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The Current Nepf Lab, November 2014
Gary Lei, Marissa Fryer, Judy Yang, Heidi Nepf, Elizabeth Follett,
Helen Shi, Chao Liu

Heidi Nepf
Donald and Martha Harleman Professor
Civil and Environmental Engineering


Email: hmnepf (at) mit.edu

Heidi Nepf's Civil and Environmental Engineering webpage
Professor Nepf's teaching includes Physical Limnology and Transport Processes in the Environment.


Elizabeth Follett

Graduate Student (Email: efinn (at) mit.edu
)

By forecasting the spread of fungal spores, we can reduce the amount of fungicide applied each year to crops such as corn, wheat, and soybeans. My research focuses on developing an understanding of the processes governing spore escape from a crop canopy, so that we can refine existing estimates of the probability of spore escape. Using a rigid model crop canopy, I study theimpact of canopy scale vortices on particle transport using a combination of flow visualization techniques and measurements of deposition following an experimental particle release. I have also developed a simple random walk particle tracking model to explore particle escape across a wide range of canopy densities and ratios of spore settling velocity to canopy turbulence.



Alejandra Ortiz
Graduate Student (Email: aleja.ortiz (at) gmail.com)

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.

 

Qingjun "Judy" Yang
Graduate Student (Email: qjyang (at) mit.edu)

My current research is focused on the sediment transport inside a vegetation patch. Vegetation is a basic component of most natural water environments and has been widely used in river restoration. Yet few practical models exist to predict the incipient motion and rate of sediment transport in a canopy. Using a LDV, a high-speed camera and a sediment-recirculating flume, I will be able to quantitatively connect the sediment motion with the flow characteristics inside vegetation canopies.


Gary Lei
Graduate Student
(Email: garylei (at) mit.edu)

My project aims to understand how the rate of nutrient flux to the plant changes with the motion and posture of individual blades. The impacts of neighboring blades on nutrient flux will also be examined. I will work with both meadow and model blades which are constructed from low-density polyethylene (LDPE).  The LDPE blade can absorb chemicals injected in the flume water, to simulate the nutrient-uptake of sea grass and freshwater macrophytes. This project will extend existing models for drag /flux to individual blades in current, and also explore a predictive model for mass flux based on different flow conditions.


Ying "Helen" Shi
Visiting Graduate Student
(Email: yingshi (at) mit.edu)

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.




Chao Liu
Visiting Graduate Student
(Email: chaoliu (at) mit.edu)
State Key Laboratory of Hydraulics and Mountain River Engineering
Sichuan University, Chengdu, China

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. However, these studies have considered a limited range of velocity. I will consider a broader range of channel velocity, and specifically including conditions in which stem turbulence disappears with the patch, so the turbulence intensity in the wake decreases significantly. This is different from previous studies with 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 mainly explore the change in the pattern of sediment deposition with gradually decreasing upstream velocity, and I discuss some specific phenomena in the low velocity case. Flow visualization using fluorescein and blue lighting is used to visualize the flow through the patch and how it diffuses after escaping from the patch.


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