Research

Jeffrey Rominger

Graduate Student (Ph.D. 2013)

Current Position: Environmental Engineer
Gradient Corporation, Cambridge, Massachusetts
Email: jtr (at) alum.mit.edu


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.

Summary:
I am currently working as an environmental engineer for Gradient, a consulting firm here in Cambridge, MA. At Gradient, I'm working on a variety of projects relating to the fate and transport of chemicals in the environment. These projects span both surface water and groundwater sites, and require a variety of modeling techniques. The teams that consult on these projects come from many different specialties, including hydrology, fluid dynamics, environmental chemistry, toxicology and exposure. Similar to my work during my Ph.D., in which I studied mass flux to a flexible, moving aquatic plant, I remain interested in scientific problems that exist at the intersection of chemistry and physics.

Chen

ZB Chen

Visting Student (2011-2012)

Current Position: Ph.D. Graduate Student
Department of Hydraulic Engineering, Tsinghua University

Email: chenzb09 (at) mails.tsinghua.edu.cn

Vegetation density and patch dimension have a significant effect on the flow and vortex structure in the wake of vegetation patch, which can cause a different sediment transport behind the porous patch compared with transport in the interior vegetation zone. I am studying the effect of different submergences and densities on flow and turbulence behind the porous patch with PIV technology. Finally, I hope the results can help understand the landform evolution in streams or coastal areas.

Luhar

Mitul Luhar

Graduate Student (Ph.D. 2012)

Current Position: Postdoctoral Scholar, Aerospace
California Institute of Technology
Email: mluhar (at) cantab.net
|Web page

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.

Francois Kerger

Postdoctoral Fellow (2011-2012)

Current Position: Associate, McKinsey & Company
Luxembourg Office

Email: fkerger (at) alumni.ulg.ac.be

On top of an ecological role, vegetation in rivers and estuaries has been shown to prevent erosion of sediments and protect river banks and beds from morphological degradations. Such alterations are indeed detrimental since they may induce an increase of flood in both intensity and recurrence, as well as a decrease in water quality. The mechanism by which vegetation limits erosion is double. First, the flow low velocity in vegetation promotes the deposition of suspended load. Second, vegetation is believed to buffer the resuspension of sediments by alteration of the turbulence structure of the flow. The objective of my research is to assess the actual impact of vegetation on both the turbulent structure of the flow at the bed and its capacity to affect the bed load transport. Thanks to laser measurement of the flow velocity in a flume with different densities of emergent/submerged vegetation, I determine the bed shear stress and other turbulent parameters. These values will eventually enable me to derive formulations that predict both the threshold conditions for sediment resuspension and the bed load discharge. Such formulations are necessary to scientists and engineers for assessing the role of vegetation in existing natural ecosystem and for preparing the rehabilitation of impaired streams by using adequate plantation.

Lijun

Lijun Zong

Graduate Student (S.M. 2011)

Current Position: Junior Staff, China Development Bank
Beijing, China

Email: zonglijun (at) gmail.com

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.

Kevin

Kevin Xueyan Zhang

Graduate Student (Ph.D. 2010)

Current Position: Investment Associate
W.P. Carey Inc.

Email: xyzmit (at) gmail.com

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.

Yukie

Yukie Tanino

Graduate Student (Ph.D. 2008)

Current Position: Lecturer, University of Aberdeen
Imperial College of London, University of Aberdeen

Email: ytanio (at) abdn.ac.uk | Web page

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.

Brian

Brian White

Graduate Student (Ph.D. 2006)

Current Position: Associate Professor of Marine Sciences
University of North Carolina at Chapel Hill

Email: bwhite (at) unc.edu

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.

Lightbody

Anne Lightbody

Graduate Student (Ph.D. 2007)

Current Position: Assistant Professor of Earth Sciences
University of New Hampshire


Email: anne.lightbody (at) unh.edu

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.

Enda

Enda Murphy

Graduate Student (S.M. 2006)

Current Position: Senior Coastal Engineer
Sogreah - Artelia Group, North Vancouver, British Columbia, Canada

Email: murphye (at) alum.mit.edu

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.

Marco Ghisaberti

Graduate Student (Ph.D. 2005)

Current Position: Professor, School of Environmental Systems Engineering
University of Western Australia

Email: marco.ghisalberti (at) uwa.edu.au

Hrund Andradóttir

Graduate Student (Ph.D. 2000)

Current Position: Associate Professor, Faculty of Engineering
University of Iceland - Reykjavik

Email: hrund (at) hi.is

 

Paul Fricker

Graduate Student (Ph.D. 2000)

Current Position: Principal Consulting Engineer at The
Mathworks

Email:

Chin H. Wu

Graduate Student (Ph.D. 1999)

Current Position: Professor, College of Engineering
University of Wisconsin - Madison

Email: chinwu (at) engr.wisc.edu

home