In nature, most river reaches tend to be compound channels as well as meandering. For the management of rivers and floodplains, it is important to understand the behaviour of flows within compound channels. The stage-discharge curve is essential for risk management and flooding damage assessment. This study dealt with the application of the SOBEK modelling system for compound channels. Developed by WL / Delft Hydraulics, SOBEK is an integrated numerical modelling package used to simulate hydrodynamics of one-dimensional river/channel network and two-dimensional overland flow. It is based on the 1D De Saint Venant Equation and the 2D Shallow Water Equations, using an implicit scheme known as the Delft Scheme.
Two different kinds of models were set up in SOBEK to test against the laboratory data of the Aberdeen experiment from Database on Conveyance in River/Floodplain Systems, set up by the University of Glasgow. One is a 1D2D coupling model, in which the main channel consists of a 1D network and the floodplain of a 2D grid. Another one is a full 2D model, in which both the main channel and the floodplain are treated as 2D grids.
Sensitivity analyses were performed on three parameters: the Manning roughness coefficient of the floodplain, the longitudinal slope of the flume, and the sinuosity (meandering) of the main channel, in order to analyse and compare the behaviours of these two models. In general, close agreement between the laboratory data and the SOBEK results were obtained from both the 1D2D coupling model and the full 2D model. The Full 2D model shows a better performance on the overbank section, whereas the 1D2D coupling model shows a better behaviour on the inbank flow. Both models seem to underestimate the effects of longitudinal slope and sinuosity of the main channel.
This project was executed in cooperation with UNESCO IHE Delft (MSc study). |
