Monitoring and simulation of bridge pier scour depth

Owing to deep slope, frequency of extreme rainfall, typhoon attacking and earthquake impacts, huge amount of sediment would be generated from mountain area, especially in Taiwan. Such geological and hydrological changing will affect river flow and sediment transport condition in a river basin. During Typhoon Morakot in 2009, extreme amount of rainfall triggered fierce flooding throughout Taiwan to cause hundreds of bridge piers, abutments, piers, decks and approach roads damaged, especially at central and southern Taiwan. Therefore, the Minchu Bridge in the Zhuoshui River Basin is selected as the study area in this study. In addition, the bridge safety issue is seriously discussed during flood event and bridge-scour problems attract considerable attention in Taiwan. The total bridge scour depth in front of a pier is affected by general scour, local scour, contraction scour, and bend scour. In general, the general scour is calculated by sediment transport equations and bend scour is considered by 2-D numerical model simulation. The general scour results from bed material transportation, which includes suspended load and bed load. The best general scour estimation from the calibration and verification processing are obtained using the bed load equation for the bed load in combination with advection dispersion equation for the suspended load in the study area. Therefore, a two-dimensional numerical model with sediment transport equations is applied to solve such kind of scour performance. It is about 1000 m in length for 2-D simulation domain. In addition, we also discuss several empirical formulas of local scour to find out the feasible one. We hope the prediction of bridge pier scour depth using numerical model coupled with empirical equations can provide valuable and in-time information for bridge safety affairs in the future.