Numerical investigation of tidal forcing on the stability of bifurcations

River bifurcations are ubiquitous features of both gravel-bed and sand-bed fluvial systems, including braided networks, anabranches and deltas. As such, their morphology and development shape fluvial plains and deltas, dictating flood-prone areas as well as land loss and land gain. In this regard, bifurcations worldwide are often found unstable to any perturbation of their current state, leading to highly asymmetric discharge partitions between the branches or ultimately to the complete closure of one of them. However, in tide‐influenced deltas, it has been observed that bifurcations tend to exhibit more stable branches keeping all channels active. Therefore, although the morphodynamic equilibrium of bifurcations is strongly affected by the characteristics of the upstream channel, only lately some effort has been put into studying the action exerted by external forcings in the downstream channels. Ragno et al. (2020), inserting small-amplitude tides in the analytical model of Bolla Pittaluga et al. (2015) of river bifurcations, managed to prove that even small-amplitude tides have a stabilizing effect. In this regard, we aim at extending their analysis to the case of finite amplitude tidal forcing through a series of numerical investigations. Factors such as the length of the downstream channels or different tidal ranges are studied in order to define their influence on the evolution of bifurcations. Results show that present analytical theories are able to reproduce fairly well the increase of stability in small amplitude tidal systems, while they tend to overestimate the stability of bifurcations in higher tidal range ones. Numerical simulations show that, even when a branch gets dry during low tide due to the step formed at the bifurcation node, it might still receive river flow in high tides keeping the typical estuarine environment alive. However, increasing the tidal range to finite amplitudes, estuarine bifurcations are found to be less stable than their pure fluvial counterparts.