Effects of submerged sheet pile vanes on mobile river beds

Submerged vanes are low-height flow-training structures emerging from the riverbed with a suitable angle of attack to the incoming flow. These structures redirect the stream flow modifying erosion and depositional rates in the bottom and in the banks of a river as a result of the secondary currents generated by their installation. For this reason, they have a large number of applications in river hydraulics in order to control river bed morphology. Here, an experimental investigation is carried out in order to compare the efficiency of sheet-piling vanes versus thin plane ones in controlling sediment redistribution in channel bed. In particular, experimental tests were carried out within a straight water channel, in conditions of bed load motion. The morphology of the river bed both in the area close to the structure and in the far field was examined at different angles of attack of the vane to the incoming flow and different values of the submergence parameter, that is the ratio between the height of the water above the structure and the water level. The experimental results show that the shape of the vanes as well as the angle of attack affect their performance in terms of the effects on the bed morphology, especially for the greater submergence parameters. Specifically, plane and sheet-piling vanes produce a comparable remodeling of the channel bed in the downstream region but, when the attack angle increases, the thin plane vane causes deeper scour holes close to the structure. This last effect is probably due to the increasing erosive capacity of the horseshoe vortex associated to the plane vane, while the uneven surface of the sheet piling vane mitigates the erosive strength of the vortex.