Our Water Environment: restoration in the River Avon catchment, Cairngorms National Park

Guest blog - Jos Milner, Tomintoul & Glenlivet Landscape Partnership

The River Avon is a tributary of the River Spey in the north of the Cairngorms National Park, important for spawning salmon and other wildlife. Over recent years, Tomintoul and Glenlivet Landscape Partnership (TGLP) has been working with the Spey Fishery Board (SFB) and Spey Catchment Initiative to deliver projects to improve ‘Our Water Environment’.

The overall aims were to restore and enhance parts of the River Avon catchment within River Spey Special Area of Conservation (SAC). The intention was to make the river and its wildlife (designated features being Atlantic salmon, sea lamprey, otter and freshwater pearl mussel populations) more resilient to the pressures of climate change, while reducing agricultural pollution and habitat loss through improved water margins and in-channel habitats. In doing so, it is hoped the projects will contribute to natural flood management and improvements for biodiversity and water quality, as well as protecting key infrastructure, farmland and associated livelihoods.

National Lottery Heritage Fund (NLHF) funding enabled TGLP to bring in agricultural consultants to prepare agri-environment and climate scheme (AECS) applications to Scottish Rural Development Programme (SRDP). These have supported over £240,000-worth of capital works across 7 farms, including green engineering projects, riparian fencing, alternative livestock watering schemes and bankside tree planting.

Green engineering projects on two farms are the focus of this article. They demonstrate river restoration techniques delivered through the ‘Restore (protect) river banks’ AECS option which focused on using natural materials in flood-prone areas. Using green engineering for bank protection has the advantage over more traditional engineering techniques of absorbing and diffusing energy from the moving water rather than reflecting it which causes problems elsewhere. The complex surfaces of natural bank protection also contribute to trapping sediment, slowing down the flow of water and providing niches for a variety of aquatic species.

Log jam on Conglass Water, a tributary to River Avon, a) during construction in Sept. 2017 and b) three years later in Aug. 2020.

The first project involved a small-scale engineered log jam (Fig. 1) and two willow spiling interventions on Conglass Water, a tributary to the Avon. Instability of the river channel was affecting adjacent land use and field boundaries, while fields and one property have been identified by Scottish Environment Protection Agency (SEPA) as being at risk of flooding during 1:10 year flood-events. The farmer was keen to find a green solution that would also improve the quality of the water environment. This short film describes the project.

Both the log jam and willow spiling were designed to protect the banks from further erosion and sedimentation of the water course while absorbing energy during high flow events and providing new habitats. Using locally‐sourced natural materials to mimic natural channel features and encourage the restoration of natural river processes added to the sustainability of the solution.  

The log jam was constructed using trees from a plantation just 500m from the site, so minimising transportation costs and logistical problems. It consisted of two stacked layers of logs aligned along 110m of the bank (Fig. 2). The base layer comprised the lower trunks (diameter approx. 0.5m) and root balls, with the remainder of each tree forming the upper layer to the height of the existing bank. The river bed was lowered locally to allow the root ball to be secured into it and the trunk to lie close to the bed. The root ball of one tree overlapped the tip of the next tree upstream. Arrowhead ground anchors were used to secure the trees to the bed and banks. Posts were also driven in at 2-3 m intervals along the length of the log jam and steel wires secured the logs to the posts and bank. Finally the branches of the trees were trimmed back.