The Dartmoor Green Recovery project recently welcomed volunteers from the Environment Agency and a team from Dartmoor Horse Loggers to a site near Princetown. Dartmoor Biodiversity Officer Morwenna explains the use of heavy horses for moorland river works:

In June, we started river enhancements works with the River Meavy. The work took place at the head of the river, just South of Princetown. This section of river is a mix of beautiful, boggy habitat with pondweeds, spearworts and water crowfoot growing in the rivers, and bog cottongrass, sphagnum mosses and heath spotted orchids flagging the banks.

Other parts of the river are less diverse and, where the river is flowing too fast, it is incising into the substrate causing increased erosion and increased dissolved organic carbon, caused by high sediment load in the water. The bankside habitats in these areas are also less diverse, with drier vegetation and fewer plant species growing.

A river habitat survey which looked at this part of the Meavy found the in-river and lateral habitats were of poor quality, due to poor diversity in flow types, and river features like side bars and riffles, caused by sediment deposition. Low scores in complexity and continuity resulted in a poor score for the lateral habitats. A slower flow, and more complex flow regime would help to improve the lateral boggy habitats, whilst reducing overall erosion and therefore dissolved organic carbon in the water. 

To improve this river habitat, we have worked with team members from the Environment Agency, with specialists in geomorphology, biodiversity and fisheries advising on the best actions to take. The use of whole trees to pack into the river was decided as a great option, because the brash and trunks from trees would raise the water level and help to trap sediment, raising the river bed, whilst allowing fish passage through branches.

In March, we gathered the trees by creating glades and rides in a broadleaf woodland near the reservoir and thinning it to improve light and biodiversity in the woodland. The trees were stored at the top of the Meavy and observed for any bird nesting activity in the months in-between. River work like this can only happen between June and September, due to the fish-breeding season, as fish usually have eggs spawning in the time outside this season. 

The work began on 17 June, when we were joined by Will from Dartmoor Horse Loggers, and his two horses, Polly and Beano. Will and the horses did an excellent job of pulling logs and brash from the pile, and dragging them downstream. Using horses for this work was preferable to using diggers or quad bikes, because the uneven and boggy ground leave few options for a vehicle to access, so with a few trips, the ground disturbance could have become significant. Horses however, were able to find a number of routes between boggy ground and tin-mining spoil heaps, reducing the amount of erosion significantly. 

As the trees were pulled down river, a wonderful team of volunteers started to pack them into the river. Teams from different groups, including Environment Agency, Arcadis, Babcock, and our regular South West Lakes Trust group helped with this over five days. We are really grateful to all the volunteers for their time, energy and enthusiasm on this project. 

Volunteers were breaking the trees into smaller pieces so they sat more tightly in the river, and packing brash into gaps so that the river would be fuller and sediment would collect among the brash. Larger logs were placed on corners that would allow water to be pushed over the bank more regularly, and across the river laterally in some wider parts, to allow the water to flow over the banks during peak flows. 

Over time we will be able to observe the changes that are made by increased flooding and sedimentation, and hopefully we will create more patches of boggy habitat with space for more invertebrates, birds and a greater diversity of plants.

This work was funded by the Environment Agency’s Water Environment Improvement Fund and is part of the wider South West Water funded Dartmoor Green Recovery project.