Ayrshire Rivers Trust recently secured funding for restoration work on the Mauchline Burn (a.k.a. The Chalk River) with the ultimate aim of reducing silt and nutrient inputs and restoring a functional trout and salmon population within this small watercourse. In recent years, the burn has suffered from repeat pollution incidents (from more than one source) and it has been more than a few years since any salmonid fish have been found alive. A burn of this scale should be capable of supporting both trout and a few salmon particularly in the lower third but in reality, poor water quality has rendered it virtually fishless by 2024 (bar a few sticklebacks). This situation is not uncommon in rural Ayrshire where burns that flow through agricultural land are often impacted by the land use and inputs. The length of the burn accessible to fish is relatively short at around 3 miles, by which time is is more suitable for trout than salmon. Upstream of this point, the burn is heavily modified (straightened along field margins and culverted under farm steadings and roads etc.). However, this upper section is where much of the silt and nutrient inputs arise and the project includes measures that will hopefully address the worst of these issues.
Funding from the Wild Salmon Fisheries Fund (circa £17,000), a contribution from the River Ayr DSFB (£1,500) and considerable resource inputs from Ayrshire Rivers Trust means that around £23,000+ is currently being invested into improving this burn. Work includes bank stabilisation in areas where the burn is highly mobile and also erecting livestock fencing that will immediately reduce nutrient and silt inputs. Silt is a major issue with this burn and there has been a constant movement of this from land to the burn, to the River Ayr for decades. In this case, livestock access drives both nutrient enrichment, silt inputs and erosion. This excessive silt load only serves to reduce spawning potential within the burn and on the Ayr downstream of the confluence. Enrichment causes eutrophication, reducing oxygen levels particularly in summer months impacting fish survival but also has other negative consequences on coastal bathing water quality and tourism for the area. Addressing problems such as these will only help the Ayr catchment improve.
Apart form their planned work, Ayrshire Rivers Trust staff performed some unexpected restoration work after discovering some straightening had taken place just a few weeks ago. Modifications of this type exacerbate silt problems and leave banks prone to erosion for decades. River engineering should always follow the Controlled Activities Regulations guidance and SEPA’s General Binding Rules. Where in doubt, the best course of action for landowners or contractors is to speak to SEPA licensing team or independent consultants such as the Trust or farm advisers prior to undertaking any such work. In this case, the Trust considered their options and decided to use green engineering techniques to repair the damage concurrent with their planned project works as leaving this to degrade further would render their aims useless. This was generous of the Trust as they ultimately bore the financial cost of these repairs and that was not insignificant.
Unauthorised bank works that cause multiple issues for bank stability and ecology. Silt smothers the natural substrates as there is virtually no flow to move it as the bed is over wide and shallow
The burn is over wide and shallow as a result if this work. The knock on impacts reduce fish spawning and survival and the habitat is unsuitable for a diverse invertebrate population that should be present.
This repair work used root plates and large woody debris sourced on site, all put in place using a large excavator. As the burn had been left over wide with reduced flow velocities, it was reinstated to the original width using brash and large woody debris, which achieved more natural flow regime. The bare soils were seeded. Hopefully there will be a rapid recovery of vegetation and stability in this section. The DSFB appreciates ART’s quick response and intervention.
Repairing an eroding section of the bank to protect an existing fence that otherwise would soon be left hanging. Root wads and large woody debris were built into the bank before it was reprofiled to better resist erosion. Just adding soil would not achieve the desired results. Having a large machine for extra reach allowed all work to be completed without damage to the river bed. Sedimats provided effective silt protection downstream of the work area
Protecting the toe of the bank using willow logs staked into the bed and bank so they can’t move
Brash faggots and coir geotextile membrane will protect the bank until it recovers (on the left bank) while on the right, these logs will prevent similar erosion occurring.In a few weeks both banks should have revegetated and the risk erosion should reduce. As the silt clears, the courser sediments will be exposed and silt should be trapped in the brash bundles adding strength to the toe of the bank. Already in this image, the fine silt that coated the bed has moved and once inputs reduce through fencing and other engineering upstream, the habitat should recover and support fish
Phase 1 of the project was completed last week under the Controlled Activities Regulations and SEPA’s General Binding Rules and didn’t involve any work to the bed or any section of banks over 10m in length. Trust staff carefully reprofiled eroding banks where there was likelihood of imminent collapse. This work was designed to be ‘light touch’ and used green engineering techniques to ensure banks not only stabilise but also rebuild by trapping fine sediment in the brash bundles they installed at the toe of the banks. These techniques have worked well elsewhere so should help here. Another technique utilised was the installation of root wads in the most severely eroding and undermined bends. Large root wads (plates) secured with fresh cut willow stakes will add stability and provide places of refuge for fish. Fortunately there was a pile of roots already on site and this helped not only the restoration but cleared up farmland too. Coir and biodegradable geotextile membrane were added to cover the bare slopes and is held in place with potato starch pegs. Willow cuttings were used in strategic locations and once developed, they should provide bank protection for decades to come. This is a modern and approved approach to instability issues and can bring huge benefits to rivers and wildlife.
A severe undercut where collapse seemed imminent. This was resolved by driving 3 large root wads into the eroding face and securing them with willow stakes. Similarly brash faggots were added to the toe of the bank to trap fine sediment and rebuild the bank from the bed up. It is surprising how quickly these brash bundles become filled with silt locking it up for years to come Careful placement of large root wads, brash faggots and large woody material should prevent this bend eroding further by protecting the fine alluvial soil from the force of the flow. A new fence will be erected shortly to help the burn stabilise. Only the most severe hanging banks were reprofiled in any way
Deliberately light touch repairs were performed with only overhanging sod being removed. The previous collapsed turves remain in place and are stable at the toe of the bank and these were planted with willow cuttings that should offer permanent stability and shade in a short space of time
Phase 2 of this project starts next week with livestock fencing going up to help reduce trampling grazing pressure and any nutrient inputs. The web site will be updated once ART complete phase 2 of their project and over the next few years as the habitat and fish population recovers.
All work was performed exclusively by Ayrshire Rivers Trust staff. Images are provided courtesy of the Trust who retain copyright. Anyone seeking advice on river engineering works can contact them at their office – 2 Crosshill Cottages, near Mauchline. KA5 5HJ or call 01290 518130. Ayrshire Rivers Trust is a Scottish Registered Charity.
