State Key Laboratory of Hydraulics and Mountain River Engineering
Sichuan University, Chengdu, China
Email: hzh.scu (at) q.com
I study the flow and deposition around a rigid, submerged vegetation patch with different submergence depth. Three-dimensional flow structure will be present for submerged vegetation, since shear layers will be formed in the both vertical and horizontal direction which is different from two=dimensional flow adjustment for emergent vegetation. The goal is to connect the enhanced and reduced deposition regions to the flow turbulent and mean velocities, so that we can explain the deposition in different submerged conditions. These observations can also describe the morphological feedbacks between flows, deposition with submerged patches.
Graduate Student (Ph.D. 2016)
Current Position: Research Affiliate at Massachusetts Institute of Technology and
Lecturer, Boston College, Department of Earth and Environmental Sciences
Email: efinn (at) mit.edu
The feedbacks between plants, flow, and particle fate shape the size, shape, and resilence of vegetated regions, which provide key ecosystem services to the landscapes in which they reside.
Vegetation acts as an ecosystem engineer by creating distinct regions of flow diversion, turbulent mixing, and quiescent flow, dependent upon canopy physical parameters. I investigate particle fate and transport in emergent and submerged vegetated canopies through laboratory experiments and numerical modeling, connecting transport trends to the physical parameters governing the canopy mediated flow profile, as well as the particle size and density.
Postdoctoral Associate (2015-2016)
Current Positions: Postdoctoral Associate, IH Cantabria, University of Cantabria
and Research Affiliate at Massachusetts Institute of Technology
Email: mazame (at) unican.es and mazame (at) mit.edu
Numerical and experimental modeling of coastal protection provided by vegetation:
- Experimental study of waves and currents interaction with real vegetation.
- Advanced RANS three dimensional modeling and experimental analysis of waves interaction with rigid vegetation.
- New formulation for vegetation induced wave damping under waves and current condidtions.
- Wave interaction with vegetation patches.
Visiting Graduate Student (2015)
The Department of Engineering Mechanics
Tsinghua University, Beijing, China
Vegetation is known to influence its surrounding terrestrial and aquatic environments, yet the influences have not been well understood. During my postgraduate study, I mainly focus on analyzing the interaction between vegetation and environment in terms of numerical simulation. Specifically, I am performing Large Eddy Simulations (LES) of turbulent flow over model plant canopies, with the aim of visualizing the underlying fundamental processes, such as turbulent transfer and mass transport. Through this kind of research, I intend to unearth the physical mechanisms determining how momentum and scalar are transported in regions with vegetation, thus advancing our knowledge of the vegetation-enviroment interaction.
Ying "Helen" Shi
Visiting Graduate Student (2014-2015)
The Department of Hydraulic Engineering
Tsinghua University, Beijing, China
Vegetation patches have a significant impact on bio-ecological and geomorphic processes through momentum and mass exchange that occurs between the vegetation patch and surrounding environment. My current research is focused on how suspended sediment is deposited around a vegetation patch. Using an artificial rigid canopy and changing the flow conditions, I will examine the sediment distribution around the canopy. I will also explore a predictive model for the behavior of different particles under given flow conditions.
Visiting Graduate Student (2014-2015)
State Key Laboratory of Hydraulics and Mountain River Engineering
Sichuan University, Chengdu, China Email: liuchaoscu [at] vip.qq.com
The spatial distributions of velocity and deposition in the open channel near one or two vegetation patches have been extensively investigated in the past decade. These studies suggest that the sediment deposition can be related to the local velocity and turbulence kinetic energy. I considered a broader range of channel velocity, and specifically including conditions in which stem turbulence disappears within the patch. This is different from previous studies with a higher velocity. Meanwhile, people are interested in the spatial distribution of sediment deposition within and around the patch when the water moves quite slowly. I explored the change in the pattern of sediment deposition with gradually decreasing upstream velocity, and also proposed two criteria to evaluate the enhanced sediment deposition inside the patch. Currently, I am working on the further investigation for submerged vegetation patch. Behind a submerged vegetation patch, I am going to explain the complicated vortexes structure and show the corresponding deposition pattern.
Graduate Student (S.M. 2012 and Ph.D. 2015)
Current Position: Postdoctoral Fellow, Indiana University
Email: acortiz (at) iu.edu
My research is focused on the effect of vegetation patches on turbulence generation and sediment deposition. I use a laboratory flume to simulate a fluvial environment and try to understand how patches of vegetation can change overall flow dynamics and sedimentation spatially. I am interested in how different types of vegetation affect flow dynamics and sediment distribution. So if you have a flexible plant, versus a rigid plant, does it change where sediment will build up. The retention or erosion of sediment preferentially from different areas around and within a patch of vegetation can influence different aspects of the river's ecosystem and physical characteristics.
Visiting Student (2013-2014)
Current Position: Ph.D. Graduate Student
State Key Laboratory of Hydraulics and Mountain River
Engineering, Sichuan University, China
The mutual influences between biological and physical processes, called biogeomorphic feedbacks, play a key role in the landscape evolution. I am currently studying the feedback between patches of
vegetation, flow, and deposition in connection to the geomorphologic evolution of rivers and tidal flats. In particular, I am examining how neighboring patches of vegetation alter the flow field and promote deposition and growth into larger vegetation structures. The initial vegetation is modeled as a pair of adjacent patches, constructed from rigid circular cylinders. The wakes of the patches create conditions for deposition that favor patch expansion in the downstream direction. In addition, the merger of wakes from the individual patches creates regions of low velocity on the centerline between the patches that promotes eventual merger of the two original patches. We recreate the cycle of deposition-growth-flow adjustment by progressively applying artificial vegetation growth in regions of enhanced deposition. The goals are to provide new insight into the feedbacks between vegetation, flow and morphologic evolution, and to understand how vegetation adapts to and develops in different fluid environments.
Erin Grace Connor
Graduate Student (S.M. September 2014)
Email: econnor (at) alum.mit.edu
My project aims to better understand the physical mechanisms controlling nutrient acquisition by submerged aquatic vegetation. I am working to develop laboratory experiments which can help elucidate the impact of blade motion on the potential flux of nutrients to the blade surface. These experiments aim to clarify how the frequency and amplitude of flapping motions affect nutrient availability to submerged plants Experiments will also explore how uptake rates change when comparing unidirectional and oscillating flow conditions. The ultimate goal is to develop a predictive model for nutrient availability based on hydrodynamic flow conditions.
My research at MIT investigated the fluid mechanics of flow through and around patches of vegetation. I approached this first from an experimental perspective in the laboratory with my research partner Dieter Meire, who has since returned to Ghent University. We studied how finite patches of vegetation might grow into larger, cohesive structures through their own biogeomorphic feedbacks. I then expanded on this research by building a numerical model to evaluate how entire landscapes, such as wetlands, might evolve as a result of the underlying feedbacks we identified in the laboratory. The image shown at left is an example of channel formation that occurred organically in the model.
As an environmental engineer at Gradient, I work with an environmental science team to model transport processes and understand the histories of contaminated sites, such as those covered under Superfund (CERCLA). With this information, we can suggest the most productive remedial measures for contaminated sites, or determine who is responsible for leading the cleanup of a site.
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
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.
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.
Graduate Student (Ph.D. 2012)
Current Position: Assistant Professor
University of Southern California
Email: luhar (at) usc.edu|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.
Postdoctoral Fellow (2011-2012)
Current Position: Associate, McKinsey & Company
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.
Graduate Student (S.M. 2011)
Current Position: Junior Staff, China Development Bank
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 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.
Graduate Student (Ph.D. 2008)
Current Position: Lecturer, University of Aberdeen
Imperial College of London, University of Aberdeen
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 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.
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.
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.