A hybrid approach to forensic study of bridge scour

The Feather River Bridge on Route 20 in Northern California, USA, was damaged by scour during a relatively modest flow event in March 2011. The scour created a hole around the foundation which was nearly 30 feet (9·14 m) deep and which permanently reduced the pile capacity at the main channel pier, requiring an emergency contract to repair the damaged structure. Following the event, several studies were made to help explain the causes of the scour event, including a geomorphological survey of the bank erosion history causing the high degree of misalignment of the flow, a laboratory flume study to examine the evolution of the scour hole and three-dimensional computational fluid dynamics experiments for studying the decay and magnitude of the erosion forces for various scour depths. An additional goal of the modelling was to investigate why the scour ceased at 30 feet and to estimate the erosion forces in the scour hole at that depth.