Quantifying uncertainty and reliability in bridge scour estimations

The majority of the bridges in the U.S. National Bridge Inventory (NBI) are built over waterways. Many will experience problems with scour, bank erosion, and channel instability during their design life. A number of studies in the recent past have attempted to quantify the uncertainty in predicting these erosional processes, particularly in pier scour, and developing probabilistic estimates of scour as a means of incorporating uncertainty. However, none of these studies have examined the overall uncertainty in local pier or abutment scour in combination with contraction scour. This study quantifies the model uncertainty in commonly used scour equations as well as parameter uncertainty. The overall reliability of the scour equations is then assessed for the individual components of scour and combined scour. The results lead to a set of scour design factors that are based on the reliability of the design estimate.