Study of the Impact of Vegetation Direction and Slope on Drag Coefficient

In order to understand the influence of vegetation on resistance to overland flow, the relationship between drag coefficient and flow depth was modeled and studied for three types of vegetation distributed at four different slopes (0, 0.5,1.0, and 3.0%) based on three angles (30 degrees, 45 degrees, and 90 degrees) between the vegetation row direction and flow direction. An indoor fixed-bed erosion test was used for this study, and the vegetation stem was simulated by a cylinder. The results show that at the same slope and flow depth, the drag coefficient of vegetation decreases as the angle between the vegetation row direction and the flow direction increases; at the same slope and angle, the drag coefficient of the vegetation first decreases and then stabilizes as the flow depth increases. A threshold depth was found beyond which the flow depth no longer affected the drag coefficient of vegetation. The threshold depth decreased with the increase in slope; thus, the slope affects the drag coefficient of vegetation by altering threshold depth.