Field Study on Wood Accumulation at a Bridge Pier

Andris Wyss,Isabella Schalko,Volker Weitbrecht

doi:10.3390/w13182475

Abstract

Transported large wood (LW) in rivers may block at river infrastructures such as bridge piers and pose an additional flood hazard. An improved process understanding of LW accumulations at bridge piers is essential for a flood risk assessment. Therefore, we conducted a field study at the River Glatt in Zurich (Switzerland) to analyze the LW accumulation process of single logs at a circular bridge pier and to evaluate the results of previous flume experiments with respect to potential scale effects. The field test demonstrated that the LW accumulation process can be described by an impact, rotation, and separation phase. The LW accumulation was described by combining two simplified equilibria of acting forces and moments, which are mainly a function of the pier diameter, pier roughness, and flow properties. We applied the resulting analytic criterion to the field data and demonstrated that the criterion can explain the behavior of 82% of the logs. In general, the field observations confirmed previous results on the LW accumulation probability in the laboratory, which supports the applicability of laboratory studies to investigate LW–structure interactions.

Highlights

IntroductionThe amount of transported large wood (LW) can exceed the transport capacity of a river section and pose an additional flood hazard [1,3,4]
This paper aims to improve the process understanding of the large wood (LW) accumulation process at bridge piers, extend the introduced force balance [20] to describe why logs accumulate at bridge piers, and discuss potential model scale limitations
The field test demonstrated that the LW accumulation process can be described by three phases: the impact phase, rotation phase, and the separation phase

Summary

Introduction

The amount of transported LW can exceed the transport capacity of a river section and pose an additional flood hazard [1,3,4]. LW may block at river infrastructures such as bridge piers (Figure 1), leading to increased water levels and potential flooding, or structural risks. The analysis of LW transport and accumulation processes, including the accumulation probability of LW at bridge piers, is key to improve the flood hazard assessment. The LW accumulation process has been investigated for different bridge types ranging from bridge decks to individual bridge piers [5,6,7,8,9,10,11,12,13,14,15,16,17,18]

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