Shoreline dissipation of infragravity waves
In: Continental Shelf Research. Pergamon Press: Oxford; New York. ISSN 0278-4343; e-ISSN 1873-6955, more
|  |
| Keyword |
|
| Author keywords |
Infragravity waves, Energy flux, Reflection, Dissipation, Wave breaking |
| Authors | | Top |
- de Bakker, A.T.M.
- Tissier, M.F.S.
- Ruessink, B.G.
|
|
|
| Abstract |
Infragravity waves (0.005–0.05 Hz) have recently been observed to dissipate a large part of their energy in the short-wave (0.05–1 Hz) surf zone, however, the underlying mechanism is not well understood. Here, we analyse two new field data sets of near-bed pressure and velocity at up to 13 cross-shore locations in ≲2:5 m depth on a ≈ 1 : 80 and a ≈ 1 : 30 sloping beach to quantify infragravity-wave dissipation close to the shoreline and to identify the underlying dissipation mechanism. A frequency- domain Complex Eigenfunction analysis demonstrated that infragravity-wave dissipation was frequency dependent. Infragravity waves with a frequency larger than ≈ 0:0167–0:0245 Hz were predominantly onshore progressive, indicative of strong dissipation of the incoming infragravity waves. Instead, waveswith a lower frequency showed the classic picture of cross-shore standing waves with minimal dissipation. Bulk infragravity reflection coefficients at the shallowest position (water depth ≈ 0:7 m) were well below 1 (≈ 0:20), implying that considerable dissipation took place close to the shoreline.We hypothesise that for our data sets infragravity-wave breaking is the dominant dissipation mechanism close to the shoreline, because the reflection coefficient depends on a normalised bed slope, with thehigher infragravity frequencies in the mild-sloping regime where breaking is known to dominate dissipation. Additional numerical modelling indicates that, close to the shoreline of a 1:80 beach, bottom friction contributes to infragravity-wave dissipation to a limited extent, but that non-linear transfer of infragravity energy back to sea–swell frequencies is unimportant. |
|
