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Background Scour is not a new phenomenon. However, the increasing frequency and intensity of extreme weather events, which at least in part as a consequence of climate change, has led to a number of bridge failures not just in the UK, but also across Europe, including: in the UK, a large number of bridges destroyed during the Cumbria floods in 2009 causing loss of life and extensive traffic disruption in Spain, the Margarola bridge, which failed in 2006 due to the interaction with the scour at a nearby bridge, causing two casualties in Portugal, the Hintze Ribeiro bridge in Castelo de Paiva, which collapsed in 2001 due to general degradation of the river bed because of dredging, causing 60 casualties. These events have acted as a salient reminder to asset owners/managers/ operators as to the vulnerability of aged infrastructure assets and that the design basis for more newly constructed works may not be as robust as intended. Challenges The challenge facing asset managers is that despite the undesirable consequences associated with structural failures at river crossings, it is rare that sufficient funds are made available to undertake all necessary inspection, assessment and improvement activities. It is because of limited budgets that difficult decisions are taken in order to decide how and where resources should be invested and, conversely, where they are not financially justified. Understanding risks along transport networks is fundamental to their operation and provides an evidence base to define management actions and strategies. Supporting decision making Work to support decision making through the development of a new framework and method of probabilistic scour risk assessment has been carried out by researchers at HR Wallingford as part of the Future Resilient Transport Networks (FUTURENET) project. This has been funded by the Engineering and Physical Sciences Research Council (EPSRC), as part of the Adaptation and Resilience to Climate Change (ARCC). FUTURENET addresses the issue of identifying vulnerabilities in transport infrastructure to climate change with a focus on the London-Glasgow transport corridor including highways and railways. It will contribute to assessing, in a quantitative and analytically rigorous way, the risks of scour failure at bridges. Decision makers will then be able to have greater confidence in the risk assessments on which they are basing their infrastructure investment decisions. The new methodology uses fragility curves to account for uncertainty as well as taking into account the protection around bridges (Roca and Whitehouse, 2012). The presence of protection works aims to change the relation between scour and the probability of failure of the infrastructure. Protection ‘delays’ the possible exposure of bridge foundations by controlling the channel position and increasing the hydraulic load needed to fail the protection. The methodology developed to estimate the probability of bridge failure due to scour at river crossings aims to be repeatable, as much as possible, independent of the user, and easy to update as more information or better knowledge becomes available. It does not aim to estimate the risk associated with a particular event, but instead to estimate all possible events in order to obtain an annual probability at each bridge site. The annual probabilities calculated for different climate change scenarios can then be compared to chosen thresholds of safety levels to establish the necessary management strategies. HR Wallingford’s project and that of other projects carried out in the UK and around the world are feeding into a CIRIA research project to revise the existing Manual on scour at bridges and other hydraulic structures (May et al, 2002), which was published over 10 years ago. 19 Figure 1 Failed bridge due to scour (courtesy HR Wallingford)


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