Study On Numerical Modelling Of Compound Channel

In nature, most of river reaches tend to be compound channels and also meandering, which are composed by the main channel and adjacent floodplain. In recent years, there is an increasing concern about river flood and dike safety, because of the growing population and extensive economic activities in river floodplains. For the design and management of hydraulic engineering, it is important to understand the mechanisms of dike break and the behaviour of flows within compound channels, especially for the management of rivers and floodplains.First, an literature review has been done on the following points: the research on the mechanisms of compound channels; the roughness estimation methods and the basic theory of open channel flow; the numerical methods and models of compound channels.This study mainly presents the application of Sobek modelling system for compound channels. Sobek, which is developed by WL | Delft Hydraulics, is an integrated numerical modelling package to simulate hydrodynamics of one-dimensional river/channel network and two-dimensional overland flow. It is based on ID De Saint Venant Equation and 2D Shallow Water Equations, using an implicit scheme known as Delft scheme.Two different kinds of models have been set up in Sobek to test against the laboratory data. One is 1D2D coupling model, in which main channel is ID network and floodplain is 2D grid. Another one is fully 2D model, in which both of the main channel and floodplain are handled as 2D grids.Sensitivity analysis is undertaken on three parameters, which are the Manning roughness coefficient of the floodplain, the longitudinal slop of the flume and the sinuosity (meandering) of the main channel, in order to analyze and compare behaviours of these two models. In general, close agreement between the laboratory data and Sobek results have been obtained from both 1D2D coupling model and fully 2D model. Fully 2D model shows a better performance on overbank part, whereas 1D2D coupling model shows a better behaviour on inbank flow.