Surface signatures of aquatic ecosystems

Characterizing and monitoring the spatial extent, health, and general characteristics of aquatic ecosystems like seagrass beds presents a challenge that evolves both in space (due to fragmentation of these habitats) and time (due to tides, seasons, and ecosystem growth). I'm therefore interested in the hydrodynamic signatures that these aquatic ecosystems leave on the water surface, as this may serve as a proxy for characteristics of the system, as well as the flow it is exposed to.

In the lab, a submerged canopy leaves a footprint on the water surface that is indicative of its relative submergence, as well as of the mean velocities within and above the canopy. This footprint is a result of the shear instability generated by a submerged canopy, which generates periodic vortex structures that eventually impact the water surface.

At UNH, we will be placing infrared cameras and other remote sensing equipment near seagrass beds in Great Bay and surrounding areas, in order to detect this same surface signature in the field. Using the new oscillating water tunnel built in 2018, we will also be conducting laboratory studies on how the flexibility of submerged vegetation affects the observed surface signature.

Mandel et al. (2019). On the surface expression of a canopy-generated shear instability. Journal of Fluid Mechanics 867: 633-660 [pdf][doi]
Mandel et al. (2017). Characterizing free-surface expressions of flow instabilities by tracking submerged features. Experiments in Fluids (11), 153 [pdf] [doi]

Plumes and particles in stratification

Plumes and particles in the marine environment can interact strongly with the ambient ocean stratification. I am interested in the trapping of oil droplets and oceanic particles in intrusion layers, as well as the surfacing of subglacial discharge (freshwater) plumes, and how this fundamental problem in fluid mechanics relates to dynamics observed in the field.

Mandel, T.L., Zhou, D.Z., Waldrop, L., Theillard, M., Kleckner, D., and Khatri, S. (2020). Retention of rising droplets in density stratification. Physical Review Fluids 5: 124803 [pdf] [doi] [data]

Measuring wave fields by tracking bottom features

In clear waters such as coral reefs, fixed roughness features at the sea bed are optically distorted by the air-water interface. We are currently developing methods to measure surface wave fields by quantifying this apparent distortion.

To learn more about our bench-scale test tank and wavemaker (image on left), check out Matthias Page's wavemaker design: