Three Tree Point

Headland Eddy Formation and Dissipation 

at Three Tree Point, Washington

Funded by the National Science Foundation Grants OCE-0099058 and OCE–04255893

Coastal stirring, caused by the interaction of tidal currents with complex bathymetry, is important to the dispersal of plankton, larvae, and pollutants. It may also exert a large form drag on alongshore currents.  Our numerical and theoretical work on stratified flow past a headland on a slope allows us to predict whether a given headland will be more likely to produce internal waves or horizontal eddies. In either case the pressure drag on the headland is substantial. Previous laboratory studies (Pawlak and MacCready, 2002) of homogenous tidal flow past a headland indicate that if headland eddies persist longer than a tidal cycle the resulting eddy interactions may give rise to a residual flow from offshore toward the headland, opposite to the result for tidal headland flow with high dissipation.

This project, funded by NSF, used field observations and numerical modeling to examine the formation and dissipation of a headland eddy in deep water.  Included in this is examination of the vertical structure of vorticity within an eddy and of the baroclinic response of the flow around the sloping headland.  Field observations used subsurface drogued drifters to follow individual eddies and examine the horizontal dispersion pattern, along with boat-mounted ADCP and CTD surveys which measure the 3-D flow structure over the tidal period. 

Three Tree Point survey tracks for 3 cruises

Publications:

M. Canals and G. Pawlak, "Three-dimensional vortex dynamics in oscillatory flow separation", Journal of Fluid Mechanics, 674, pg 408, doi:10.1017/S0022112011000012, 2011

M. Canals, G. Pawlak and P. MacCready, “Tilted Baroclinic Tidal Vorticies”, J. Physical Oceanography, 39, 333–350, doi: 10.1175/2008JPO3954.1, 2009\

R. McCabe, P. MacCready and G. Pawlak, “Form Drag Due to Flow Separation at a Headland”, Journal of Physical Oceanography, Vol. 36, No. 11, pp. 2136-2152, 2006

K. Edwards, P. MacCready, J. Moum, G. Pawlak, J. Klymak and A. Perlin, "Form Drag and Mixing due to Tidal Flow past a Sharp Point", Journal of Physical Oceanography, Vol. 34, June 2004.

G. Pawlak, P. MacCready, K. Edwards,  and R. McCabe, "Observations of the Evolution of Tidal Vorticity at a Stratified Deepwater Headland", Geophysical Research Letters, Vol. 30, no. 24, pp. 2234, Dec. 2003.