Science Seminar Series

Check out our archive of past seminars.

Tuesday, May 18, 2021 10:00am PDT

Benjamin K Norris, PCMSC

Small-scale Turbulence and its Influence on Forest-scale Morphodynamics within a Coastal Mangrove Forest

Join seminar via Microsoft Teams

Abstract: Growing in the interface between the coastal ocean and land, mangroves form a barrier to hazards such as wave attack, coastal flooding and erosion for many densely-populated areas that often lack hard coastal defense structures. By damping tidal currents and waves, mangroves also facilitate sedimentation, and may contribute to coastal stability in the face of rising sea levels. These valuable ecosystem services are the result of characteristic bio-physical feedbacks between the mangrove vegetation, hydrodynamics and sediment dynamics within intertidal zone. 

Here, the link between mangrove root density and turbulent dissipation was explored in a coastal mangrove forest that is exposed to a dynamic wave environment and tidal forcing. Measurements of turbulent kinetic energy (TKE) dissipation were collected at millimeter scales within clusters of mangrove pneumatophore roots (‘canopies’) spanning the unvegetated mudflat to the densely vegetated forest. High-resolution root geometries were reconstructed using a newly developed photogrammetric method and were compared with turbulence measurements. Across the forest, turbulence was positively correlated with root density and wave height and was negatively correlated with water depth. At small (1 m2) scales, high near-bed turbulence was the result of Von Kármán vortices shedding off upstream roots, and enhanced turbulence above the canopy was associated with velocity shear. Across small (1 m2) and forest scales, measurements demonstrated that the spatial variability in vegetation density was also a control on sediment transport. Waves were dissipated by the vegetation as they propagated landward, but dissipation at infragravity periods (> 30 s) was observed to be less than dissipation at shorter periods (< 30 s). Consequently, infragravity-frequency fluctuations in the bed level adjacent to the mangrove roots suggest that infragravity waves may help drive sediment transport in mangroves.

Tuesday, June 1, 2021 10:00am PDT

Jon Nye

Ecological Crisis in the Salton Sea

Tuesday, June 8, 2021 10:00 PDT

Coastal Change Hazards Seminar, hosted by St. Petersburg Coastal and Marine Science Center

Tuesday, June 15, 2021 10:00am PDT

Richard (Rip) Hale

Sediment Dynamics of the Ganges-Brahmaputra Delta, Bangladesh

Natural Bridges State Beach, shown here in the middle of the photo, is nestled amongst coastal neighborhoods in the southwestern part of Santa Cruz, California. View is looking south. The offices of the USGS Pacific Coastal and Marine Science Center are just a few hundred feet north, outside the bottom portion of the photograph.

Photo by Laura Torresan