An experimental study of the incipient bed shear stress partition in mobile bed channels filled with emergent rigid vegetation

This paper investigates the bed shear stress based on the condition of the incipient motion of sediment in a uniform-flow flume covered with emergent rigid vegetation, which is represented by arrays of circular cylinders arranged in a regular pattern. A total of 148 tests are performed to observe the influence of the vegetation density, bed slope, flow depth and sediment size on the bed shear stress. The tests reveal that when the sediment is in incipient motion, the resistances acting on the flow passing the rigid vegetation contain the vegetation resistance and the bed shear stress. This shear stress could be divided into two parts: the grain shear stress and the shear stress caused by sand dunes, which are the deformed bedform with the sediment incipient motion. An empirical relationship between the shear stress of the sand dune and vegetation density, the Froude number, the apparent vegetation layer velocity is developed.