Back Burn and Coul Den Reservoir works

The Back Burn at the Coul Den Reservoir has been heavily altered over more than 100 years. The original burn course was diverted in 1890 when the reservoir was first built, with most of the flow being channelled under a sluice gate and through a bywash channel around the edge of the reservoir and hillside. The restoration work forms part of the wider River Leven project and involves restoring more than 5.8 km of the Back Burn to a more natural flow. It was commissioned by Fife Council and the Scottish Environment Protection Agency (SEPA) and is managed by Fife Coast and Countryside Trust (FCCT), supported initially with funding from SEPA’s Water Environment Fund (WEF).

The Coul Den site was tightly constrained with limited access for machinery due to narrow pathways and dense tree cover. Both the condition of infrastructure related to the previous reservoir construction and the ground conditions were unknown in places, leading to certain assumptions during the design and construction process. Owing to net zero objectives, where possible, material had to be reused or redistributed on site. However, there was limited space within which to do this, particularly because of the way the site is managed, including the wild flower meadows. As well as being important for nature, the design was required to improve accessibility to the site, which is much loved by local communities.

The unknown soil and sub-surface conditions meant that elements of the design had to be field-fitted on-site, with the alignment and gradient of the new channel adjusted to better suit local conditions while still meeting its ecological goals. Sections of the footpath, which in places form a circular route around the nature reserve, were elevated and set back with a new bridge and boardwalk installed. This has allowed the burn to flow naturally under these structures while allowing walkers to enjoy the new viewpoints and wetland areas created. Sustainability was considered throughout the design, which made use of locally sourced materials (including stone from a local quarry) and redistribution of all excavated material on-site, reducing travel and carbon emissions. For example, gabions stripped from the old outflow channel were removed and the gabion rock was redistributed along a section of adjacent hillslope to keep transport emissions as low as possible. This was buried under topsoil or turfs to ensure quick re-establishment of hillslope vegetation for stability and aesthetic purposes.

The rerouting of 700 m of the burn back to its original course through woodland and connecting it with what remains of the reservoir offers huge benefits to wildlife within the local nature reserve. The two nature-like rock ramps will support resident fish (such as brown trout) movement upstream and downstream through a longer section of the burn and over two weirs. The extended wetland and wet woodland areas provide vital additional habitat for amphibians, invertebrates and other wildlife and will improve carbon storage at the site. The community benefits from improved access locally at the reservoir and to wider footpath networks within the nature reserve, as well as a more natural environment that offers better resilience to future climate change and benefits to health and wellbeing.

A further phase of works is due to be constructed in 2026, downstream within Balbirnie Estate.

Thanks to the Fife Coast and Countryside Trust for the images.