Horizontal Eddies in the offshore zone

Li Li*, Robert A. Dalrymple

*Corresponding author for this work

Research output: Contribution to journalConference articlepeer-review


The mean flow outside the surf zone can be unstable and form a train of submerged vortices, which migrate slowly in the offshore direction, as discovered by Matsunaga, Takehara & Awaya (1988, 1994). Li and Dalrymple (1998) conducted large scale experiments and a numerical study. They showed that two layers of vortices could exist over the water depth. Eddies near the water surface rotated in the opposite direction of eddies at mid-depth. For example, for the surface wave propagating to the right, the rotation direction of eddies near mid-depth was counterclockwise, while the rotation direction of eddies near surface was clockwise. The vortices decay offshore where there was no shear layers over water depth. Experimental and numerical studies show the velocity of long time scale vortical motion is uniform over water depth and is much slower than the undertow. A theoretical analysis shows that the stresses due to turbulence and wave serve as the source of the vorticity and this vortex train is formed by the shear instabilities of the mean flow in the cross-shore direction.

Original languageEnglish (US)
Pages (from-to)175-188
Number of pages14
JournalProceedings of the Coastal Engineering Conference
StatePublished - Dec 1 1998
EventProceedings of the 1998 26th International Conference on Coastal Engineering, ICCE-98 - Copenhagen, Denmark
Duration: Jun 22 1998Jun 26 1998

ASJC Scopus subject areas

  • Ocean Engineering


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