Modeling the interaction between wave hydrodynamics and flexible aquatic vegetation

Aquatic vegetation, found in coastal waters and inter tidal areas, has important features for hydraulic engineering solutions, including sedimentation and stabilization of the bed. The increasing demand to predict wave hydrodynamics with aquatic vegetation asks for insight in the mechanisms and improved model methods. Striving to a more fundamental approach of the interaction between wave hydrodynamics and flexible vegetation by determination and description of phenomena and processes is the main objective of this research. The interaction is divided into two one-way couplings: the wave hydrodynamics affected by a canopy of rigid vegetation and the wave-induced motion of single stem vegetation. The interaction is studied with two unique wave flume experiments and with the development of the 1DV-Dynveg model for simulating the motion of flexible vegetation in periodic wave conditions. Measurements and model results of wave hydrodynamics in and over rigid vegetation reveal reduced in-canopy velocities with phase leads compared to the surface elevation. A mixing layer is generated, moving in and out the canopy, with strong velocity gradients and vertical motion of horizontal momentum. The height and motion of the mixing layer varies with canopy characteristics and wave conditions. Period averaged streaming in the mixing layer is observed in the wave propagation direction with a redistribution of the Stokes' drift. The wave-induced motion and the base forces on and of single flexible stems are measured and modeled. Forces on rigid cylinders are in general proportional to the squared flow velocities. Due to lower relative velocities between the stem and the flow, lower base forces are observed with flexible vegetation. Streamlined positions are observed with larger orbital velocities, reducing the base forces, even with relative stiff stems.Environmental Fluid DynamicsHydraulic EngineeringCivil Engineering and Geoscience