Bridges

Our changing climate is leading to patterns of increasingly extreme weather across the globe, with more intensive rainfall leading to increasing frequency of flood events that have historically been considered lower return periods occurrences. This higher frequency of severe flooding is having a significant impact on bridge structures in New Zealand. Structures crossing rivers in flood are subject to scouring which can undermine existing protections and expose these structures to the risk of damage, particularly those with existing vulnerabilities. Damage to these structures increases the risks to road users and threatens critical service infrastructure.

In aid of determining points of vulnerability, the New Zealand Transport Agency (NZTA) developed a scour screening process in the early 2000s to evaluate hazard exposure of structures. The National State Highway bridge stock comprising over 2750 bridges was screened using this process in around 2013, and from this a coordinated programme of scour improvements was undertaken for a number of years.

This paper will examine the efficacy of the NZTA scour screening process to predict scour damage and review differences in approach in selected other countries. It will also examine where updates to the process could be made using new technology to better predict scour damage, understand cost implications and to enable asset owners to utilise this data to understand their risk profile, and apply the screening process more broadly across networks with differing relative importance. We will examine case studies from previous events and failures; compare previous and retrospective scour screening results using prior processes and proposed improvements; and discuss how data from annual inspection processes could be incorporated to enable dynamic assessment and management of scour risk at a network level.