In compound open channel flows, the momentum transfer from the main channel to the flood plain is a strong characteristic and the contribution of the secondary flow is known to be very large. In this study, numerical simulation is conducted to understand the secondary flow effect on the lateral momentum transfer with a standard k-ε model linked artificially with a given secondary flow. This simulation reproduces the typical linear distribution of the momentum transfer term. The simulated secondary flow can decrease the bed shear stress in the main channel. In cases of large relative depth, the secondary flow explains the bed shear stress increase on the flood plain reasonably well, but an unrealistically large secondary flow is required to reproduce the experimental apparent shear stress in cases of small relative depth. Hence another mechanism, like large-scale planform vortices, is needed to explain the characteristic increase of bed shear stress on the flood plain.
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