This paper presents the results of an experimental study on the interaction between the flow in a “wide” main channel and the flood-plain. This interaction region has been shown to resemble a shear layer with some control exercised by the bed shear stress. The length scales of this interaction region as well as the reduction and increase of bed shear stress in the main channel and flood plain respectively, in dimensionless forms, have been correlated with D/d, the ratio of the flow depths in the main channel and the flood-plain.