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This paper presents the results of a laboratory study on flow past cylindrical piers placed on smooth, rough, and mobile beds. Experimental results are presented on the flow in the plane of symmetry, including the frontal downflow and the effects of bed roughness and the scour hole on it. The Clauser-type defect scheme describes the velocity profiles better than the log-law and defect law. Frontal downflows as large as 95% of the approach flow were observed. Experimental results are also presented on the deflected flow and bed shear stress field. Bed roughness increased the magnitude of bed shear stress and the area over which the shear amplification was felt and also resisted the skewing of the flow near the bed, thus leading to smaller yaw angles of the bed shear vectors.
Ahmed et al. (1998) studied this question.