Trends Summer 2017 - Page 13

Fighting the forces of nature When water levels rise, and bridges are at increased risk of damage or failure, scour countermeasures and plans of action are paramount By Jennifer Schmidt A n old saying states that “a person who overlooks water under bridge will find bridge under water.” It’s something that Rob Ettema, a civil engineering professor at Colorado State University in Fort Collins, has a vested interest in and has teamed For engineers and scientists studying with Ayres Associates to study for bridge safety and stability, these words the National Cooperative Highway ring especially true. And they serve as Research Program. Ettema and Paul an important reminder to routinely Clopper, Ayres’ director of applied be mindful of bridges’ vulnerability to technology, are principal investigators scour. of an ongoing research project involving contraction scour, a type of Scour – a naturally occurring process erosion that occurs when the flow where flowing water removes of a waterway’s natural channel is sediment from around bridge piers narrowed and picks up speed traveling and abutments – is recognized as through the bridge opening. Their the No. 1 cause of bridge failures in objective is to develop contraction the United States. Without adequate scour equations that will be used as design and countermeasures in place, future guidelines for risk-based bridge scour can destroy infrastructure and design in various hydraulic conditions. undermine bridge foundations. Ettema said bridge scour is an often overlooked – but critically important – issue to research and evaluate. “The way that the water can erode the bed level and the sides of the channel through the bridge waterway can lead to the instability and then failure of the bridge’s piers and abutments,” Ettema said. “The flow field varies over time and is often hard to forecast, so we need to continually develop better insight into what happens – and better predictive methods for bridge design.” Combatting crisis Scour vulnerabilities can yield catastrophic results, including bridge │13