WAVE-INDUCED FORCE ON FLEXIBLE MARSH PLANTS

Salt marshes are common features in coastal regions and forming eco-rich wetlands. These wetlands provide ecosystem services, tourism and fishery benefits, as well as coast protection. Salt marshes can dissipate wave energy, which enhances coastal stability and protects the shoreline from storms and small tsunami waves. Previous wave damping predicting methods are usually oversimplified by modeling plants as rigid cylinders. Further, these studies strongly depend on the adjustment of empirical drag coefficient, while a knowledge gap exists between the mechanism of flexible plant-wave interaction. A marsh plant usually consists of multiple flexible leaves and a less flexible central stem, both the geometric and flexibility of the leaves and the stem affect the drag on the full plant. Under waves, the leaves and the stem reconfigure to different degrees at different speeds. The dynamic response of plant elements reduces the relative velocity between the wave and the plant. Further, the leaves and the stem interact with one another, making the characteristics of wave-induced plant force highly complicated. Build on the force scaling law for a simple plant element, such as a flat leaf or a cylindrical stem, we proposed a simple equation to predict the drag on plants with both leaves and stem. The force on the full plant is the sum of the force on the leaves and the force on the stem. The force on a representative leaf and the stem were estimated by the force scaling law. The force due to all the leaves was estimated by the force on the representative leaf using a sheltering coefficient, which accounts for the drag reduction in the leaves due to the interaction between the leaves and the stem. The model predicted maximum drag and the drag force over the wave period agreed well with the experiment measured drag force on an individual leaf, an individual stem, and model and live plants with both leaves and stem.