Morphodynamic differences induced by different confluence angles in widen confluences

River widening is commonly used as a solution for the rehabilitation of rivers with the main purposes of allowing the river to adjust to its natural dynamics and to improve riparian and instream habitat for flora and fauna, by increasing the heterogeneity in substrate, flow and morphology. Local widening may also be used for confluences rehabilitation as, for many of them, the heterogeneity and fragmentation of the river system were severely affected by previous human interventions. Local tributary widening amplifies the morphodynamic processes, enhancing the diversity in sediment substrate, flow velocities and flow depths. In addition, widening should neither affect aspects such as water level in the tributary nor in the main channel, which is an important consideration for flood safety. The aim of this paper is to analyze the differences in terms of bed morphology and flow dynamics induced by different confluence angles in widen channel confluences. effects of discordant bed on the flow dynamics in channel confluences. Although the flow dynamic in confluences is well known, only few laboratory experiments were carried out under mobile bed conditions (Mosley, 1976; Best, 1988; Boyer et al., 2006; Best & Rhoads, 2008; Leite Ribeiro et al., 2012a; b), among which only Boyer et al. (2006) and Leite Ribeiro et al. (2012a; b) were based on discordant-bed confluences. Leite Ribeiro et al. (2012b) studied the efficacy of local tributary widening as potential solution for confluence rehabilitation focused on discordant bed confluences, in which the tributary bed level differs from the main-channel bed level at the tributary mouth. This study was based on experiments under mobile bed conditions, carried out in a laboratory confluence where the tributary and main channel joined with a 90o angle, and where sediments were only supplied in the tributary. Leite Ribeiro et al. (2012) concluded that local tributary widening can enhance heterogeneity in sediment substrate, flow velocities and flow depths, improving the local habitat and the connectivity of the