This paper presents the predicted flow dynamics from the application of
a Reynolds-averaged NavierStokes model to a series of bifurcation
geometries with morphologies measured during previous flume experiments.
The topography of the bifurcations consists of either plane or
bedform-dominated beds which may or may not possess discordance between
the two bifurcation distributaries. Numerical predictions are compared
with experimental results to assess the ability of the numerical model
to reproduce the division of flow into the bifurcation distributaries.
The hydrodynamic model predicts: (1) diverting fluxes in the upstream
channel which direct water into the distributaries; (2) super-elevation
of the free surface induced at the bifurcation edge by pressure
differences; and (3) counter-rotating secondary circulation cells which
develop upstream of the apex of the bifurcation and move into the
downstream channels, with water converging at the surface and diverging
at the bed. When bedforms are not present, weak transversal fluxes
characterize the upstream channel for almost its entire length,
associated with clearly distinguishable secondary circulation cells,
although these may be under-estimated by the turbulence model used in
the solution. In the bedform dominated case, the same hydrodynamic
conditions were not observed, with the bifurcation influence restricted
and depth scale secondary circulation cells not forming. The results
also demonstrate the dominant effect bed discordance has upon flow
division between the two distributaries. Finally, results indicate that
in bedform dominated rivers. Consequently, we suggest that sand-bed
river bifurcations are more likely to have an influence that extends
much further upstream and have a greater impact upon water distribution.
This may contribute to observed morphological differences between
sand-bedded and gravel-bedded braided river networks. Copyright (C) 2012
John Wiley & Sons, Ltd.