Drag, turbulence, and diffusion in flow through emergent vegetation

TLDR

Aquatic plants convert mean kinetic energy into turbulent kinetic energy at the stem and branch scale, and this energy transfer, linked to wake generation, affects vegetative drag and turbulence intensity. The study aims to develop a model describing drag, turbulence, and diffusion in flow through emergent vegetation that captures the underlying physics across vegetation density and stem Reynolds numbers. The authors extend the cylinder‑based vegetative resistance framework by incorporating drag‑coefficient dependence on stem density and mechanical diffusion, thereby covering the natural range of vegetation density and stem Reynolds numbers. Laboratory and field observations support the model’s predictions.

Abstract

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, turbulence and diffusion for flow through emergent vegetation which for the first time 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 cylinder‐based model for vegetative resistance by including the dependence of the drag coefficient, C D , on the stem population density, and introduces the importance of mechanical diffusion in vegetated flows.