River bifurcations are key nodes within braided river systems
controlling the flow and sediment partitioning and therefore the
dynamics of the river braiding process. Recent research has shown that
certain geometrical configurations induce instabilities that lead to
downstream mid-channel bar formation and the formation of bifurcations.
However, we currently have a poor understanding of the flow division
process within bifurcations and the flow dynamics in the downstream
bifurcates, both of which are needed to understand bifurcation
stability. This paper presents results of a numerical sensitivity
experiment undertaken using computational fluid dynamics (CFD) with the
purpose of understanding the flow dynamics of a series of idealized
bifurcations. A geometric sensitivity analysis is undertaken for a range
of channel slopes (0.005 to 0.03), bifurcation angles (22 degrees to 42
degrees) and a restricted set of inflow conditions based upon simulating
flow through meander bends with different curvature on the flow field
dynamics through the bifurcation. The results demonstrate that the
overall slope of the bifurcation affects the velocity of flow through
the bifurcation and when slope asymmetry is introduced, the flow
structures in the bifurcation are modified. In terms of bifurcation
evolution the most important observation appears to be that once slope
asymmetry is greater than 0.2 the flow within the steep bifurcate shows
potential instability and the potential for alternate channel bar
formation. Bifurcation angle also defines the flow structures within the
bifurcation with an increase in bifurcation angle increasing the flow
velocity down both bifurcates. However, redistributive effects of
secondary circulation caused by upstream curvature can very easily
counter the effects of local bifurcation characteristics. Copyright (C)
2011 John Wiley & Sons, Ltd.