Update on Measures to Protect Against Rockfalls on B8035, Gribun, Mull
Argyll and Bute Council · 18 December 2025
Back to Environment, Development and Infrastructure Committee — 18 December 2025 and its agenda
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ARGYLL AND BUTE COUNCIL ENVIRONMENT, DEVELOPMENT AND INFRASTRUCTURE COMMITTEE ROADS AND INFRASTRUCTURE 18 DECEMBER 2025 UPDATE ON MEASURES TO PROTECT AGAINST ROCKFALLS ON B8035, GRIBUN, MULL 1.0 EXECUTIVE SUMMARY 1.1 The B8035 at Gribun links a number of remote communities and is a popular tourist destination. It is also a key location for local events such as the Mull Rally. 1.2 In July 2025, the first of three significant rockfalls occurred on the B8035 at Gribun, Isle of Mull. 1.3 Further rockfalls followed in August and September, prompting immediate closure of the road. 1.4 Since closure of the road, drone and geotechnical surveys have been conducted on the hillside above the road. The reports arising from these surveys have been received by the council and are currently being evaluated by council officers 1.5 A number of options have been identified by these reports ranging from “do nothing” to the installation of rockfall fences, and scaling of loose material from the rock face. 1.6 This report explores these options, their cost and the impact of the closure on local communities 1.7 RECOMMENDATIONS Members of the Environment, Development and Infrastructure Committee are invited to - 1. Note the options outlined in Table 4.1, and agree that officers continue to work with partners to identify an option that keeps risk as low as reasonably practicable having regard to:
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i. the likelihood and ii. the impact of any rockfall versus the cost of prevention. 2. Note that a further update report will be brought to a future EDI Committee as soon as a preferred option and costings have been identified.
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ARGYLL AND BUTE COUNCIL ENVIRONMENT, DEVELOPMENT AND INFRASTRUCTURE COMMITTEE ROADS AND INFRASTRUCTURE 18 DECEMBER 2025 UPDATE ON MEASURES TO PROTECT AGAINST ROCKFALLS ON B8035, GRIBUN, MULL 2.0 INTRODUCTION 2.1 The B8035 at Gribun links a number of remote communities and is a popular tourist destination. It is also a key location for local events such as the Mull Rally. 2.2 The road has been vulnerable to rockfalls since it was built, although these have not been recorded until recently. 2.3 In the summer of 2025, three rockfalls / landslides were reported to the council. The road has been closed since August of this year to protect road users from serious injury, and to allow officers to develop long term options for the safe use of the road. 2.4 This report outlines these options, as well as the impact that the current road closure is having on nearby communities 3.0 RECOMMENDATIONS 3.1 Members of the Environment, Development and Infrastructure Committee are invited to - 1. Note the options outlined in Table 4.1, and agree that officers continue to work with partners to identify an option that keeps risk as low as reasonably practicable having regard to: iii. the likelihood and iv. the impact of any rockfall versus the cost of prevention. 2. Note that a further update report will be brought to a future EDI Committee as soon as a preferred option and costings have been identified.
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4.0 DETAIL 4.1 Since the council closed the B8035 at Gribun on the Isle of Mull in August 2025, geotechnical surveys have taken place to identify • Potential causes of the rockfalls and landslides, • The frequency at which these happen, • The potential impacts that they could have on road users, and • The preventative measures that should be considered, and their cost. 4.2 We have been working with local famers and the NFU, and local members have been kept informed, particularly regarding impacts on local events such as the Mull Rally. Public updates are provided via the council’s website and social media channels. Engagement with residents and businesses continues to ensure awareness of the closure, the reasons for it and the diversion route. 4.3 In the meantime, a diversion has been put in place via the A849 Kinloch– Craignure–Salen route. This route is approximately 22 miles long. 4.4 The implementation of preventative measures is complicated by the remote location involved, and the confined nature of the site being located next to the sea and at the bottom of a cliff. 4.5 The most recent report by our geotechnical consultants, Atkins Realis, was received by the council on 12th November 2025. 5. The updated hazard modelling, incorporating rockfall modelling and site-specific observations, confirms that the estimated frequency of rockfalls poses a risk level that is on the boundary of Tolerable / Unacceptable. Under certain conditions or circumstances such as increased rainfall or increased vehicle movements, this is likely to move into the Unacceptable level of risk, especially in areas: • That may have higher rockfall frequency, or • Where the cliff face is directly adjacent to the carriageway with reduced lines of sight. 4.6 The quantitative risk assessment is preliminary and there are a number of factors that have been simplified, such as annual rockfall frequency and some factors such as drivers' reaction to avoid fallen rocks that have not been taken into account. Mitigation options which are likely to reduce the level of risk to an acceptable level have been presented in Table 4.1 below.
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4.7 To take the project onto the next stage, Atkins Realis recommend that the council undertakes a review and determines the most appropriate two remedial options or combined options (e.g. signage and scaling of specific areas) that manage our risks at a tolerable level. These two options can then be progressed to enable a budget to be set for the project, and detailed consultation with appropriate stakeholders. The most beneficial option, in terms of cost, programme, and risk reduction could then be taken forward to the next stages of implementation. Table – Summary of options Mitigation Option Effectiveness Estimated Cost Long term maintainability Estimated timescale Reopening with additional signage Low – unlikely to reduce risk and liability Low – limited to cost of signage Limited maintenance required Weeks / months Road closure with local access Removes the risk to the public accessing the site with vehicles. Risk remains to those accessing on foot or cycling. Cost of permanent barrier installation at each end of closure plus cost of implementing new Traffic Regulation Order (TRO) Limited maintenance required. Ongoing monitoring and staffing required to close the barrier At least 3 months, dependant on TRO process Road closure during rainfall events Low without further rockfall monitoring to increase understanding of relationship between weather and rockfalls / landslides Costs for developing rockfall management plan and installing barrier. Staffing costs for monitoring and closing barrier Limited maintenance required. Ongoing monitoring and staffing required to close the barrier Weeks / months Earthwork bund Not considered due to expansive prohibitive costs Rockfall fences – whole slope High – reduces likelihood of detached rocks reaching the road £3.6 million with subsequent maintenance and inspections costs Regular inspections and maintenance following rockfall events 1 – 2 years Rockfall fences - targeted Moderate – reduces likelihood of detached rocks reaching the road within the assumed higher frequency area £1 million with subsequent maintenance and inspections costs Regular inspections and maintenance following rockfall events 6 – 8 months Rock Stabilisation Netting – Whole slope High – prevents detached rocks from reaching the road £65 million with subsequent maintenance and inspections costs Regular inspections and maintenance following rockfall events 1 – 2 years Rock Stabilisation Netting – Targeted (example 500m) Moderate - prevents detached rocks from reaching the road £20 million with subsequent maintenance and inspections costs Regular inspections and maintenance following rockfall events 6 – 12 months Scaling – full slope High – reduces the number of detached rocks thereby reducing risk £2 million with subsequent regular scaling and inspection work costs High cost of initial scaling. Required further work at regular intervals. However, this will be significantly lower than initial costs 1 – 2 years for initial inspection and scaling Scaling - targeted Moderate – the number of detached rocks thereby reducing risk within assumed higher risk areas £500,000 with subsequent regular scaling and inspection work costs High cost of initial scaling. Required further work at regular intervals. However, this will be significantly lower than initial costs 6 – 12 months
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4.8 It should be noted that the proposals, costs and timescales are extremely high level and are only indicative. Further work will be required by council officers working in conjunction with specialist quantity surveyors to develop preferred options and costings. In the meantime, the road will remain closed until a final decision is made on implementation of a preferred option. 5.0 CONCLUSION 5.1 Local feedback has been received which outlines that the community and specifically the local farmer believe that the Council have been overprotective in the closing of the road and there has been instances where the road closure barriers have been removed and vehicles are using the road despite it being closed. This has been reported to Police Scotland for further investigation. 5.2 The council is taking a safety-first approach to addressing the issues presented by the rockfalls and landslides at the cliffs at Gribun. The closure of the B8035 is a necessary precaution while expert assessments are completed. 5.3 The council is committed to identifying a solution that balances risk, affordability and access for the communities affected. In the meantime, diversions and community engagement are being maintained to minimise disruption. 6.0 IMPLICATIONS 6.1 Policy – none. 6.2 Financial – the cost of undertaking the surveys completed to date will be £22,400. No further financial commitments have been made at this time, and will be dependent on a preferred option being identified and agreed. 6.3 Legal – the principal legislation covering road safety in Scotland is the Roads (Scotland) Act 1984. This Act defines management and maintenance obligations as follows: a. Maintain all public roads Councils must manage and maintain roads listed in their list of public roads. The Act Includes powers to reconstruct, alter, widen, improve, or renew roads. b. Risk-based maintenance approach While there is no statutory maintenance standard, councils are expected to adopt best practice (e.g., SCOTS guidance and UK Code of Practice) for inspections and repairs. It recommends risk-based regimes for addressing defects like potholes, prioritising based on safety risk rather than fixed intervention levels. 6.4 HR – none. 6.5 Customer Service – stakeholders including elected members and
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communities have been kept up to date on the council’s actions to address the issues at Gribun via a dedicated page on the council’s website. 6.6 Risk – this is currently being addressed using the powers and responsibilities within the Roads (Scotland) Act 1984 as identified in paragraph 6.3. 6.7 Climate Change – whilst there is reference in the geotechnical report by Atkins Realis to the impacts that climate change will have on future incidents at Gribun, the action currently being taken have no direct impact on the council’s climate change activities. 6.8 Fairer Scotland Duty – none. 6.9 Equalities - protected characteristics – none. 6.10 Consumer Duty – none. 6.11 Island Communities – none at this time. 6.12 Children’s Rights and Wellbeing – none. Kirsty Flanagan Executive Director with responsibility for Development and Infrastructure Services Policy Lead John Armour 30 November 2025 For further information contact: Andy Summers, Head of Roads and Infrastructure Services Hugh O’Neill, Network and Standards Manager APPENDICES Appendix 1 – Geotechnical Report from AtkinsRealis, 12 November 2025