Validation of Observed Bedload Transport Pathways Using Morphodynamic Modelling

Abstract

Braiding is a mesmerizing phenomenon since flow and sediment transport interact and are able to change the morphology of a channel in a rapid and complex fashion. Conventional two-dimensional morphodynamic models estimate bedload distribution using shear stress distribution. However, it is unclear if the use of such shear stress distributions is relevant or applicable for all situations when using two-dimensional morphodynamic modelling. This thesis strives to investigate whether shear stress distributions are useful to predict bedload transport pathways. This study focuses upon prediction of bedload transport pathways using a morphodynamic model (Delft3D) of an anabranch of the Rees River (New Zealand). Observed bedload transport pathways were compared to modelled bedload transport pathways in an attempt to validate the predictive ability of the model. Results show that there is a significant correlation between predicted bedload transport pathways and the apparent bedload transport pathways derived from the field measurements. Furthermore, bedload transport predictions were in good agreement with observed data in areas where the model’s predictions of high shear stress were comparable to field observations. However, substantial bedload transport predictions in low shear stress areas were not adequately captured by the model, suggesting that the observed pathways were not due to high shear stress, but rather to other sediment supply sources.