Flow velocity in non-uniform gravel surface: an experimental investigation

The evaluation of the kinematic characteristics of flow in gravel-bed rivers is one of the most important problems. In the present paper the stream-wise velocity profiles are inves-tigated on the basis of data collected in a straight laboratory gravel-bed flume. Two differ-ent non-uniform rough beds, respectively characterized by d84=1.1 cm and by d84=6.0 cm, have been examined. The image-based technique is used to identify the gravel-bed struc-ture and thus the local reference level for analyzing the local effect on the flow velocity profile. Results show that the vertical velocity profile tends to form an inflection point de-pending not only on the value of h/d84 ratio but also on the value of the Froude number.