A Methodology to Measure Flow Fields at Bridge Piers in the Presence of Large Wood Debris Accumulation Using Acoustic Doppler Velocimeters

Abstract

Bridge failure due to scour in flooding conditions has been at the center of attention of hydraulic engineers for decades. Large wood debris accumulation on bridge piers has been found as one of the main causes for bridge collapse. The combined action of enhanced scouring at the base of the pier and increased hydrodynamic load is viewed as the main force driving the enhanced failure probability. It is therefore fundamental to understand the distribution of the flow field around the accumulation and in the proximity of the pier, in order to be able to understand the potential acceleration and turbulence enhancement that could help understand what drives the failure and reduces its probability. However, this particular configuration poses physical constraints to flow measurements, as the accumulated mass of logs hinders a direct access to instrumentation directly immersed in water. This paper proposed a new methodology to measure the flow fields in the presence of debris accumulation using an acoustic Doppler velocimeter (ADV). The methodology consists in applying a matrix of rotation on the instantaneous velocity measured in the three dimensions to access locations underneath the debris that could not be accessed using the standard rotation of the debris. The methodology shows the potential to provide accurate measurements in the proximity of the debris and the groove and is able to maintain the statistics of the flow fields in terms of both average velocity and turbulence intensity.