Research

Our research focuses on fundamental and applied problems in environmental fluid mechanics, and is funded by the National Science Foundation, U.S. Coastal Research Program, Office of Naval Research, Air Force Office of Scientific Research, and New Hampshire Sea Grant. See below for a description of our main three research thrusts.

(1) Connecting free-surface and subsurface turbulence dynamics

Mixing and surfacing dynamics in buoyancy-driven systems

Plumes and particles in the marine environment can interact strongly with the ambient ocean water column. We are interested in the surfacing of and mixing dynamics of turbulent buoyant plumes, such as those found in subglacial discharge plumes and industrial outfalls, and how this fundamental problem in fluid mechanics relates to dynamics observed in the field. Prior work has studied the trapping of droplets and oceanic particles in stratified flows.

Related publications:
Saeed, Z., White, C.M., and Mandel, T.L. (2025). On the physical dimension of the turbulent sublayer at the turbulent/non-turbulent interface. Journal of Turbulence 26(5): 174-195.
Saeed, Z., Weidner, E., Johnson, B.A., and Mandel, T.L. (2022). Buoyancy-modified entrainment in plumes: Theoretical predictions. Physics of Fluids 34: 015122 [doi]
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]

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). We are 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.

Ongoing work at UNH is funded by the Office of Naval Research award no. N00014-21-2-2669.

Related publications:
Bheeroo, V. & Mandel, T.L. (2023). Comparison of Schlieren-based techniques for measurements of a turbulent and wavy free surface. Experiments in Fluids 64: 114. [doi]
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]

Vortex-surface interactions

In this project, we are working to understand the interaction of counter-rotating vortex pairs, which can be shed by underwater vehicles or subsurface obstructions, with the free surface. We are combining experimental measurements of free-surface elevation and temperature with subsurface dye visualization and velocity fields to better understand surface-subsurface connections.

This project is in collaboration with Dr. Sarah Morris and her group at Montana State University, and funded by Air Force Office of Scientific Research award no. FA9550-24-1-0211.

(2) Improving ecosystem health and monitoring by understanding physical processes in benthic ecosystems

Flow-mediated transmission of disease in benthic ecosystems

Marine pathogens can decimate ecosystems and severely impact coastal communities and economies that rely on marine organisms and their ecosystem services. In this project, we are working to understand the physical mechanisms driving local, patch-scale disease transmission in seagrass and coral ecosystems, and how we can better predict and prevent marine disease outbreaks.

This project is funded by an NSF CAREER Award through the Biological Oceanography Program, award no. 2339079.

Connecting seagrass seed transport with genetic distributions

Genetic diversity in eelgrass influences both short- and long-term resilience to environmental change. However, the effects of hydrodynamics on the genetic diversity and structure on eelgrass populations is poorly understood. We are working with collaborators to study the transport of anisotropic seed particles in a model eelgrass bed in order to dvelop parameterizations of seed distribution based on release location and flow/meadow characteristics.

This project is in collaboration with Dr. Theresa Oehmke and Dr. Tom Lippmann at UNH and Dr. Cynthia Hays at Keene State College, and funded by New Hampshire Sea Grant and the U.S. Coastal Research Program. Photo by Tim Briggs, N.H. Sea Grant.

Impacts of plant motion on light availability in seagrass

Seagrass health and biomass production is a function of light exposure and photosynthesis rates, which require knowledge of the variable light environment within a meadow. However, realistic plant motion will have a complex impact on within-canopy shading in submerged vegetation. In this project, we have applied simple optical analysis to modelled plant motion, finding that while meadow geometry is a controlling parameter, flow-induced reconfiguration is also important to parameterizing light exposure.

This project is in collaboration with Dr. Longhuan Zhu of the Sustainable Seafood Systems Center at UNH.

Related publications:

Mandel, T.L. & Zhu, L. (2025). Wave-driven plant reconfiguration modifies light availability in seagrass meadows. Limnology & Oceanography 26(5): 174-195.

(3) The role of coastal vegetation in cold-weather climates

Sediment transport in salt marshes

Salt marshes are highly effective sediment traps and historically accrete and increase in elevation over time. However, current rates of sedimentation in the Hampton-Seabrook Estuary are not enough to keep up with sea level rise, which will lead to transitions in low and high marsh habitats and ecosystem services. We are studying fine-scale sediment transport in a field transect in HSE to better understand sedimentation processes in vegetated environments.

This work is in collaboration with Dr. Tom Lippmann, Dr. David Burdick, and Dr. Diane Foster at UNH, and funded by the U.S. Coastal Research Program.

Biomechanics of coastal plants

Marsh and dune vegetation reduce flow velocities and helps sediment settle. Plant stiffness plays an important role in this process. In coastal flood modeling, if vegetation is parameterized with a single value that is constant and time in space, we may over- or under-estimate the protective benefits of marsh and dune plants.

In this project, we are studying how seasonal plant life-cycle changes (such as stem stiffness, plant height, and plant density) affect flow and sediment transport, using field measurements of plant stiffness over time, and the development of a tunable-stiffness plant mimic for laboratory studies.

This work is in collaboration with Dr. Theresa Oehmke at UNH, and has been funded by the U.S. Coastal Research Program and New Hampshire Sea Grant.

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