Cross mill Weir, Scotland, UK

Weir removal to restore the Levern Water to pre-industrial conditions

The Levern Water
The Levern Water is a small river in East Renfrewshire, Scotland, UK. It sources in the Long Loch and runs through the towns of Neilston and Barrhead for 14 km before it joins the White Cart River near to Crookston Castle (Figure 1). The river facilitated the socio-economic growth of East Renfrewshire as it was the primal water source to power cotton and paper mills during the Industrial Revolution. As a result, the Levern Water was heavily modified.

Figure 1. The White Cart River catchment. The location of the Cross mill Weir in Levern Water is pointed by a red cross © SEPA

The Cross mill Weir
The Cross mill Weir was a 1.9-m high and 10.5-m-long barrier made out of concrete and sandstone blocks (Figure 2). It was located in Barrhead, a small town of ~18000 residents in East Renfrewshire, Scotland, 13 km southwest of Glasgow (Figure 1 & 3). It was constructed around 1860 to power Cross mill Print Works and remained obsolete for many years after the mill ceased to run.

Figure 2. The Cross mill Weir © SEPA

Figure 3. Location of the Cross mill Weir at Barrhead, East Renfrewshire, Scotland, UK

Cross mill Weir was the last remaining barrier to migratory fish on the Levern Water. Fish surveys conducted by Clyde River Foundation demonstrated that salmonids were present as far upstream as the weir, which was unsurpassable, and thus blocking fish from reaching spawning grounds further upstream (Figure 4). Evidence of otters at the area has also been found.

Figure 4. Salmon distribution on the Levern Water before the removal of the Cross mill Weir © Clyde River Foundation

Dam removal
To safely remove the weir, the entire flow of the Levern Water was diverted through a pipeline over land at a rate of 400 liters per second for two days (Figure 5). This provided safe access to excavator and work crews to the dry riverbed (Figure 5). During the demolition works, silt control occurred, and more than 20 tons of material were removed (Figure 6, Video 1).

Figure 5. Diversion of Levern Water’s flow prior to the removal of the Cross mill Weir © SEPA

Figure 6. (left) Silt control and (right) in river works during the demolition of the Cross mill Weir © SEPA

Video 1. Removal works of the Cross mill Weir © SEPA

The riverbed was reprofiled after the demolition of the weir to create a gentler slope (Figure 7), however this was light touch as the weir sat on bed rock. The removal works were completed in late October 2023 (Figure 8, Video 2), opening up 4 km of good quality spawning habitat to migratory fish and restoring the physical condition and ecological status of the Levern Water from POOR to GOOD (as assessed by SEPA’s River Basin Management Plan).

Figure 7. Reprofiling of the riverbed of Levern Water following the removal of the Cross mill Weir © SEPA

Figure 8. Removal site at Levern Water after the demolition of the Cross mill Weir © SEPA

The removal of the Cross mill Weir costed £271000 and was the final phase of a wider environmental regeneration and river restoration project aiming to restore the Levern Water to pre-industrial conditions and form an attractive green corridor between Barrhead and Glasgow. The first phase of the project was completed in 2022 at a cost of £2.8m and resulted in transforming an area of vacant and derelict land extending into the existing Calibar park and removal of another weir.

Video 2. Removal site at Levern Water on late October 2023, after the demolition of the Cross mill Weir © SEPA

The whole project was carried out through a collaborative partnership involving East Renfrewshire Council, Green Action Trust, Scottish Environment Protection Agency (SEPA), and was supported by the local community especially Carlibar Primary School and the Clyde River Foundation. Financial support was provided by SEPA’s Water Environment Fund, Scottish Government and the Open Rivers Programme, a Dutch grant giving foundation funded by Arcadia.

Challenges
Several challenges emerged and needed to be overcome during the removal of the Cross mill Weir. A delay in designing phase conducted by design consultants caused a later than planned start to works resulting in a very small in river working window (in Scotland in river working has to be authorised by SEPA and within a working period to coincide with the migratory fish spawning season usually end of May to end of September, this can vary slightly according to the water course). In fact, the work’s contractors came out of working in the river one day before the deadline. In addition, delivery timescale slippage caused by the need to source additional funding. This forced the weir demolition to be conducted at a period of exceptionally high rainfall, increasing the risk of the in-river works. The heavy rainfall prior to the works also caused a delay to the start of works as the large pumps needed for over pumping the river water had to be diverted for flood use elsewhere in Scotland. However, due to the collaboration of all involved parties, the project was completed on time and on budget and delivered all the desired objectives.

Valuable lessons were also learned during this project. For example, assessment of the pump capacity needed for over-pumping should be well oversized at watercourses that can be very flashy in nature, like the Levern Water. Also, changeable weather conditions should be taken into consideration when planning the timeline of such a project.

Ecological and community benefits
The initial aims of the Cross mill Weir removal were various and expected to have multiple outcomes in the habitat and biodiversity, water quality, and health and wellbeing of the local community, including:

• Salmonids, like Atlantic salmon, spawning above the former weir for the first time since the Industrial Revolution
• More resilient fish stocks in Levern Water on which otters can flourish and expand their territory further upstream
• Reduction of upstream sediment deposition, and thus flooding risk
• Improvement of water quality and advancement of river classification status from POOR to GOOD
• Reconnection of local community with the river which could potentially benefit their health, wellbeing and pride in their natural and built heritage
• Take advantage of this project to be used in educational programmes

Indeed, upon the completion of the weir’s demolition, many of those aims were achieved. Four km of good quality spawning habitat became available to migratory fish, which could lead to greater diversity in the local ecosystem. In fact, in early July 2024, evidence of salmon spawning upstream of the former weir was found, showcasing the ability of the ecosystem to recover swiftly upon restoration. Water quality and flow have also been improved and the silt deposition, as well as flooding risk, has been reduced.

In addition to the positive ecological and environmental benefits of the weir removal, the project of restoring the water course to its pre-industrial conditions has a positive impact also on the local community. The first phase of the project ignited public interest in the river and provided the opportunity to re-tell the forgotten history of the Levern Water. The local school children researched the historical significance of the river and created an art trail celebrating the river’s role in the town’s history. Moreover, the results of the weir removal have been very well received by the local community.

The long-term effects of the removal will be monitored by SEPA and the Clyde River Foundation in the years to come. Finally, the Cross mill Weir removal is planned to be showcased by the project’s partners at various forums and conferences and as a case study to inspire similar barrier removal projects in the country.

Before & After photo pair

The removal site at Levern Water: (left) before and (right) after the demolition of the Cross mill Weir © SEPA

With many thanks to Lucie Stewart and SEPA for providing the information and the visuals presented herein.

Written by Foivos A. Mouchlianitis