Field Measurements and Simulation of Bridge Scour Depth Variations during Floods

An understanding of bridge scour mechanisms during floods in a fluvial river is very important for cost-effective bridge foundation design. Reliable bridge scour data for flood events are limited. In this study, field experiments were performed at the Si-Lo Bridge in the lower Cho-Shui River, the longest river in Taiwan, to collect scour-depth data using a sliding magnetic collar, a steel rod, and a numbered-brick column. By separating each scour component, a methodology for simulating the temporal variations of the total scour depth under unsteady flow conditions is proposed. The proposed total-scour model integrates three scour components, namely general scour, contraction scour, and local scour. The collected field data, comprising both general scour and total scour depths, are used to validate the applicability of the proposed model. Based on the peak flow discharges during floods, a comparison of the local scour depths calculated using several commonly used equilibrium local scour formulas indicates that most equations may overestimate the local scour depth.