediating a saltmarsh at Windermere Bay in Tasmania

NGT in partnership with the Derwent Estuary Program, has recently supervised the successful completion of saltmarsh landform remediation works at Windermere Bay. The work was completed on the banks of the Derwent Estuary north of Hobart, in conjunction with Glenorchy City Council’s boardwalk extension and replacement project.

As part of this work, Stage 1 saltmarsh restoration works were undertaken in mid-March 2025, while Stage 2 of the project was completed in late May and early June 2025. To read previous stories for background, please see the initial project article and the stage 1 article. Read on below to see the striking before and after images.

During site remediation works, a large volume of previously dumped fill – which was deposited and spread in the southern inlet of the bay in the 1970s – was removed from both the eastern and western sides of the new boardwalk. The target elevation for the works was determined via baseline data collection in an attempt to re-engage this area of historic saltmarsh with regular tidal inflows, and using this survey was set to levels below 0.9 mAHD. We know from highly accurate GPS survey data of vegetation transitions observed in other parts of the site that saltmarsh communities typically grow in the immediate area below this maximum elevation. However, with the artificial increase in elevation, this area has not experienced natural tidal connectivity for over 50 years. This is because half of the saltmarsh effectively disappeared under the rocky fill that was most likely generated when nearby house blocks were being levelled for development.

The recent works aimed to remove this historic fill material to reinstate the natural landform and encourage saltmarsh extension and improvement in condition through increased hydrological connectivity.

We tied into the edge of existing saltmarsh habitat (now found growing to the east of the works footprint), and extended that target elevation westward to the edge of the excavation area. The gradient was approximately 20 to 30 cm over this distance (e.g. from 0.6-0.7 – 0.9 mAHD). The western (higher) edge of the excavated area was tapered to tie into existing ground levels and allow for inland migration of saltmarsh over time to accommodate future predicted sea level rise. Excavated infill was removed directly to the nearby road verge embankment (which was used as a disposal area) by tip trucks working in tandem with the excavator. Infill material was dumped in the disposal area in consecutive rows adjacent to the road for spreading and compaction.

As with previous projects, we looked carefully for on-ground clues to see if was possible to re-expose the natural surface as the artificial fill was excavated, and there were definitely signs of the original saltmarsh surface and sediments in many places. As shown below, the natural surface level exposed during excavation works reveals darker lagoon sediments beneath lighter areas of infill (often including large cobbles and gravels).

The photos below show the progress in the works zone, between Stage 1 (left) and Stage 2 (right), as the project unfolded over the past few months.

High tides were experienced during Stage 2 excavation works in late May and we are pleased to report that all newly excavated areas were effectively inundated as planned, which confirms that we have achieved the desired level for the works above sea level. Along with the tidal inflows came seed and vegetative propagules which were deposited on exposed sediments and in wrack left behind on existing vegetation, as shown below.

Additionally, and despite it only being a couple of months since the work was completed, some resprouting of Samphire (Sarcocornia quinqueflora) was already evident in the margins of previously excavated areas east of the boardwalk in Stage 1.

Given the early signs of success, we hope and expect it won’t take too long for saltmarsh to begin regenerating and/or establishing in the newly exposed sediments over the coming years – in a zone where the hydrological regime and underlying soil salinity should drive spontaneous ecological recovery.

To track these changes, as well as vegetation monitoring, we have also established a series of ground based and aerial photo-points that will allow us to share the story with you over the years ahead. Some examples of these are shown below…

It will now be exciting for us – and the community – to watch the saltmarsh recovery process unfold in this urban public recreational foreshore area, which – unlike most of NGT’s wetland restoration work – has extremely high public visibility and access. With more high tides due in late June, we will be keeping an eye on inundation levels and awaiting the deposition of more sediment and vegetative material that should help to kickstart the saltmarsh regeneration process.

Saltmarsh restoration and improvement of saltmarsh extent and condition along the foreshores of the Derwent Estuary is vital, given that so much of this habitat has been lost all around Tasmania (and mainland Australia) to urban activities and development over the past century. We are grateful to have had the chance to play a small part in helping to reverse these past detrimental changes at this important remnant saltmarsh areas on the foreshores of the Derwent Estuary.

This project is being delivered by NGT in partnership with the Derwent Estuary Program,
with funding provided by the Australian Government’s Urban Rivers and Catchments Program