INFLUENCE OF THE POSITION AND ANGLE IN THE FLOW AND SEDIMENT TRAPPING EFFICIENCY IN BIFURCATIONS ALONG BENDS

CHISTIAN CABALLERO; LUCAS DOMINGUEZ RUBEN; ALEJANDRO MENDOZA; JORGE ABAD; MOISES BEREZOWSKY

Concordia

Congreso; MECOM 2023; 2023

AMCA

The permanence of secondary channels in natural bifurcations depends on various factors,including geo morphological, geotechnical, geometric, and hydr o sedimento logy conditions,particularly their capacity to capture both flow and sediment. In this regard, at bifurca tion s, secondarychannels can either capture the entire flow, be abandoned, or reach st eady flow and sedimentdistribution with respect to the main channel. While there are studies that analyze partition dynamics,very few have been conducted at bifurcations o n bends reaches (with complex flow structure ), whichare the most common in large allu vial rivers . To analyze the impact of the position and angle ofbifurcation around a bend, we conducted a series of two dimensional fluvial morphological numericalsimula ti ons under different geometric scenarios. We carr ied out nine cases, modifying the p osition ofthe secondary channel outlet relative to the main channel (upstream, at the apex, and downstream), andfor each of these, we varied the angle (0, ±10°). The sim ul ations represent two dimensionalhydrodynamics, sediment transport (bed and suspend ed sediment), and morphological changes, usingthe TELEMAC 2D model coupled with the Sisyphe module. The results indicate that the position ofthe bifurcation along the be nd influences sediment and flow capture (and, consequ ently, thepermanence of the cha nnels). Firstly, it is worth noting that bifurcations located upstream of the apexachieve a higher flow capture (between 7 25% more than the other positions, at the apex an ddownstream), resulting in secondary channels with higher erosion rates. Simultane ously, the mainchannel experiences a loss in total transport capacity, leading to significant deposition processes.Secondary channels positioned downstream of the apex a re more efficient at capturing sediment,leading to a rapid equilibrium over time and a lower capture of flow by the secondary channel (2040% of the main channel). Similar results are observed for bifurcations positioned at the apex. Theangle of the seco nd ary channel´s exit does not seem to significantly a ffect the overall behavior, withpercentage deviations of 2 5% in each of the positions. Regarding the free surface, it undergoesmodulation during the process of adapting flow and sediment distribution. A n increase in watersurface elevation upstream of the bifurcation enhances the grad ient energy in the secondary channel,intensifying its capacity to capture sediment transport. Lastly, it is important to note that thedevelopment of maximum velocities a lo ng the bend could affect flow partitioning, as the higher flowinertia on the main channel reduces the capture capacity of the secondary channel.