Open AccessThe dynamics of infragravity wave transformation over a fringing reef
Author(s) -
Pomeroy Andrew,
Lowe Ryan,
Symonds Graham,
Van Dongeren Ap,
Moore Christine
Publication year - 2012
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2012jc008310
Subject(s) - infragravity wave , geology , reef , fringing reef , crest , surf zone , waves and shallow water , wave setup , wave height , kondratiev wave , wind wave , shore , seismology , dissipation , shoaling and schooling , oceanography , geophysics , wave propagation , physics , mechanics , mechanical wave , longitudinal wave , quantum mechanics , thermodynamics
A 3 week field study was conducted to investigate the dynamics of low‐frequency (infragravity) wave motions over a fringing reef at Ningaloo Reef, Western Australia. Short‐period wave motions (0.04–0.2 Hz) were observed to dissipate on the reef crest beyond which infragravity wave motions (0.004–0.04 Hz) gradually dominated toward the lagoon. However, both the short waves and the infragravity waves were relatively small (both <0.3 m) on the reef flat owing to the shallow water depth (<2 m). The results revealed that the surf zone generation of free infragravity wave motions on the steep (∼1:20) fore‐reef slope was dominated by breakpoint forcing (as opposed to shoaling bound waves), which was also supported by detailed numerical simulations of the generation process. This is consistent with theory suggesting the efficiency of the breakpoint forcing mechanism should be high in this steep‐slope regime. Shoreward propagating infragravity waves traveled across the reef but were damped by bottom friction dissipation; however, this was at a rate much smaller than experienced by the residual short waves. With these rates of frictional dissipation also strongly dependent on the water depth over the reef, the infragravity wave heights increased at higher water levels and hence were strongly modulated by the tide. Due to the strong dissipation of infragravity waves over this wide and shallow reef that is hydraulically rough, any seaward propagating infragravity waves that reflected at the shoreline were small, leading to the dominance of progressive (shoreward propagating) infragravity wave motions throughout the reef and lagoon.