Impact of foliage on the drag force of vegetation in aquatic flows

The objective of this study was to determine the contribution of a plant's foliage to the total plant's hydrodynamic drag. Experiments were conducted in a laboratory flume using samples of vegetation with different physical forms and biomechanical properties: Branches of pine (Pinus sylvestris) and ivy stipes (Glechoma hederacea). The drag force was measured directly using a strain gauge technique and determined for a series of velocities for each vegetation species with and without foliage. Experimental results revealed a distinct contribution of foliage to the total plant drag. For both plant types, this was particularly marked at lower velocities where the foliage is not streamlined and compressed and, hence, the frontal projected area of the plant is at a maximum. It was found that the flexibility of the plant's foliage and its ability to streamline with the flow may reduce the overall drag considerably. There was a distinct difference in the C(d)A(P) parameter-velocity squared relationship between the with foliage plants and nonfoliage counterparts due to the streamlining effect of the foliage with the flow and, hence, the reduction in overall drag associated with the new compressed plant form.