At Insh Marshes in the Cairngorms, Scotland, uprooted tree trunks have been installed in the river, helping to return a straightened channel to a natural meandering course – improving habitats for nature and boosting climate resilience.
Stretching between Kingussie and Kincraig along the River Spey, RSPB Insh Marshes is a 1,000-hectare floodplain. In the 18th and 19th century, humans experimented with modifying the floodplain for agriculture – straightening several of the rivers which feed into the floodplain and building walls (or ‘embankments’) to keep rivers like the Tromie straight and narrow.
These modifications are now causing more harm than good, as they fail and fall into disrepair, requiring expensive and damaging interventions. The Insh Marshes team need to look to alternative solutions to make the reserve more resilient to the impacts of climate change, which include increased seasonality and intense rainfall.
Following extensive community consultation, the first of the floodplain restoration projects began in early 2022. The project aimed to slow the flow of water and provide better habitat for fish to spawn, rest and feed through the installation of uprooted trees in the river Tromie. Environmental consultants, EnviroCentre, undertook a study to investigate options for this project, and the final project was a result of careful hydrological and morphological studies and consultation with statutory agencies.
Woody islands in the stream
In autumn 2022, this project was successfully carried out by local contractors, McGowans. Technically known as “Large Woody Material”, nine spruce tree trunks were strategically placed in the river Tromie. Kindly donated from the nearby Wildland Limited estate, these trees needed to be carefully uprooted, with the root plate structure intact, and transported around two miles to the river Tromie. Here, they were buried in the riverbed with the root plate facing upstream, replicating natural events but securing the trunk and root plate further into the riverbed and shingle banks.
Retaining the root plate is a tricky part of the process, but crucial. Once lodged in the river, the root plate alters the flow of the river. During flood events, rock, sand and silt get deposited by the river, building up in different ways round the root plate, creating new habitats like shingle banks. These new habitats should benefit a range of species including rare insects, like the 5-spot ladybird and northern silver-stiletto fly.
Benefits for nature
The range of habitats created by the simple and effective installation of woody material will provide spawning, feeding and resting habitats for fish such as Atlantic salmon. A wide range of aquatic invertebrates will also benefit from this ‘messier’ habitat, and birds like dippers, kingfishers and goldeneye will reap the benefits of healthier invertebrate and fish populations.
As the river changes, re-wriggling its way across the floodplain, the team are keeping an eye on the changing landscape, using water depth monitoring, drone surveys, time lapse cameras and fixed-point photography, as part of the Cairngorms Connect Science and Monitoring Programme. Zooming in, the Spey Fishery Board will be monitoring how the fish population responds to the changing habitat, whilst the Rare Invertebrates in the Cairngorms project will be doing the same for invertebrates.
Over the coming months, the site team are looking to further develop other floodplain restoration projects and are currently in the process of tendering a consultancy to support this work, in line with input from the local community gathered during consultations in November 2020.
This article was originally published on the Cairngorms Connect website. To find out more about Cairngorms Connect, please visit the project page.
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