Allt Lorgy site visit, Scottish Highlands

8 members attended a fantastic site visit to the Allt Lorgy in Cairngorm on Wednesday 13th April 2022, the first since the beginning of the pandemic! This project won the UK River Prize in 2020 for reach scale, process-based river restoration resulting in a self-sustaining system, and now provides an important demonstration site for landowners, Fisheries Boards and students.

The river had been canalised, straightened and regularly dredged in an unsuccessful attempt to intensify floodplain land use, creating 2m high embankments and a uniform, armoured bed. Large blocks of stone had been used in an attempt to reduce the subsequent erosion and incision - these were replaced with large woody material. The Seafield Estate gave the designers a blank canvas, providing the work improved the fishery of the Spey. Prior to the works, no sea trout or salmon were observed in this stretch; both species now breed here.

The main aim was to remove constraints and kick start natural sediment transfer processes and dynamic morphology. As one of the first projects in Scotland using large wood to restore natural processes, every structure was initially deemed to need a (CAR) licence. SEPA subsequently acknowledged large wood as an environmental service, thus obviating the need. None of the large woody material was anchored, and only one structure has moved despite many spates because the whole tree root ball is used, sunk into the bed or banks of the river.

Old aerial photos showed that the river was much more dynamic and moved over the whole floodplain. Large wood in the form of whole trees, including the root ball, was introduced at key locations with the root ball facing upstream. The machine driver ditched around the root plates of riparian trees before pushing the trees over and burying the root ball in the bank. Embankments were removed to release the river, and the material generated was used to block drainage ditches at the top of the stretch to encourage development of wet woodland. Although trees were planted & protected using vole guards, natural regeneration did far better (especially on disturbed ground) so no planting will be undertaken in future schemes, saving yet more money.

Showing the prolific natural regeneration of Scots pine, willow and birch

The total cost was just £50k: £17k consultancy (fluvial audit and restoration plan), an expensive deer fence to protect newly planted trees, and just £7k for the physical works -removing embankments and adding large wood. Local primary school children helped plant trees and undertake some of the monitoring, thus engaging the community and hopefully spreading the message about the value of large wood amongst the fishing community.

Monitoring includes repeat topographical survey (to show physical evolution of the channel), sediment sampling, habitat suitability indices for spawning salmon and redd/juvenile counts as validation. Drone footage is not possible due to CAA restrictions. An ecological survey carried out prior to the works could be repeated, but funding for monitoring is always difficult to obtain. Two important points: FC guidelines still talk about the need to remove fallen timber from rivers. And people felt there was a need for a method for recording carbon storage benefits of river restoration.

Showing increased channel width, gravel bars and diversity achieved by using large wood

Thanks are due to Duncan, Penny and Hamish for leading the site, explaining the project and answering the many questions. RRC is planning to arrange further site visits for members as they are so valuable for knowledge exchange and learning.