Influence of the position and angle of a bifurcation for a secondary channel along a the bend of the main channel in the trapping efficiency of flow and sediment

MENDOZA ALEJANDRO; CABALLERO OSCAR; DOMINGUEZ RUBEN LUCAS; SZUPIANY RICARDO; BEREZOWSKY MOISES

San Francisco

Workshop; AGU Fall Meeting; 2019

AGU

Although some past studies described the flow distribution in a bifurcation (Klienhans et al., 2012), there is still little understanding for some specific cases such as bifurcations on a bend. In general, the previous studies with 2D numerical modeling have been solved for bifurcations with straight channels (Dutta et al., 2018). This research intends to carry out an approximation of the effects produced by the location and bifurcation angle with respect to a bend evaluating the trapped efficiency of flow and sediment of the secondary channel and the associated morphological evolution.The conditions considered for the analysis of the bifurcation is the case of a secondary channel originated by the splitting of the main channel; the secondary channel re-joins downstream to the main channel. Nine study cases were defined, varying the position of origin of the secondary channel with respect to the apex of the main channel (upstream, in, and downstream the apex) the other parameter varied was the bifurcation angle with respect to the centreline of the main channel (10º and 0º). For the 2D simulations, it is considered bedload and suspended sediment transport.To analyze the effect of the position and angle of the bicurcation only, the models were created considering that, 1) all the secondary channels have the same length, 2) the secondary channels reconnect downstream to the main channel in the same location and angle, 3) the main channel was modeled until it reached bed equilibrium, before connecting the secondary channel, 4) all the secondary channels have the same width to depth ratio and the initial condition was flat bed (no point bars nor pools).Results of the modelling show that both, location and angle bifurcation have a significant impact on the flow captured by the secondary channel. First, the simulations carried out show that the position of the bifurcation located upstream the apex of the main channel captures the most flow, followed by the bifurcation located in the apex; the bifurcation that captures less flow is the one located downstream the apex of the main channel. With respect to the angle, the result is expected, the more the secondary channel is aligned with the flow in the main channel, the more flow is captured. Another effect observed is that the less flow is captured, the more accretion the secondary channel develops.