Abstract
River bifurcations are prevalent features in both gravel-bed and
sand-bed fluvial systems, including braiding networks, anabranches and
deltas. Therefore, gaining insight into their morphological evolution is
important to understand the impact they have on the adjoining
environment. While previous investigations have primarily focused on the
influence on bifurcation morphodynamics by upstream channels, recent
research has highlighted the importance of downstream controls, like
branches length or tidal forcing. In particular, in the case of rivers,
current linear stability analyses for a simple bifurcation are unable to
capture the stabilizing effect of branches length unless a confluence is
added downstream.
In this work, we introduce a novel theoretical model that effectively
accounts for the effects of downstream branch length in a single
bifurcation. To substantiate our findings, a series of fully 2D
numerical simulations are carried out to test different branches lengths
and other potential sources of asymmetries at the node, such as
different widths of the downstream channels. Results from linear
stability analysis show that bifurcation stability increases as the
branches length decreases. These results are confirmed by the numerical
simulations, which also show that, as the branch length tends to vanish,
bifurcations are invariably stable. Finally, our results interestingly
show that, while in general, when a source of asymmetry is present at
the node, the hydraulically favoured branch dominates, there are
scenarios in which the less-favoured side becomes dominant.