Morton Quarry Weir, Linhouse Water, West Lothian, Scotland

Removal of Morton Quarry Weir by hand

The River Almond catchment area
The River Almond springs in the eastern flank of Cant Hills near Shotts in North Lanarkshire, Scotland, UK, runs through West Lothian, and flows into the sea at Cramond, Edinburgh (Figures 1-2). It is a 48 km river with a catchment size of 375 km². Most of the catchment area is in West Lothian, which historically supported significant coal and oil shale industries. Historical and modern industry and industrial development have taken a toll on the catchment’s water quality, habitats and biodiversity.

Figure 1. River Almond catchment area © Forth Rivers Trust

Linhouse Water is a tributary of River Almond and one of the 21 baseline surface water bodies (i.e. it drains a catchment greater than 10 km²) in its catchment (Figure 2). It is currently characterized as having poor ecological status due to several pressures, including water abstraction, flow regulation, fragmentation, agriculture diffuse pollution, and point source sewage pollution. Despite the detrimental effects of anthropogenic pressures, Linhouse Water remains a popular recreation area.

Figure 2. River Almond catchment area, and location of Linhouse Water and Morton Quarry Weir © Forth Rivers Trust

The Morton Quarry Weir
The Morton Quarry Weir was a 2-m-high and 20-h-wide structure (Figure 3) fragmenting Linhouse Water, impacting its ecology and preventing fish migration upstream for over 200 years. The year of its construction is unknow, but the weir was a historic relic of the 1800s oil shade industry as it was constructed as part of Oakbank oil works which closed in 1932. The weir location itself (Figure 2) was a spot where poaching occurred, as fish would be stuck in the pool below the impassable structure – evidence of landing nets was found onsite when removal works began.

Figure 3. Morton Quarry Weir © Forth Rivers Trust

Dam removal
Removal of any barrier above 1 m in height in Scotland requires a Controlled Activities Regulations (CAR) licence provided by Scottish Environment Protection Agency (SEPA) who regulate barrier removal projects countrywide. Responsibility of barrier removal is unclear in Scottish legislation. As a result, many redundant barriers remain in Scottish waters, preventing upstream access to local and migratory fish species and impacting river ecology. Land ownership is also more complex than in other European countries, as riverbanks can have private owners and there can be two different owners on each side of the river. Progress remains slow across Scotland for removing barriers, despite barrier removal having been identified as an important issue.

The Forth Rivers Trust is a conservation charity protecting rivers in the Forth and tries to change the tide by continuously seeking out opportunities to remove river barriers, restoring free-flowing rivers for the benefit of rivers, wildlife, and people, and the removal of Morton Quarry Weir was their latest such project. The removal was undertaken as part of the ‘Lost Wee Weirs of the Forth’ project by Forth Rivers Trust which sought to identify small, unnamed barriers in the catchment presenting an issue for fish migration. This project experienced significant delay and poor results due to the refusal of one landowner to remove a barrier and another being determined as geomorphologically too risky by SEPA, and thus economically unviable for removal given its urban nature; both barriers are located in the municipality of Clackmannanshire.

Following this, the ‘Lost Wee Weirs of the Forth’ project then focused on the removal of Morton Quarry Weir (Video 1). The progress began in January 2022 when funding was granted to Forth Rivers Trust to investigate the viability of removing multiple unnamed barriers in the Forth catchment. A heritage drop-in day was held in April 2023 where anecdotal and personal memory-based knowledge was shared, where the Trust’s staff learned of the barrier’s history and connection to the shale oil industry. Removal works of the weir were initially delayed because the investigatory work attempting to track down the weir’s owner was unsuccessful. The demolition works eventually began in September 2023, once the necessary licenses had been obtained and West Lothian Council, owners of one side of the river, had been notified.

Video 1. Removal of Morton Quarry Weir © Forth Rivers Trust

Removal took 10 working days. During this time, works were paused twice due to high water events, but these helped the river’s natural processes along as part of the removal. The weir was located in a steep gorge prohibiting access to heavy machinery and the costs associated with creating such access were exorbitant. Thus, the weir was dismantled by hand (Figures 4-5); a remarkable achievement thanks to the dedication and craftsmanship of the Forth Rivers Trust staff. The removal process involved stripping away the weir’s top concrete layer (Figure 4) as well as the natural cobblestone weir beneath (Figure 5). The cobblestones were redistributed downstream of the removal site to enhance the aquatic habitat in the Linhouse Water. This was a novel, low-cost method that caused minimal disruption to the habitat, and could potentially be replicated in similar projects.

Figure 4. Stripping away the Morton Quarry Weir’s top concrete layer as part of its removal works © Forth Rivers Trust

Figure 5. Removal of the natural cobblestone beneath the top concrete layer of the Morton Quarry Weir © Forth Rivers Trust

The weir removal (Figure 6) has restored access to 8.5 km of pristine fish spawning habitat upstream. Indeed, trout and salmon were spotted at the site attempting to migrate upstream during the removal works. Poaching incidents that used to occur downstream of the weir due to the blocked fish passage have now been eliminated. Surprisingly, during the removal, a 300-360 million years old fossil was revealed belonging to the genus Lepidodendron (Figure 7), an extinct genus of tree-sized lycopsid plants that lived during the Carboniferous Period.

Figure 6. The removal site at Linhouse Water after the demolition of the Morton Quarry Weir © Forth Rivers Trust

Figure 7. A 300-360 million years old fossil belonging to the genus Lepidodendron revealed during the removal of the Morton Quarry Weir © Forth Rivers Trust

The barrier removal cost £25,000 in total and was funded by the European Open Rivers Programme. Sharing the news on social media received an overwhelmingly positive response, demonstrating that there is a growing appetite for barrier removal as part of river restoration. Sharing news of a barrier removal is a good success story and a very visual demonstration of the recovery potential of river habitats.

Challenges
One of the greatest challenges needed to be overcome during this project was the remote location of the site – both site location and valley topography necessitated removal by hand, and with weir’s state of disrepair presented a challenge for staff who had to be very careful as works progressed. Removing the concrete skin atop the weir required caution and care, as there was a 2-m overhang to the riverbed below.

Another challenge presented was evidence of otter (Lutra lutra) near the site during pre-commencement survey works. While their presence was not noted when works commenced, a protected species licence was applied for in advance, and the presence of an Ecological Clerk of Works onsite ensured protection measures were followed and no disturbance was caused to this protected species.

Funding limitations posed an additional challenge that needed to be overcome. Overheads increased by ~30% over the course of 2022 and the intricacies of CAR licence applications for impoundment modification/removal meant budget spend was slightly greater than initially predicted. Currently, the full cost of dam removal in Scotland for a non-engineered solution is approximately 60-80% acquiring the licence. This cost was absorbed by the Forth Rivers Trust as part of the organisational aim to initiate a culture of common-sense and financially responsible dam removals in Scotland.

The complexity of the weir’s ownership could potentially had been a showstopper, as the two riverbanks on the site had different owners. One side of the riverbank is owned by West Lothian Council, with the other riverbank’s owner untraceable despite extensive investigatory works. This caused a degree of financial risk: budget was spent carrying out preparatory surveys and planning removal, but all would have been for nothing if an asset owner had come forward and prevented the removal.

Ecological and community benefits
Observed benefits include the restored river connectivity and fish passage; fish were leaping the weir on day 5 of the removal works, having sensed a shift in the river. While scientific monitoring at the site post-barrier removal has not yet been possible, subsequent site visits have made apparent the clear difference to the Linhouse Water. The river channel has been renaturalised, as boulders and gravels previously impounded by the barrier have settled out into the channel. The river itself has also been diversified, changing from slow-flowing and almost featureless water to a river that can be heard and seen with diverse water features including riffles, pools, and runs, offering ecological benefits for invertebrates, fish, and all aquatic fauna. The 2-metre difference in height from upstream and downstream the barrier caused is long gone, with a steady gradient created by the movement of sediment during high river flows. The site is now passable to all species in most water conditions, and both looks and sounds like a vibrant, healthy water environment for wildlife and people to enjoy.

The site will be used to demonstrate to stakeholders the need for free-flowing rivers and will be visited occasionally to check up on the area to visually monitor changes to the river via drone flights. Such a site visit was undertaken on April 6-7, 2024, with a steering group from one of the Forth Rivers Trust’s projects, with staff who undertook the weir removal sharing their expertise.

Before & After photo pair

The removal site at Linhouse Water: (left) before and (right) after the demolition of the Morton Quarry Weir © Forth Rivers Trust

With many thanks to the Forth Rivers Trust for providing the information and the visuals presented herein.

Written by Foivos A. Mouchlianitis