Wave group forcing of low frequency surf zone motion

Merrick C. Haller*, Uday Putrevu, Joan Oltman-Shay, Robert A. Dalrymple

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


The nearshore potential vorticity balance of Bowen and Holman (1989) is expanded to include the forcing from wave group-induced radiation stresses. Model results suggest that the forcing from these radiation stresses can drive oscillations in the longshore current that have a spatial structure similar to linear shear instabilities of the longshore current. In addition, the forced response is nearly resonant when the forcing has scales (k, σ) similar to the linearly most unstable mode. Thus, we suggest that wave groups may provide an initial perturbation necessary for the generation of shear instabilities of longshore currents and also act as a source of vortical motions on beaches where linear instabilities are completely damped. Data from the SUPERDUCK (1986) field experiment were analyzed for the presence of spatially coherent wave groups. The analysis confirms that wave groups with periods and longshore spatial structures comparable to the observed shear wave motions were sometimes present on this open coast. This indicates that wave groups with the required spatial and temporal structure to initiate the low frequency oscillations in the longshore current can exist.

Original languageEnglish (US)
Pages (from-to)121-136
Number of pages16
JournalCoastal Engineering Journal
Issue number2
StatePublished - Jun 1999


  • Instabilities
  • Longshore current
  • Shear waves
  • Vorticity
  • Wave groups

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Modeling and Simulation
  • Ocean Engineering


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