Alumni

Visiting Postdoc from University of Twente, Netherlands

thomasvv@mit.edu

Salt marshes are vegetated coastal wetlands with benefits for coastal protection, biodiversity, and carbon sequestration. Their complex interaction between currents, waves, fine sediments, and vegetation creates a dynamic shoreline that is resilient or erosive. Resilient salt marshes have sufficient sediment deposition to withstand erosion and may even expand, whereas erosive salt marshes are shrinking and provide fewer ecosystem services. My goal is to understand how salt marsh vegetation affects sediment deposition using experiments in the Nepf Lab wave-current flume. Vegetation can reduce current and wave velocities, which may enhance deposition. However, the interaction between currents, waves and vegetation also generates turbulence, which contributes to sediment resuspension. My experiments will define different regimes for sediment deposition under conditions with combined waves and currents. The results will provide insight on sediment deposition patterns on salt marshes, and, consequently, salt marsh resilience.

Visiting Graduate Student from Dalian University of Technology
zhaocy(at)mit.edu

My research focuses on sediment transport in a submerged flexible meadow influenced by waves and current. Previous studies have shown that the near bed turbulence is the main trigger for sediment resuspension. In my study, I will measure vertical profiles of velocity and sediment concentration under different hydrodynamics conditions and uses these measurement to predict the threshold level of turbulence for sediment resuspension and deposition. Moreover, I will also consider how submerged flexible vegetation influences the formation of ripples in wave and current flow.

Undergraduate Student

slassar (at) mit.edu

When water with excess sediment flows through gravel streams it can clog the small spaces in between the gravel, known as interstitial spaces. These interstitial spaces are important for young fish, such as trout and salmon. I will work on a project modeling how sediment clogs up gravel streams, and investigate how adding obstacles (like logs, rocks, etc.) to these streams affects clogging. The turbulence created by adding these obstructions create can alleviate clogging, so this project aims to quantify if and how much clogging is prevented.

Assistant Professor National University of Singapore

garylei (at) mit.edu

Personal Website

Aquatic vegetation damps waves and currents, protecting shorelines from erosion. My research combines physical and numerical experiments to develop models that predict the impact of vegetation on wave damping, turbulence generation, and sediment fate. Read more about my work here.

Now PhD student at Penn State

autumnd (at) mit.edu

Coastal environments, such as mangrove forests, provide an unparalleled amount of ecosystem services, from water purification and flood prevention to the mitigation of climate change. In the Nepf Lab, I will investigate the critical conditions for erosion and deposition within black mangrove’s pneumatophores, which are also known as pencil roots because of their vertical and pencil-like shape. Pencil roots have an influence on sediment transport. They can both generate turbulence that can promote erosion and slow the currents near the bed that can promote deposition. If we know these critical conditions, then we can better understand the sediment fate and transport as well as how much carbon is stored in mangrove forests.

To determine these critical conditions, I am combining field work conducted in Port Fourchon, LA with laboratory methods. I will then use my observational field data and laboratory results to construct sub-grid scale models for erosion and deposition, which will be incorporated into a coastal-scale model to explore the role of channels in optimizing sediment retention within mangrove forests. 

Assistant Professor, Shenzhen University

Many natural plants are composed of leaves and stem, both of which are flexible and reconfigure (bend) in response to current and waves. The motion of plant elements impacts the plant drag, which in turn, modifies the flow structure and turbulent intensity, decreases in-canopy flow velocity, and dissipates wave energy. My research uses experiments with live and model plants, numerical simulation, and field investigation to understand the interaction of flexible plants with current and waves and to build physical-based simple predictive models for plant drag, flow structure, and wave dissipation.

MEng Student

rovi@mit.edu

Historically, logjams have been removed from rivers due to concerns of flooding, erosion, and destruction of property. However, new research has demonstrated that logjams have beneficial properties including generating pools that protect salmoniod spawing, propagule retention sites, and increasing biodiversity. For these reasons, engineered logjams are being introduced into rivers across the Northwest of the United States. To better identify the key components that enable logjams to create suitable habitat for salmonid fish, I am conducting physical experiments with model logjams. These experiments vary the dimensions and solid volume fraction of the log jam, and measure the velocity and turbulence in the wake. After characterizing the dimensional effects of the logjams, suggestions on which type of logjam is most suitable given what is known about fish preference are made. 

Asst. Professor, East China Normal University

State Key Laboratory of Estuarine and Coastal Research

yuanxu@sklec.ecnu.edu.cn

The evolution of vegetated landscape occurs through the interplay of flow, vegetation, and sediment transport. There is a lack of predictive models that accurately account for the impact of vegetation morphology on sediment transport. Most previous studies have only considered circular cylinders as a model for vegetation. My study focuses on the sediment transport in channels with realistic models of emergent cattail. First, flume experiments will be used to describe and predict the turbulence level and form drag within a canopy of cattails. Second, the incipient sediment motion will be investigated and compared with the bare channel. Finally, I will attempt to construct a theoretical model that predicts sediment transport rate in channels with different distributions of realistic cattail models.

Graduate Student

gltso (at) mit.edu

Georgette Tso is an MEng student studying green seawalls. Seawalls are a common infrastructure used to protect coastal regions from storm surge and waves. Historically, seawalls have been constructed from marine concrete blocks with smooth, vertical geometry. Because the seawalls eliminate intertidal zones, they diminish marine biodiversity. To make seawalls more hospitable to marine fauna, researchers have introduced texture and shapes to seawall surfaces, and introduced concrete mixes with enriched levels of CaCO3. This study will compare marine cement and enriched cement for the attributes of recruitment rate and durability (measured through changes in material strength). The study can inform installation choices for optimizing green seawall design. Knowledge of recruitment and durability under high wave exposure is particularly relevant to future Boston-area developments.

Graduate Student

Current Position: PhD student, Wuhan University

jiaoz (at) mit.edu

My research examines turbulence and sediment transport in flows with submerged vegetation. Turbulence can be generated by the wakes of individual plants. In addition, the velocity is redistributed by submerged vegetation, and a shear layer is formed at the top of the canopy, which generates canopy-scale turbulence.