Articles | Volume 17, issue 8
Nat. Hazards Earth Syst. Sci., 17, 1393–1409, 2017

Special issue: Risk and uncertainty estimation in natural hazards

Nat. Hazards Earth Syst. Sci., 17, 1393–1409, 2017

Research article 11 Aug 2017

Research article | 11 Aug 2017

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

Rob Lamb1,2, Willy Aspinall3,4, Henry Odbert4, and Thorsten Wagener5,6 Rob Lamb et al.
  • 1JBA Trust, South Barn, Skipton, BD23 3AE, UK
  • 2Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK
  • 3Aspinall and Associates, Tisbury, UK
  • 4School of Earth Sciences, University of Bristol, Bristol, UK
  • 5Civil Engineering, University of Bristol, Bristol, UK
  • 6Cabot Institute, University of Bristol, Bristol, UK

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