Experimental study on flow mechanisms in a sine-shaped meandering compound channel

Hydrodynamic processes in compound channels are closely related to the cross-sectional geometry of the river. The cross-sectional shape of natural meandering rivers is always irregular, with a curved main channel (MC) and one or two floodplains (FPs), and most are confined within levees. The geometric shape of the cross-section of such rivers changes greatly in a flood, which influences the exchange of momentum and energy between the MC and FPs. Many previous studies have focused on flow mechanisms in compound meandering channels of relatively regular and simple cross-section, which is not representative of natural rivers. An experimental study of a sine-shaped meandering compound channel of irregular shape and with levees was thus conducted. Using detailed experimental data, the development of streamwise flow, secondary flow and turbulent shear stresses over the cross-sections were analysed. Special emphasis was placed on the momentum exchange between the MC and FPs. The results showed that flow transport in the MC plays a leading role and the momentum exchange between the MC and FPs is more intensive for a high water level. The formation, development and decay of secondary flow in compound meandering rivers are closely related to the momentum exchange between the FPs and the MC. Finally, transverse flow plays a dominant role in the process of momentum exchange and the effects of turbulence are negligibly small.