The shear stress acting on the bed around vertical circular cylinders and artificial seaweeds installed in a wave flume with multiple rows is measured by using a shear stress sensor which is one component load cell. The sand movement and local scour around these plant models are also observed. The close agreement between the time variation of shear stress measured by the shear stress sensor and the estimated values from the theoretical values of boundary layer equation in harmonic flow with laminar flow are obtained in the case of regular wave with smooth plate. The values of shear stress on the smooth bed with vertical circular cylinders increase compare to the shear stress on the bed without vertical circular cylinders. The amplification of shear stress on the smooth bed around a vertical circular cylinders due to the vortex shedding occurring at the lee side of the cylinder is evaluated quantitatively. The sand in side of these plant models move mainly in the direction of shoreline. These phenomena may be due to the disappear of ripple on the sand bed with circular cylinders.

       The shear stress acting on the bed around vertical circular cylinders  installed in an open channel with single and multiple rows are also measured by using the shear stress sensor. The values of friction coefficient and Manning's roughness coefficient in the part of bed increase with increase of arrangement density of multiple rows of vertical circular cylinders in the open channel.