Visualization of the Bulle-Effect at River Bifurcations

The visualization highlights the phenomenon of non-linear distribution of near-bed sediment at asymmetric river bifurcations, also known as the Bulle-Effect. The visualized results were generated on Blue Waters (at NCSA), using the open-source high-order spectral element based Navier-Stokes solver Nek5000 coupled with a Lagrangian particle tracking model developed for this study. The Bulle Effect causes sediment in the lower part of the water-column to preferentially move into the lateral-channel, even in cases where a relatively higher percentage of the total flow continues along the main-channel. This has implications for the construction of such channels for use in irrigation, navigation and delta restoration. The visualization emphasizes the difference in dynamics of sediment traveling at different depths of the channel, this helps animate the mechanism behind the Bulle-Effect succinctly. Additional flow features, such as velocity magnitude and coherent structures, have also been visualized to enhance our understanding of the interactions between the flow and sediment.