A method for assessing the feasibility of air-bubble screens to reduce morphological gradients in open-channel bends

Within the fluvial network, confluences are particular areas characterized by great ecological value where flow dynamics and bed morphology are much influenced by local patterns. The aim of this article is to describe the influence of the convergence angle on the morphology and hydrodynamics at river channel confluences, where the tributary bed level is higher than the main channel bed (discordant bed). For that purpose, experiments were carried out in a laboratory flume running three discharge ratio scenarios for two different convergence angles (70 and 90 degrees). The tests were run until equilibrium was reached, i.e. when the outgoing solid discharge was equal or larger than 90% of the incoming. Once the bed topography remained stable, bed and water level surfaces were measured. As a result of these tests, and based on the performed measurements, the convergence angle is identified as an important parameter that influences the main-channel bed morphology features and the water level by modifying the shape and position of the main morphological and flow features. Also, the influence of the discharge ratio (Qr = Qt / Qm) on these modifications is observed and evaluated.