Articles | Volume 17, issue 8
Research article
11 Aug 2017
Research article |  | 11 Aug 2017

Vulnerability of bridges to scour: insights from an international expert elicitation workshop

Rob Lamb, Willy Aspinall, Henry Odbert, and Thorsten Wagener

Abstract. Scour (localised erosion) during flood events is one of the most significant threats to bridges over rivers and estuaries, and has been the cause of numerous bridge failures, with damaging consequences. Mitigation of the risk of bridges being damaged by scour is therefore important to many infrastructure owners, and is supported by industry guidance. Even after mitigation, some residual risk remains, though its extent is difficult to quantify because of the uncertainties inherent in the prediction of scour and the assessment of the scour risk. This paper summarises findings from an international expert workshop on bridge scour risk assessment that explores uncertainties about the vulnerability of bridges to scour. Two specialised structured elicitation methods were applied to explore the factors that experts in the field consider important when assessing scour risk and to derive pooled expert judgements of bridge failure probabilities that are conditional on a range of assumed scenarios describing flood event severity, bridge and watercourse types and risk mitigation protocols. The experts' judgements broadly align with industry good practice, but indicate significant uncertainty about quantitative estimates of bridge failure probabilities, reflecting the difficulty in assessing the residual risk of failure. The data and findings presented here could provide a useful context for the development of generic scour fragility models and their associated uncertainties.

Short summary
Scour (erosion) during floods can cause bridges to collapse. Modern design and maintenance mitigates the risk, so failures are rare. The residual risk is uncertain, but expert knowledge can help constrain it. We asked 19 experts about scour risk using methods designed to treat judgements alongside other scientific data. The findings identified knowledge gaps about scour processes and suggest wider uncertainty about scour risk than might be inferred from observation, models or experiments alone.
Final-revised paper