Experimental Investigation of the Characteristics of Surface Oscillations due to Passing flow Through Rigid Vegetation

By passing and strike flow with vegetation, pressure area in upstream of plant and low pressure area in its downstream is formed. The pressure difference created in this way triggers separation of the boundary layer and consequently formation of vortices downstream of vegetation. When the frequency of vortex rooted from vegetation becomes equal to the natural frequency of the channel, transverse stationary surface waves are generated. In natural channels in areas where the flow rate is on the wane, the probability of growing plants is on the rise, incontrovertibly there is a free flow beside a flow passing through the plants.
In this study, the characteristics of the surface transverse oscillations caused by vegetation, introduced as rigid barriers, were investigated under different configurations of barriers and over a range of width percentage covered by obstacles (WPO). Totally, 378 experimental tests were conducted in a rectangular channel of 9 m length and 50 cm width. The variables studied included flow discharge, flow velocity and WPO. Moreover, flow discharges were ranged from 5 to 15 liters per second. It is shown that, as long as WPO increases, transverse oscillation are formed at larger depths, which also have a larger oscillation amplitude. For a certain flow depth, increasing WPO results in growth of oscillation amplitudes. Based on dimensional analysis, regression relationships were extracted to predict the relative amplitude of transverse oscillations as a function of WPO, among other affecting parameters. Overall, the empirical equations proposed in this study were found to reproduce experimental results with acceptable accuracy.