Analysis of Estimated Scour vs Inspected Scour on a Bridge after Hurricane Maria, and their Impact on the Puerto Rico Bridge Program

Abstract

Bridge scour is considered the main reason for bridge failures due to the holes that can form and compromise the structure stability. Federal regulations require all proposed bridges to be designed for scour resistance and all existing bridges to be evaluated for scour vulnerability. Scour evaluations are typically based on the 100-year recurrence flood event. Bridges determined to be unstable due to observed scour or assessed high potential for scour are deemed scour critical. Various equations to evaluate scour are available, however many of them are considered conservative and leading to overestimation of the scour depths. The pass of Hurricane Maria over Puerto Rico triggered catastrophic flooding in the magnitude of a 100-year recurrence flood and higher, hence replicating the conditions for which bridges are evaluated. To analyze evaluated against observed scour, a bridge within Maria’s track was inspected and compared as a case study to its evaluation results. The outcome showed that the equations may have overestimated the scour depths, given no scour was found at the bridge; also implying that this overestimation could have an impact on the Puerto Rico Bridge Program, which currently has 495 scour critical bridges, all requiring flood monitoring and, consequently, greater resources. Key Terms – Bridge Scour, Flood Monitoring, Hurricane Maria, Scour Critical Bridges.