Vegetation-Induced Drag: An Experimental Study

Open-channel flow models through vegetative canopies require a quantitative measure of the ability of plants to absorb momentum by form drag, which is commonly characterized in terms of a drag coefficient. The present work investigates experimentally the flow structure and drag coefficients in an open channel with both rigid and flexible simulated vegetation under uniform flow conditions. Acoustic Doppler velocimetry is employed to measure three-dimensional velocity components in and above the cylinder canopy. Local values of the drag coefficient are determined from a horizontal momentum balance, which allows for the first measurements of the vertical variation of the vegetation-induced drag coefficient in open-channel flow.