Hydraulics of a submerged weir and applicability in navigational channels: basic flow structures

This paper presents the basic flow structures in a river bend in a physical model with and without a submerged weir. The CCHE2D model and the CCHE3D model for free surface and turbulent flows, which have been extensively validated and verified in recent years, are combined to study the flow in the channel in both the presence and absence of a submerged weir, where the water surface elevations and velocities are measured for certain flow conditions and in certain ranges. A 2D model is used to determine the water edge and to calibrate the bed roughness for the 3D model. A 3D model, after calibration and validation with the physical model data, is used to investigate the flow structure in the channel both in the presence and absence of a submerged weir. The agreement between the measured velocities (surface elevations) and the simulated velocities is reasonably good, which indicates that the CCHE3D model is capable of investigating the flow structure of such a channel. It is found that the submerged weir has a significant effect on the flow in the channel, and that the largest influence appears in the vicinity of the weir. Secondary flows, which are key to navigational conditions, undergo a process of break up when the flow approaches the weir, and develop into single, two, and three secondary flow zones downstream of the weir and then decay from three to two secondary flow zones and finally revert to a single secondary flow zone. Copyright q 2006 John Wiley & Sons, Ltd.