ABSTRACT
In large rivers, alternate expansion and contraction of channels are very common. It caused due to presence of hard points of geological formations or human activities. The expansion and contraction of the channel modifies the flow hydraulics and thus affect the river morphology. The flow velocity at the contracted section increases and the increased velocity at the expanded sections erode the side wall material and hence it increases the width of channel at the downstream. The expansion causes velocity variations along the channel transect. This is adjusted by increase in river width by action of bank erosion. At the contracted sections, velocity increases which can in turn increase the shear stress at the bed level, due to which the material at the bed level adjoining the hard points gets eroded. In the present study, an experiment was conducted by forming the alternate expansion and contraction of the channel. Three-dimensional flow behaviour was measured with the ADV at various transect along the flow. Analysis of the flow structure indicates the initiation of sediment deposition which was verified from the morphological changes in the section.
