Assessing the risk to the coastal and rural road network in Scotland due to the effects of storms and extreme rainfall events

One of the key challenges for Scottish transport infrastructure is the identification and assessment of assets at greatest risk to damage from landslides, storms and flooding. This is particularly the case with the vulnerability of the rural and coastal road network. The Scottish Climate Change Adaptation Framework (Transport) states that the location and design of new infrastructure, must take account of an increased likelihood of risks from flooding and landslides. Many coastal areas already appear to be experiencing increased intensity of storms and extreme rainfall events and recent high profile events (e.g. inundation of A78, Skelmorlie, extensive damage to vital roads and causeways in the Western Isles, landsliding at Stonehaven and the repeated disruption along the A83 at the Rest and be Thankful, Argyll and Bute attest to the need for an accurate assessment of those areas at greatest risk and for the implementation of potential mitigation measures. Adaptation Scotland provides a wealth of existing science, data and advice on how to adapt in the face of increasing change, but there is a need to develop robust tools for using this to assess the corresponding risk and economic impact for effective whole-life asset management.

The aim of the project is therefore to develop a robust risk management tool, easily utilized by asset managers to assess threats to rural road transport assets in Scotland that are likely to be at risk from the effects of extreme rainfall and storms and differing future climate change scenarios. This will be determined by the following objectives:

- Adaptation of an existing framework for landslide hazard assessment through the incorporation of recently-developed datasets to allow application also to flooding/coastal geohazards;
- Production of diagnostic criteria to assess the nature of the different hazards (these include susceptibility to the various hazards and the spatial relation to the asset or road),
- Analysis of the risk posed to key areas of the network infrastructure (local and trunk roads) by means of an assessment of the elements at risk (road and road users) and their vulnerability within a multi-hazard environment;
- Assessment of economic impact to inform climate change adaptation plans and decision making for stakeholders at various levels from transport authority to local authority. Two case studies will be examined: (i) A78 Shore Road area and (ii) North and South Uists and Benbecula with island-linked causeways providing vital access to the Western Isles.

The stakeholder is Transport Scotland.

Keywords. extreme events, adaptation, resilience, management tool.

The outcome of this project will be a new management tool to assess the risk to rural and coastal roads from a range of geohazards and impacts on the transport network complementing existing tools for assessing risks (e.g.landslides), and therefore provide an additional 'tool in the toolbox' for infrastructure asset management. This tool will have transformative impacts, allowing multi-hazard impacts to be catered for in the design of new infrastructure and maintenance of existing infrastructure. The net asset value of the 3,200km Scottish trunk road network is estimated at around £15bn with an annual maintenance spend of around £111M (excluding capital spend and expenditure on M6, M77 and M80 DBFOs/PPIs). The new tool will allow maintenance spending to be better prioritized over the medium to long term and help safeguard this vitally important national asset. The tool also will be of value to Transport Scotland and Local Authorities in justifying increased road maintenance and capital spend in the light of climate change and geohazards more generally.

The benefits of the tool will be demonstrated primarily through case studies. We will explore with TS the different adaptation actions they would take with the additional knowledge that the tool provides. The consequences of these actions would be modelled (see project description) to estimate delay and maintenance cost savings. We would also qualitatively explore other benefits from these actions, and more resilient transport networks. It may be possible to extrapolate the cost savings if the tool was applied to the entire road network.

In addition we will discuss with TS potential applications of the information provided by the tool, for example in funding applications and budget allocations, or in raising awareness of climate change implications internally within their organisation. An assessment of the potential impact of the tool will form part of the Innovation Report and be presented at the ERIIP dissemination event.