Stochastic Assessment of Scour Hazard

David Flores-Vidriales,Dante Tolentino,Roberto Gómez

doi:10.3390/w14030273

David Flores-Vidriales, Dante Tolentino + Show 1 more

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https://doi.org/10.3390/w14030273

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Abstract

Scour is the most frequent cause of bridge collapses in Mexico. Bridges located along the Mexican Pacific coast are exposed to extreme rainfall originating from tropical storms and hurricanes. Such environmental phenomena trigger sediment loss, which is known as scour. If maintenance actions are not taken after scouring events, the scour depth increases over time until the bridge collapses. A methodology to estimate the scour hazard considering both the scour–fill interaction and the Monte Carlo simulation method is proposed. The general extreme value probability distribution is used to characterize the intensity of the scouring events, the lognormal distribution is used to characterize the sedimentation process (fill), and a homogeneous Poisson process is used to forecast the occurrence of both types of events. Based on the above, several histories of scour–fill depths are made; such simulations are then used to develop time-dependent scour hazard curves. Different hazard curves associated with different time intervals are estimated for a bridge located in Oaxaca, Mexico.

Highlights

A bridge built over a river creates an obstruction to the water flow, changing the local flow field
This paper aims to propose a methodology to estimate scour hazard curves considering the following: (a) a preprocessing stage to fix missing data issues using data augmentation, (b) an information criterion for the probability distribution selection, and (c) the interaction of scour and fill events through time
Some notable differences are as follows: (a) SRICOS-EFA does not take in to account every event for the scour accumulation, and in a similar way a shear threshold is needed to produce scour. (b) It relies on average daily discharge produced by an autoregressive moving integrated average model (ARIMA) model, which has limitations in dealing with outliers. (c) It does not take in to account the accretion process

Summary

Introduction

A bridge built over a river creates an obstruction to the water flow, changing the local flow field. The erosion around the obstruction is accelerated due to the following three variables: (a) a velocity surge, (b) a difference in pressure between upstream and downstream areas produced by the perpendicular action of the flow, and (c) the generation of vortices. Scour begins when a certain level of shear stress, known as critical Shields stress, is reached. The sediment at the river bed lifts due to the action of vortices and travels downstream; such vortices produce shear stress on the sediment particles lying on the river bed and contribute to the scour process. The critical Shields stress is a function of size, shape, and material of the sediment particles. There are two current trends that study sediment transport: trend one uses computer fluid dynamics (CFD) to solve the Navier–Stokes equations; such an approach is useful for deterministic analyses and is the best option to precisely simulate the phenomenon under study, but it demands both a great amount of computer time and a high level of capabilities

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