Insights from Depth-Averaged Numerical Simulation of Flow at Bridge Abutments in Compound Channels

Abstract

This study presents findings from two-dimensional depth-averaged flow models used to investigate distributions of flow velocity, unit discharge, and boundary shear stress associated with flow around spill-through bridge abutments, a very common form of bridge abutment. Design engineers often use such flow models to determine the distribution of flow through bridge waterways and to estimate peak magnitudes of flow velocity, unit discharge, or boundary shear stress for use in design estimation of abutment scour depth. The findings show how abutment flow fields, dominated by flow contraction around the abutment, adjust in response to variations of abutment length, floodplain width, and main-channel dimensions. The adjustments alter the magnitudes of amplification factors for depth-averaged velocity, unit discharge, and bed shear stress in the abutment vicinity; amplification factor for velocity is the ratio of maximum velocity to mean approach velocity (on the upstream floodplain or in the main channel). They also alter the distance from the abutment toe to the locations of peak values. This study covers a much broader range of abutment lengths, floodplain widths, and channel dimensions than heretofore reported in the literature.