Publication Date:
2016-09-28
Description:
Two field data sets of near-bed velocity, pressure and sediment concentration are analyzed to study the influence of infragravity waves on sand suspension and cross-shore transport. On the moderately sloping Sand Motor beach (≈ 1:35), the local ratio of infragravity wave height to sea-swell wave height is relatively small ( H I G / H S W 〈0.4) and sand fluxes are related to the correlation of the infragravity-wave orbital motion with the sea-swell wave envelope, r 0 . When the largest sea-swell waves are present during negative infragravity velocities (bound wave, negative correlation r 0 ), most sand is suspended here and the infragravity sand flux q I G is offshore. When r 0 is positive, the largest sea-swell waves are present during positive infragravity velocities (free wave), and q I G is onshore directed. For both cases, the infragravity contribution to the total sand flux is, however, relatively small (〈20%). In the inner surf zone of the gently (≈ 1:80) sloping Ameland beach, the infragravity waves are relatively large ( H I G / H S W 〉0.4), most sand is suspended during negative infragravity velocities, and q I G is offshore directed. The infragravity contribution to the total sand flux is considerably larger and reaches up to ≈ 60% during energetic conditions. On the whole, H I G / H S W is a good indicator for the infragravity related sand suspension mechanism, and the resulting infragravity sand flux direction and relative importance.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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