A New Predictor of Turbulence Metrics for Wave-Dominated Flows through Submerged Aquatic Vegetation

Abstract:

Aquatic vegetation in coastal and estuarine environments interacts with waves to generate turbulence across stem- to canopy-scales. However, we know little about the relations between these vegetation-driven scales in wave-dominated flows. Understanding the flow and turbulence structure across canopies in wave-dominated flows may help us understand the impact of aquatic vegetation on physical and ecological processes. We investigate turbulence and hydrodynamic interactions between oscillatory flows and aquatic vegetation using 2D and 3D particle image velocimetry (PIV) techniques. 2D and 3D PIV data allow us to measure multi-component velocity fields in patches of submerged vegetation in a sediment bed. We conduct the experiments in a U-shaped oscillatory tunnel where we use rigid cylinders in a bed of crushed walnut shells. We estimate turbulence intensities, Reynolds and dispersive stresses, and flow structure with high spatial resolution over a wide range of flow and vegetation conditions. We present a new relation for near-bed turbulent kinetic energy (TKE), and mass exchange estimations at the top of the submersed plants. Our work provides a connection between turbulence and relevant time- and length-scales in the highly 3-dimensional vegetated flow when only two-dimensional or single-point measuring techniques are available. Our findings improve understanding of flow within coastal and estuarine ecosystems, allowing us to predict maximum near-bed TKE and estimate the canopy-to-stem scale transformation via vegetation drag at the top of the canopy. While coasts and estuaries face new anthropogenic stressors, our results provide an easy-to-use tool for conservation and restoration practices in wave-dominated environments.