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Stream deflectors are in-stream hydraulic structures that limit the flow channel width, thereby accelerating the flow through the constricted section. Single-wing and double-wing log deflectors are the two most commonly used types of in-stream eco-friendly structures. The purpose of this paper is to investigate the scour phenomena downstream of log deflectors in straight horizontal channels. The main goal is to obtain design equations to predict the main scour parameters and describe the scour morphology. All the experiments have been carried out in a horizontal channel and in clear water conditions. Log deflectors with different heights and angles were tested. Different hydraulic conditions including densimetric Froude numbers, water head drops, and tailwater values were studied. Results show that the tailwater depth and deflector angle are important variables to determine the scour parameters. Dimensional analysis leads to design equations to estimate the maximum scour depth, maximum length of the scour, and maximum height and length of the dune. Two types of scour morphology downstream of log deflectors have been defined.

Low-environment impact structures have the advantage to conjugate both hydraulic functioning and environmental care. In particular, these structure typologies are widely used for river restoration both to control sediment transport and to dissipate flow energy. In the present paper, rock grade control structures, stepped gabion weirs, block ramps, and cross-vane weirs are analyzed and compared. Both similitudes and differences in terms of scour characteristics and dissipative efficiency are highlighted. The comparison shows that block ramps are the most efficient structures among those tested. Useful practical relationships are proposed in order to estimate both scour characteristics downstream of each structures and energy dissipation.