Biomechanical Properties of Aquatic Plants: Implications for Hydraulic Engineering and Aquatic Ecology

Aquatic vegetation in rivers often modifies hydraulic resistance and can enhance seasonally occurring flooding. To which extent a plant constitutes an obstacle in the flow is strongly influenced by its biomechanical traits which determine the ability of plants to reconfigure in the flow, i.e. to adopt a shape that minimizes drag forces and hence to smooth the flow dynamics in and around submerged macrophyte patches. The objective of this study is thus to advance the understanding of hydraulic resistance due to vegetation by studying biomechanical characteristics of aquatic plants. The biomechanical properties of stems of four submerged river macrophyte species, typical for northeastern Scotland, have been studied in detail using cyclic loading/unloading tests. The test techniques have been adjusted to account for specific properties of the plant materials. The data analysis involved the assessment of statistics of material properties with a focus on between-species variations. We found that plant species in habitats with high water velocities have flexible stems with little plastic deformation and a high breaking force and breaking stress. Plant species growing in habitats with less fierce flow possess less flexible stems with lower breaking stresses and breaking forces and show a higher plastic deformation. The results of this study should help in the identification of relevant roughness parameters due to vegetation as well as in defining critical flow conditions for the eradication of invasive, exotic plant species and the conservation of rare, protected plant species.