Author(s): Sanjay Giri; Satomi Yamaguchi; Mohamed Nabi; Jonathan Nelson; Yasuyuki Shimizu
Linked Author(s): Jonathan Nelson, Sanjay Giri, Yasuyuki Shimizu
Keywords: River dunes; The Waal; Numerical modelling; Vertical 2D model; 1D SOBEK model
Abstract: This The Waal branch of Rhine system is considered to be an important fairway. The flood events and extensive navigation cause significant morphological changes, which create difficulties for safe and efficient navigation particularly during low water period. Therefore, it is important to predict the bed level changes, particularly evolution of bed forms during the flood event including both the high water and low water periods. Besides this, it is also important to understand the bed form evolution process and resulting flow resistance during extreme floods in order to quantify their effect on water levels. Many attempts have been made to improve both understanding and predictive capability of bed form evolution, transition and associated resistance under varying flow conditions. The interaction among the flow-field, bed forms and sediment transport is quite complex and difficult to capture in simple models. A number of our recent studies have made some noticeable efforts to numerically replicate the dune formation and evolution processes. A morphodynamic model was been developed that successfully reproduces fluid and bed form dynamics in a coupled manner under arbitrary steady or unsteady flow condition. This study is the continuation of our previous efforts, in which we have attempted to replicate the flow and bed form evolution process under a couple of synthetic (extreme) flood scenarios in the river Waal. Within the scope of this study, at first, we have analyzed the observed data during moderate floods in the Waal. The bed level data were measured during a moderate flood event in 1997. A vertical two-dimensional morphodynamic model with a free-surface flow condition, which includes equilibrium, non-equilibrium bed load as well as suspended sediment transport modules, has been used to replicate the flow and bed form evolution processes under extreme flood conditions. The boundary condition (unit discharge and water levels) for vertical two-dimensional model was extracted from a calibrated onedimensional hydrodynamic model SOBEK, developed for the Rhine branches. A preliminary result shows that bed forms are present even during extreme flood condition. This study reveals the capability of a numerical model, which can be applied to predict real-world river dunes and drag evolution with hysteresis effects in physics based manner.
Year: 2015