Flow, Turbulence, and Resistance in a Flume with Simulated Vegetation

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. An experimental study was performed to investigate the flow structure and drag coefficients in an open channel with both rigid and flexible simulated vegetation under uniform flow conditions. Acoustic Doppler velocimetry was employed to measure three-dimensional velocity components in and above a cylinder canopy. Local values of the drag coefficient were determined from a horizontal momentum balance, which allowed for the first measurements of the vertical variation of the vegetation-induced drag coefficient in open-channel flow. Results show that the drag coefficient is not constant in the vertical, as many models have assumed, but instead, varies throughout the height of the water column.