I investigated the effect of rigid, emergent vegetation on lateral mixing, focusing on slower flows (stem Reynolds numbers of 200 or less) through dense vegetation. In a laboratory flume, fluorescent dye is released within a model canopy and the lateral concentration profile is measured at different distances downstream. The lateral diffusivity is then calculated from these profiles and compared with theoretical predictions.
My second project examined the hydrodynamic effects of rigid aquatic vegetation on convective currents, which are flows driven by spatial gradients in density. I developed a predictive model for the horizontal velocity and the vertical structure of gravity currents.
I am studying the exchange flow in a water body driven by spatial heterogeneity of water temperature. The presence of emergent or submerged vegetation may shelter the water and reduce the incident solar radiation. Spatial temperature gradient may arise from the difference in energy absorption, and these gradient drive lateral exchange flows. In addition, the vegetation provides significant drag that may reduce the magnitude of resulting exchange flows. The objective of the project is, by means of experiments and modeling, to evaluate the impacts of vegetation on the thermally-driven exchange flows.
I study the flow-induced reconfiguration of flexible aquatic vegetation through a combination of theoretical analysis and laboratory experiments. Many species of aquatic vegetation are flexible: they are pushed over into streamlined postures by currents, and they move passively with the flow for parts of a wave cycle. In addition to limiting the drag generated by the vegetation (advantageous in high flow environments!), this passive reconfiguration also influences light availability and nutrient uptake. By generating drag and reducing near-bed flow, aquatic vegetation limits erosion and provides shelter for fauna. By producing oxygen and taking up excess nutrients from the water, aquatic vegetation can prevent dangerous eutrophication and anoxia. As a result, an improved knowledge of vegetation reconfiguration can help coastal engineers quantify the ability of aquatic vegetation to provide habitat and prevent erosion, and help ecologists understand how flow affects the health of aquatic vegetation.
I am currently studying the interplay between the shape of flexible aquatic plants, the dynamic motion of these plants in ocean currents, and how plant shape and plant motion combine to affect nutrient acquisition and uptake rates in aquatic environments. In other words: Why do aquatic plants have different shapes in different environments? What benefits do these changes in shape confer on the plants? I am working with various species of kelp, a macroalgae, which exhibit clear morphological differences based on the intensity of the flow environments in which they live. These morphological differences suggest that dynamic forces and nutrient uptake can exert strong feedbacks on the growth and viability of kelp. Using a combination of laboratory experiments and studies of flexible body dynamics, I am working to unravel some of the links between the shape of aquatic plants and their physical environment. Ultimately, I hope that the results of this project will provide insight in the fields of fluid/solid interactions and plant physiology, and will help build understanding of how vegetation adapts to and thrives in dynamic physical environments.
Current Position: Assistant Professor of Marine Sciences
University of North Carolina at Chapel Hill
I worked on flow in channels partially filled with vegetation, typical of those in river-floodplain systems, mangroves, and salt marshes. These are interesting because, due to the drag discontinuity between the vegetation and the main channel, a shear layer develops across the vegetation interface, giving rise to an instability that forms coherent vortices. The coherent structures induce strong, periodic fluctuations in the velocity, and dominate momentum and scalar fluxes across the interface. In natural systems, these structures likely contribute to significant transport of biological and chemical material between stands of vegetation and the main channel.
Current Position: Assistant Professor of Earth Sciences
I explored the effect of transverse deep zones on the hydraulic performance of constructed wetlands that contain short-circuiting channels. I used laboratory physical models to study the effect of short-circuiting channels in wetlands and the ability of transverse deep zones to correct for these inefficiencies. Techniques include particle image velocimetry (PIV) to study flow and laser-induced fluorescence (LIF) to study transport. Concurrent field work tests whether these laboratory models replicate a real-world constructed wetland. The eventual goal is to produce design criteria that could be used by designers of constructed wetlands.
I investigated the effects of vegetation on mass transport in aquatic systems. This is a subject that is highly relevant to water quality control, channel management, wetland design, and predicting the effects of land use change. My work involves constructing tracer studies in a laboratory flume to determine dispersion coefficients for a wide range of flow regimes. This will be helpful in developing a predictive model for longitudinal dispersion in vegetated channels. The transition from deeply submerged to emergent vegetation is of particular interest, since this is a common environmental condition about which little is known. I am also working on a numerical, random walk particle-tracking model, which will give insight into mixing time scales and incorporate biological/chemical effects.
I am using laboratory experiments to study the deposition of sediment in a partially vegetated shallow channel. Sediment transport influences many physical and ecological aspects of river systems, such as nutrient cycling, water quality, channel topography and habitat diversity. Vegetation alters sediment transport by baffling the flow and creating regions of sediment retention. This retention of sediment can have a positive feedback to the persistence and expansion of vegetated regions.