PHASE-LOCKING OF MODES IN THE NEARSHORE: FIELD EVIDENCE

J.W. Haines, A.J. Bowen

Abstract


Field investigations have shown that infragravity frequencies may dominate nearshore fluid motions (Bowen and Huntley, 1984). Theoretical studies have suggested that the modal structure of the infragravity field, including the degree of modal coupling, is important in generating complicated beach morphologies (Holman and Bowen, 1982) but previous analyses of field data have not provided a description of the infragravity field which is sufficiently detailed to assess the importance of these ideas. In this paper we present a statistical method which, when applied to data from any large sensor array, provides the desired description of the infragravity field. The method is applied to data from the NSTS (Nearshore Sediment Transport Study) experiment. The variance of the observed velocity field is described by a set of free wave modes. The results indicate that a complicated infragravity field composed of both edge waves and leaky modes is present. The modes modelled are also found to be significantly coupled over a range of modal pairs and frequencies.

Keywords


field evidence; phase-locking modes

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