Topographic forcing of flow partition and flow structures at river bifurcations
Version of Record online: 14 FEB 2012
Copyright © 2012 John Wiley & Sons, Ltd.
Earth Surface Processes and Landforms
Volume 37, Issue 6, pages 666–679, May 2012
How to Cite
Miori, S., Hardy, R. J. and Lane, S. N. (2012), Topographic forcing of flow partition and flow structures at river bifurcations. Earth Surf. Process. Landforms, 37: 666–679. doi: 10.1002/esp.3204
- Issue online: 16 APR 2012
- Version of Record online: 14 FEB 2012
- Accepted manuscript online: 9 JAN 2012 05:21PM EST
- Manuscript Accepted: 20 DEC 2011
- Manuscript Revised: 15 DEC 2011
- Manuscript Received: 1 MAR 2011
- Reynolds-averaged Navier–Stokes model;
This paper presents the predicted flow dynamics from the application of a Reynolds-averaged Navier–Stokes 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 © 2012 John Wiley & Sons, Ltd.