UNH Ocean Seminar

Biophysical Drivers of Sedimentation in Salt Marsh Environments with Implications for Coastal Resiliency

Tom Lippmann

Earth Sciences and Ocean Engineering

Friday, Dec. 1, 2023, 3:10pm
Chase 105

Natural infrastructure such as salt marshes, mangroves, and other coastal wetlands are critically important to maintaining a healthy coastal ecosystem and protecting our communities from storms.  Although it has long been known that salt marshes are effective sediment traps and that they increase in elevation over time, the current rates of sedimentation are generally not high enough to keep up with sea level rise estimates.  The projected result is a change in the nature of the system, including transitions from high marsh to low marsh, and low marsh to mud flat, both of which dramatically alter the estuarine habitat, reduce (or even eliminate) ecosystem services provided by a healthy marsh ecosystem, and negatively impact resiliency of coastal communities including increased flood risk and storm damage.  Given these pressures, communities need strategies for maintaining and building natural infrastructure. One strategy is a so-called mud motor where the injection of sediments into flooding tides might build marshes, and will require an understanding of the how suspended sediment is dispersed and deposited in complex vegetated systems.  The goal of our effort is to address these needs with a combination of small- and large-scale field and laboratory studies, and with numerical simulations that include publicly available hydrodynamic flow models.  Progress in these areas will be discussed, including preliminary results from field experiments conducted in New Hampshire’s Hampton/Seabrook Estuary (HSE) in the summer and fall of 2023, and numerical simulations using the Regional Ocean Modeling System (ROMS) and offline particle tracking algorithms.  Field experiments include GPS surface drifter deployments needed to estimate dispersion coefficients for particle transport simulations, and initial florescent dye tracing with drone-based hyperspectral cameras.  Larger scale observations of fluid flows and water levels are used to verify the ROMS simulations.  Finer scale observations of water levels (sea surface slopes), mean flow, turbulence, dissipations rates, and turbidity were obtained in focused deployments across a single transect that spans the mud flat, low marsh, and into the high marsh.  Ancillary observations include plant properties (vegetation stalk dimensions, density, and canopy height), surface elevation tables (SETs) for marsh building (sedimentation rates), and sediment grain size distributions.  As we progress through the program, results will provide insight into salt marsh sedimentation processes and rates across the estuary with implications to long term coastal resiliency under sea level rise, and will improve understanding of salt marsh vegetation response to increased sedimentation that will provide guidance to managers developing coastal resilience strategies.


Tom Lippmann is a nearshore oceanographer with affiliation with the Department of Earth Sciences and the Ocean Engineering program. He received a BA in Mathematics and Biology from Linfield College (1985), and an MS (1989) and PhD (1992) in Oceanography at Oregon State University. His dissertation research conducted within the Geological Oceanography Department was on shallow water physical oceanography and large scale coastal behavior. He went on to do a Post Doc at the Naval Postgraduate School (1992-1995) in Physical Oceanography.

He worked as a Research Oceanographer at Scripps Institution of Oceanography (1995-1999) in the Center for Coastal Studies, and retains a research associate with the Integrated Oceanography Division at SIO. He was then a Research Scientist at Ohio State University (1999-2008) jointly in the Byrd Polar Research Center and the Department of Civil and Environmental Engineering and Geodetic Science.

Dr. Lippmann's research is focused on shallow water oceanography, hydrography, and bathymetric evolution in coastal waters spanning inner continental shelf, surf zone, and inlet environments. Research questions are collaboratively addressed with a combination of experimental, theoretical, and numerical approaches. He has participated in 14 nearshore field experiments and spent over 18 months in the field.