SRA Annual Report 2024-25: Resetting the River Aller on Exmoor
A major floodplain reconnection project on the National Trust’s Holnicote Estate near Selworthy has resulted in dramatic changes, part-funded by Somerset Rivers Authority (SRA) and several others.
Inspired by innovative ‘Stage 0’ river restoration techniques pioneered in the US state of Oregon, in 2022-23 the National Trust filled in 1.2km of the River Aller, fixed 700 tonnes of local timber to the floodplain, planted 25,000 native trees and sowed 250kg of floodplain wildflower seeds.
Researchers from several Universities (Exeter, Loughborough, Nottingham, and Sweden’s Umeå) have been monitoring subsequent changes in water flow, water quality and habitat. Initial findings published in October 2024 showed:
- higher ground water levels across the site, in some places by more than 1 metre
- increased lag times between rainfall and stormy surges of water, and an average 38% reduction in downstream flood peaks
- water cloudiness (turbidity) down by 41% following restoration
- lower levels of fine sediments further downstream
- aquatic habitat up by 1780%, from 0.18 hectares to 3.42 hectares
In summary: slowing and storing water is reducing flood risks for places downstream, such as historic Allerford and Bossington. Water is being cleaned, and a superb jumble of habitats created for plants and animals.
This big River Aller reset followed a series of smaller, local National Trust natural flood management works part-funded by the SRA. The National Trust also recently completed a 125-hectare extension of the Aller project upstream at Tivington Farm, part-funded by the SRA.
On 1 April 2025, for all these elements combined together, the National Trust was awarded the UK River Prize 2025 for catchment restoration.