Detailed design and licence application for removal of the Mill of Eden Weir, Scotland

Introduction

The Deveron River is a celebrated salmon, sea trout and brown trout fishery and is one of the top salmon fisheries in Scotland. The Deveron is situated in Northeast Scotland within the counties of Aberdeenshire and Banffshire and has an overall catchment area of 1266 km² (489 miles2) and a length of 96 km (60 miles). The Mill of Eden Weir is situated on a tributary of the lower Deveron named the King Edward.

Project context and opportunity

Road culverts, weirs, bridge aprons or excessive natural large woody debris accumulations can cause barriers to fish migration. Not only can they stop or delay adults in returning to their spawning streams, but they can stop or delay downstream migrating juveniles and smolts and lead to pinch points where they are more vulnerable to predation. Some barriers, although passable under the right conditions, can become temperature barriers when water temperature limits the physical ability of the salmon to navigate the barrier. The barrier in this project is an old stone mill weir that is 1.2m high and 11m wide. The old weir was previously used to supply water to an old corn mill downstream.

Project aims

The Mill of Eden weir is restricting access for Atlantic salmon, trout and eel, and by removing the weir, the project team will open up access to over 11 km of habitat. In this project, the team will take the steps needed to prepare for dam removal, including conducting field surveys, a geomorphic assessment, a topographic assessment, sediment sampling, a hydrological assessment and hydraulic modelling, and a flood risk assessment.

Project achievements

The Mill of Eden weir removal project has reached significant milestones:

• Data collation/review
• Geomorphic assessment: Field data collected, mapped, and summarised, guiding the final design.
• Topographic survey: The Digital Elevation Model (DEM) of existing site conditions is complete and will inform the hydraulic model.
• Sediment sampling/analysis: The Preliminary Risk Assessment (PRA) and sediment sampling reports are complete, guiding on-site sampling studies.
• Presentation of options: AutoCAD drawings and artistic visualisations of proposed design options were completed in mid-June 2023.
• Design development: Detailed design surfaces in .DWG files have been developed.
• Hydrological assessment: Complete, with data feeding into the hydraulic model.
• Hydraulic modelling: Completed with maps showing flood extents under existing and design conditions.
• Flood risk assessment
• Final design outputs: Comprehensive design drawings, method statements, and activity schedules have been prepared, along with the final project report.

These achievements have set the stage for removing the old mill weir, through a programme-supported dam removal grant, which is crucial for restoring the King Edward tributary and improving habitat access for endangered aquatic species.