Railway bridge failure during flooding in the UK and Ireland

Abstract

A review of accident reports and other sources has shown there have been 15 fatalities, and perhaps 4–5 times that number of injuries, which can be attributed to structural failure during flooding on the railway system in Britain since the 1840s. The resulting present-day economic damage is estimated to be at least £300 million. Bridge failure due to flooding is most commonly associated with ‘extreme’ but not necessarily ‘very rare’ floods; the average event rarity associated with catastrophic failure is 1 in 160-year return period, but the range of 200–250 years includes most flood-related failures. Undermining of abutments and piers by scour is the most common form of failure of bridges. The remaining failures can be attributed to six other failure sequences which are currently not adequately addressed within the existing procedures. Of these six, debris collection resulting in enhanced local scour and the location of structures in rapidly responding catchments are considered the most significant. It is recommended that the design flood for scour assessment and protection design should be based on a 200-year return period flood event. A higher value (of 1000 years) may be appropriate for structures with a particularly high consequence of failure.