An Approach to Overtopping Assessment for a Resilient Railway at Dawlish, UK

Following regular disruptions to the Southwest rail network, especially during the storm events of 2014, Arup was appointed by Network Rail (NR) to complete a feasibility review, optioneering and single option development for the Dawlish railway section from Colonnade to Coastguards (C2C) including Dawlish Station and Dawlish Water River basin. The objective of the project was to assess resilience options to wave overtopping, determine feasibility of each option and analyse their respective advantages to select the most appropriate option. The criteria included resilience performance, sustainability, buildability, programme, adaptation and whole life cost. This paper focuses on wave overtopping as a key driver of the design process with important lessons learned from a large physical modelling campaign. A staged approach was developed; it involved development of specific criteria for the assessment of the wave overtopping performance; analytical estimations of overtopping performance based on Eurotop, 2018; testing in a 2D physical model to assess the sensitivity to varying seawall configurations; testing of the initial scheme in a 3D physical model; design optimisation in the 3D physical model; tests of the existing/’do nothing’ in 2D or 3D to highlight the benefits of the proposed scheme; development of an adaptive design.