How submerged plants go with the flow

Whether along rivers, lakes, wetlands, or shorelines, submerged vegetation plays a crucial role in waterfront ecosystems. Such plants can change the flow of water and trap sediments, nutrients, pollutants, and organisms, influencing flooding, erosion, habitat quality, and water quality. However, natural plant variation makes consistent experimentation difficult, and physical and numerical models often use simplistic vegetation shapes such as strips or cylinders.

Fu et al. designed a submerged plant surrogate with a thin, compliant stem and many distributed clusters of leaf-representing pellets. Through experiments and modeling, they determined the essential physical mechanisms underlying this aquatic plant shape.

“Not all submerged plants look or behave like simple blades,” said author Jiahao Fu. “We needed a simpler and more controllable way to represent this class of plants without losing the main force balance that controls their posture.”

The researchers designed a surrogate using thin rope as the filamentous stem and small balls as the leaf clusters. Then, they developed a mechanical model that balanced drag, buoyancy, and tension. Lastly, the researchers placed surrogate plants with varying pellet size, density, number, and distribution in flowing water of different speeds, recorded their motion, and compared the measurements with the model predictions.

The team found that the surrogates bent more when the water flow was stronger, when the pellets were less buoyant, and when the drag force was larger relative to the upward buoyant force.

“[This work] provides a bridge between natural plant complexity and tractable laboratory or numerical models,” said Fu.

In the future, the researchers hope to extend their surrogate-model approach to studying plant swaying, not just bending.

Source: “Representing submerged flexible vegetation with buoyancy-dominated, non-unform surrogates,” by Jiahao Fu, Guojian He, Shengli Chen, Vladimir Nikora, Subhasish Dey, and Hongwei Fang, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0344153 .