Drag, turbulence, and diffusion in flow through emergent vegetation

Aquatic plants convert mean kinetic energy into turbulent kinetic energy at the scale of the plant stems and branches. This energy transfer, linked to wake generation, affects vegetative drag and turbulence intensity. Drawing on this physical link, a model is developed to describe the drag, turbulen ce and diffusion for flow through emergent vegetation which for the first t ime captures the relevant underlying physics, and covers the natural range of vegetation density and stem Reynolds' numbers. The model is supported by laboratory and field observations. In addition, this work extends the cyli nder-based model for vegetative resistance by including the dependence of t he drag coefficient, C-D, on the stem population density, and introduces th e importance of mechanical diffusion in vegetated flows.