The laboratory tests were performed to analyse the flow in curved compound channel with small relative depth. It was found that the horizontal vortices appear at the junction of a main channel and flood plains in the outside area and the secondary flows by centrifugal forces appear in a main channel.
Next, in order to simulate flow in curved compound channel, numerical computations were performed by employing one equation model as turbulent model. The result agrees well with the experiments in the middle of a main channel or flood plains, but not with the experiments at the junction of a main channel and flood plains in the outside area. To simulate the flow more accurately it was found that the effect of horizontal organized vortex must be considered. The numerical computation has revealed that flow in curved compound channel with flood plains consists of three circulating cells induced by centrifugal forces.