The impact of future sea-level rise on the London-Penzance railway line

Abstract

The coastal section of the London to Penzance railway line (Dawlish-Teignmouth) lies very close to sea level and has been susceptible to frequent closure during high seas and storm events. As the main railway connection for the southwest of England to the rest of Great Britain, it is a vital transport link for the Devon and Cornwall economy. Current understanding of future sea-level rise in the region is compromised by a lack of reliable geological data on which to establish accurate future sea-level projections. Furthermore, the impacts – in engineering and economic terms – of potential sea-level change on the long-term functioning of the main railway are unclear, and future policy making and planning are compromised by a similar gap in scientific knowledge. The central aim of this thesis is to establish the extent to which future sea-level changes will impact upon the Southwest’s main railway line. This aim carries three objectives: (1) to establish accurate sea-level trends over the last 4000 years (late Holocene) in order to validate geophysical models used in current future sea-level projections in the southwest of England; (2) to establish the likely impacts of future sea-level change on the functioning of the Dawlish-Teignmouth railway line; and (3) to integrate climate and socio-economic futures (scenarios) in an internally consistent manner for future use in regional policy debates. In addressing these objectives, we estimate that during the last 2000 years the coast of south Devon has subsided at a rate of ~1.1 mm/yr, generating a relative sea-level rise of ~0.9 mm/yr. The geophysical model (used to determine regional sea-level projections) underestimates the geologically estimated coastal subsidence rate by only 17%, which would generate an additional sea-level rise, compared to predicted values, of 0.014 m by 2100. Based on an empirical trend between increases in sea-level changes and rail functioning during the last 40 years, the corrected sea-level projections provide input for establishing future days with line restrictions due to overtopping on the Southwest Mainline. Impacts to both the Southwest economy (e.g., rail users) and the infrastructure owners have been determined, and integrating these forecasts with socio-economic scenarios (SES) has highlighted the important interaction between climate and socio-economic trends and future vulnerability. In a worst case scenario (e.g., high emissions), rail services are predicted to be disrupted (on average) for around 35% of the winter by 2060. By this stage, the cost of these disruptions will have exceeded the capital needed for constructing a new alternative inland route.