Stream Stability and Scour at Highway Bridges

ABSTRACT A 1987 bridge failure in upstate New York, which cost ten lives, resulted in establishing a national (U.S.) program that requires each state to evaluate all their bridges over water for vulnerability offailure from erosion of their foundations (scour). This evaluation is to be carried out by an interdisciplinary team consisting of hydraulic, structural, and geotechnical engineers. This evaluation is in addition to the National Bridge Inspection Program that requires the states to inspect all bridges every two years to determine their structural integrity. To aid the states in the evaluation program two publications were issued, HEC-18 entitled, “Evaluating Scour at Bridges” and HEC-20, “Stream Stability at Highway Structures.” These publications give guidelines for doing the evaluations; give equations and methods for computing scour; suggest a design philosophy that bridges should be designed using the flow for a 100–year return period flood and to withstand the effects of scour from a superfloo...