THREE-DIMENSIONAL NUMERICAL MODELING OF FLOW AND SEDIMENT TRANSPORT AT AN EXPERIMENTAL-SCALE 90-DEGREE FLUVIAL DIVERSION

Bifurcations are an important feature of fluvial systems, and diversions are a subset of bifurcations where one of the channels after bifurcation continues along the same direction of the original channel. Dynamics of flow and sediment at fluvial diversions have implications for both natural and engineered fluvial systems, primarily due to their influence on the geomorphological evolution of the diversion. One of the first set of experiments on the diversion was conducted in 1926 by Bulle. The experiments put forth the phenomenon of highly non-linear distribution of near-bed sediment between the lateral and the main channel of the diversion, which is also known as the Bulle-Effect. Since 1926, there have been several experimental studies that have confirmed the phenomenon. All the experiments of Bulle that have measurements of sediment distribution were done with a rigid bed, which is different from an actual natural system. Recently Herrero (2013) repeated the 90-degree experiments of Bulle with bed of sand. The experiments confirmed the phenomenon of Bulle-Effect, and also put forward geomorphological features that may be formed due to it. On the modeling front, a recent study has been relatively successful in simulating the flow features and sediment distribution patterns observed in Bulle’s experiments using a three-dimensional finite-element based hydrodynamic model (Dutta et al., 2016). The numerical study is important because it acts as a proof of concept towards using a similar model to predict geomorphological evolution in the field. It also allows detailed study of the flow and sediment distribution patterns. The current study simulates the experiments done by Herrero (2013), in order to further explore the flow patterns and geomorphological evolution observed in the experiments.