Adaption in Practice
The following case studies from the VLOG demonstrate the practical delivery of climate adaptation best practice, showing how risk-based approaches are being applied to manage localised climate impacts and strengthen infrastructure resilience.
Case Study A: All North-West 4 Rock Slopes
The “All NW 4 Rock Slopes” project was made up of four individual sites within the North-West trunk road unit comprising of the following locations: A85 Loch Awe, A82 Corran Ferry, A830 Loch Eilt and A830 Rannochan. Each of these sites had experienced unstable slopes leading to rockfall onto the TRN.
The likely failure mechanisms at all sites appear to be linked to the detachment of overhanging or partially loosened blocks, with root penetration into discontinuities acting as a key contributing factor. At all locations, heavy rainfall and associated build-up of water pressures may have exacerbated instability also due to the potential for sudden weather-related changes that can rapidly accelerate slope failure.
The works comprised of vegetation clearance, scaling of loose rock, and installation of rockfall protection systems. At A82 Corran Ferry, face support netting (25m x 11m) was installed following rock removal between retaining walls. At A85 Loch Awe, vegetation was cleared and loose rock scaled from a previously failed netting area. At A830 Loch Eilt, stabilisation included removal of boulders, scaling, and installation of both rockfall drapery (12m x 20m) and face support netting.
Targeted night closures were carried out to safely remove unstable boulders using netting, Nonex, and 50-tonne airbags. At A830 Rannochan, two unstable blocks were controlled and removed, with all material safely disposed of offsite.
The scheme was constructed between 24th February 2025 and 17th July 2025, with a total cost of approximately £315,000. By integrating future climate projections into the prioritisation and design process, the project not only addressed the immediate operational challenges of slope instability and rockfall onto the TRN, but also strengthened the slopes to withstand future extreme weather events, improving long-term resilience.
Case Study B: Crimond Carriageway (A90)
A 500-metre stretch of the A90 east of Crimond was found to have no formal drainage infrastructure, instead draining directly onto the adjacent verge. This resulted in persistent surface water flooding on the carriageway during rainfall events, creating significant safety concerns. The property on the northbound side regularly experienced flooding due to overflow from the adjacent ditch network, with the southbound field frequently ponded and encroached onto the carriageway, prompting multiple complaints and reports of disruption.
The initial proposal was to install a new carrier pipe within the northbound verge, directing flow down the access road at the eastern end of the scheme and out falling into the ditch network downstream of the affected property. However site visit investigations and discussions with the property owner revealed that that there was very little flow within the ditch. The water level remained at half capacity weeks after significant rainfall, suggesting limited flow likely caused by shallow topography and elevated water levels in the nearby loch. These issues rendered the proposed new connection unfeasible, and a direct outfall to the loch was also ruled out due to topographical limitations.
Instead, a revised solution was developed involving the installation of three separate infiltration systems within the southbound verge. These systems were spaced with breaks between to increase the upstream attenuation and were designed to allow a future connection between the systems, and an outfall into the ditch network should subsequent improvements be made. To further mitigate flooding in line with the increased rainfall marked by climate projections, on-site material was used to construct a bund around the lowest point of the field, increasing storage capacity. Additionally, a controlled overflow was installed to enable gradual discharge preventing overtopping onto the carriageway.
This solution avoided trenching through the carriageway, which had been resurfaced the year prior, preserving recent investment and minimising disruption. Construction works were completed in March 2024, with a total budget spend of approximately £93,000. The scheme demonstrates the importance of site-specific investigation and adaptive design in delivering effective, climate-resilient drainage solutions.