Preparing for removal of Dollar Weir, Clackmannanshire, Scotland

Conducting the necessary surveys that will potentially lead to removing the ecologically and environmentally degrading Dollar Weir. 

Introduction

The Devon catchment covers 181 km2 on the north shores of the iconic Forth. It starts at an altitude of 458m in the Ochils, taking a winding route through the district of Clackmannanshire.  The upper Devon is not free-flowing, as several reservoirs constrain it. Castlehill is the final reservoir in the chain that provides a source of drinking water for the Scottish people.

Below these reservoirs, the river tumbles over the waterfall at the Cauldron Linn. This is the upper limit for most natural fish migration, except the wily climbing eel elvers. Below here, the river becomes home to many fishes such as Atlantic salmon, sea/brown trout, European eel, lamprey species and the stone loach.

The species that can reach up the river this far live amongst the ash, sessile oak and alder woodlands that flank the river. Downstream the river becomes agricultural within the flatter land, taking a more meander-based morphology. Here lies the Dollar weir – a large stone-based weir that impounds the water for ~200m, reaching 2.16m in height and spanning the river by 43m. It was built pre-1943 for water power and abstraction for agricultural and bleaching mills.

The Devon continues through agricultural grasslands, meeting several key and important spawning streams that flow directly from the Ochils. The river has gravel and pools around the town of Alva, with long glides and deep pools providing rest amongst the spiked water milfoil, pondweed, and duckweed, where fish rise to the surface to snatch flies.

The Devon flows into the Forth at Cambus, but not before meeting its final impoundment adjacent to the Diegeo bond. However, this remaining dam will be removed in the coming years.

At a glance

Project typeDam removal (pre-demolition)
Project statusComplete
CountryScotland
RiverDevon
Potential km to be opened20.39
Key speciesAtlantic salmon, sea and brown trout, lamprey, European eel, stoneloach
Project websiteForth Rivers Trust

Project context and opportunity

The River Devon has the potential to increase significantly within its current classification of ecological potential. Those who know the river recognise its special place in the Scottish effort to preserve the iconic and special freshwater fish, mammal and bird species. However, nationally it has not received much attention as other rivers with excellent potential for fish spawning; this is partially because of a significant chemical fish kill in the mid-reaches in 2012, which reduced aquatic life.

The Dollar weir is privately owned, sitting within a large gravel bar and a good-sized mature, semi-natural woodland margin. The 2.16m high weir starves the downstream river extent of these gravels, except when over-topped with force in winter and summer spates.

Removing the weir is an exciting but challenging opportunity for Forth Rivers Trust and the local users of the river environment. The aim is to undertake the required surveys and studies of the weir, the wildlife, and the general impact of the potential removal of the weir on the adjoining area. The project team hopes to utilise all this new data and information about the weir to plan its removal in discussion with the owner, the local authority, and other key stakeholders.

All being well, the work will progress to the next stage of fully designing the removal and restoration/naturalisation of the river in 2024. With the promise of Diegeo removing their weir in future, locals can enjoy an entirely free-flowing lower Devon that can be a happy home for wildlife.

Project aims

FRT will take a standard approach to explore removing barriers and dams within the Forth catchment using a Prince-2 derived staged project management approach. This approach will instruct, gather, report, detail and examine critical information that will potentially lead to removing this ecologically and environmentally degrading structure.

The first stage is to start the project, including securing funds, ensuring the project is feasible, gaining a good working relationship with the weir owner and undertaking a risk assessment.

The second stage is gathering surveys, drawings, and field studies to inform about the key impacts of removing the weir. This includes an ecological study to ensure that if the removal process goes ahead, it is safe and any impact can be mitigated against protected and important species/habitats. This also includes studies of the river’s morphology, flow regimes, and flood risk for the site.

The third stage is project design. This entails gathering all information with relevant stakeholders, the potential contractor for removal, and several other people with key specialities, such as engineers and hydrogeomorphologists. Having identified the constraints and opportunities for removing the structure, the project team can design how this will happen and what this will look like.

The final stage for this project is the preparation, submission and liaising with SEPA about the licence for removing the weir. For this, the project team must submit all the gathered information and show their complete understanding of how the weir can and should be removed. They must also complete another set of licenses, such as those to disturb protected species (e.g. otters) and waste licences. Lastly, liaise with the local authority about whether this requires planning permission.

Project achievements

This project was complex in nature, especially given the size of the structure, the proximity of dwellings in the adjacent holiday park, and the presence of invasive and protected species. In splitting the components into four separate phases and commissioning a range of additional surveys internally and externally, including but not limited to flood risk modelling, core sampling and geomorphological surveys, the project was completed and confirmed that this weir can be safely removed.

The project was completed in October 2023.

Partners

Forth Rivers Trust