From Meadow to Micro: Using Experimental Fluid Mechanics to Study Seagrass Beds and Oil Spills

Tracy Mandel
Postdoctoral Scholar

University of California, Merced

Friday, Mar. 22, 2019, 3:10pm
Chase 105

Many processes in our environment are governed by physics: the seasonal overturning of a lake, the breaking of waves over coral reefs, and even the waving of wheat in a farmer’s field. In this presentation, I will focus on two problems in environmental fluid mechanics, and how we study them in an idealized laboratory environment. First, I will discuss the first step in remote characterization of seagrass beds by studying the overlying water surface. Flow through a seagrass bed can generate large overturning vortex structures, which cause small perturbations in the water surface slope. Using laboratory experiments, we are able to generate a parameterized model to reconstruct within-canopy velocity profiles solely from water surface measurements, suggesting that the subsurface hydrodynamics and geometry can be predicted by measuring the water surface behavior alone.

Second, I will address the role of stratification and interfacial surface tension in subsurface trapping of oil well leaks. As a droplet of oil rises in the ocean, it encounters fluid of varying density, and can become trapped as an intrusion layer in a region of strong density gradients. We find that for drop Froude numbers less than 1, fluid entrainment and drop retention are significant, as the buoyancy timescale (1/N) is less than the timescale of drop motion (U/d). For larger Froude numbers, the drop behaves as if it is in a homogeneous fluid and retention is minimal. We expect this scaling to have applications in other microscale dynamics, such as natural oil and gas seeps in coastal waters, and in the behavior of particulates and biota in stratified benthic boundary layers.

Through these two case studies, I will demonstrate the laboratory tools we use, and how results obtained in a tank in the lab can be applied to their associated real-world setting. I hope the audience will gain an appreciation of the utility of idealized fluid mechanics experiments in isolating, studying, and furthering our understanding of the physics of our environment.


Tracy Mandel received her M.S. and Ph.D. in Environmental Fluid Mechanics and Hydrology from Stanford University in 2013 and 2018, and a B.S. in Environmental Engineering from Cornell University in 2012. She is currently a postdoctoral scholar at the University of California, Merced, where her research focuses on the dynamics of oil plumes rising in stratified fluids. Her broader research interests include coastal processes, experimental methods in fluid dynamics, and the hydrodynamic signatures of aquatic ecosystems.