Bridge pier flow field in the presence of debris accumulation

The accumulation of debris and drifts around a bridge pier can substantially modify the local scour pattern. These local accumulations influence the hydraulic structure, which results in a new scour configuration. As a result, the scour hole dimensions generally increase as debris accumulation increases. Moreover, the scour process is also affected by the roughness of the accumulation. This paper investigates the time-averaged flow field of debris accumulation at a cylindrical bridge pier and analyses the influence of debris roughness on the flow field. Velocity fields were examined in the presence of different rough debris accumulations with a constant frontal area of 5% of the total flow area. The data confirm the effect of debris accumulation on the flow field compared with pilot tests. The flow field generally resulted in larger flow velocities and turbulence near the pier and in the pier wake. Finally, the data show that the roughness of debris accumulation affects the development of the boundary layer underneath the debris, the downflow intensity and the maximum observed velocities.