Shear Instabilities & Spatial Variability of Tidal Currents in Estuarine Channels

Katie Kirk
Ph.D. Dissertation Proposal Defense

Earth Sciences Department, Oceanography

Tuesday, Apr. 27, 2021, 10:10am

Tidal currents flowing through narrow estuarine channels can have horizontal velocity gradients that produce instabilities in the flow. The instabilities manifest into alongshore progressive shear waves growing exponentially in time causing a meandering of the along channel mean current. The resulting eddies may impact navigation, transport of organic and inorganic matter (e.g. larvae, oil spills, etc.), and cause horizontal mixing of momentum in coastal estuaries. Instabilities may also impact energy resource assessments renewable energy initiatives as mean kinetic energy is lost to turbulent kinetic energy through the development of unstable eddies. In this research, the theory for the existence of linear instabilities in laterally sheared depth-integrated tidal currents is derived for arbitrary topography including linear bottom friction. Observations will be collected to compare the shear wave spectra to the fastest growing unstable modes predicted by the analytical solutions. In the third chapter, a hydrodynamic numerical model will be implemented to examine the spatial variability and the significance of those variations about the mean tidal current. Numerical experiments will be run over various horizontal grid scales to determine the required resolution necessary in a constricted estuary to resolve flow features of significance to marine navigation and other NOAA model end users. Simulations will be conducted over both idealized and realistic topography that approximates natural field conditions in the Piscataqua River in order to qualitatively assess the forcing conditions that produce the observed spatial structure of the mean along-channel tidal currents. 

Committee: Tom Lippmann (Chair), Diane Foster, Jamie Pringle, Greg Dusek (NOAA), John Kelley (NOAA/UNH CCOM)


Katie Kirk earned a B.Sc. in Science of Earth Systems with a concentration in Ocean Sciences from Cornell University. She went on to earn a Master of Engineering in Ocean Sciences & Technology in a joint program between Cornell University and Woods Hole Oceanographic Institution. Katie has participated in various oceanographic research cruises and previously worked as the Lead Engineering Technician of the NOAA Chesapeake Bay Interpretive Buoy System. Katie currently works as an Oceanographer for NOAA National Ocean Service's Center for Operational Oceanographic Products and Services (CO-OPS) on the Coastal and Estuarine Circulation Analysis Team (CECAT). At CO-OPS, she primarily works as a project lead of current surveys along the coastal U.S. in an effort to update the tidal current predictions. Katie will continue working in her role with NOAA while pursuing a Ph.D. in Oceanography at UNH as an advisee to Dr. Tom Lippmann.