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| Titel |
Typical scenarios of nonlinear wave transformation: criteria of realization and contribution in relief changes. |
| VerfasserIn |
Margarita Shtremel, Yana Saprykina, Sergey Kuznetsov, Nataliya Andreeva |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250086490
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| Publikation (Nr.) |
 EGU/EGU2014-368.pdf |
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| Zusammenfassung |
| Coastal zone is area which dynamical regime is formed by wind waves. While propagating to
the coast, waves are transforming and then breaking. All energy of waves brought from deep
water dissipates in coastal zone causing bottom sediment suspension. Wave asymmetry,
which determines bulk and direction of sediment transport, also changes. These
processes lead to bottom relief deformations, such as bar formations, beach erosion or
accumulation. Occurrence of each situation depends on wave regime and mean bottom
slope.
Purpose of this work is to find typical examples of manifestation of nonlinear wave
transformation and to account its contribution to relief changes. This investigation can be
used to classify coastal zones and estimate their vulnerability to wave impact.
Waves in coastal zone are weakly nonlinear dispersive due to near-resonant triad
interactions between wave components. The main feature of nonlinear wave transformation in
intermediate depth is periodical exchange of energy between first and higher harmonics of
wave motion. This effect causes fluctuations of higher statistic moments of waves. The
periodical fluctuation of amplitudes of nonlinear wave harmonics was used to develop
classification of coastal zone.
“Skorpilovtsy-2007” field experiment data was analyzed and four scenarios of
nonlinear wave transformation were determined. They were separated from one
another depending on character of energy exchange between first and second wave
harmonics:
1. Input waves have low second harmonics, their amplitude grows only near the shore 1,5
– 2 periods of energy exchange can be distinguished
2. There is only one full period of energy exchange with high relative amplitude of second
harmonic. Second harmonic reaches its maximum within coastal zone
3. There is no obvious maximum of second harmonic and its amplitude changes very little
in whole coastal zone. There are 3 and more periods of energy exchange.
4.Amplitude of the second harmonic on the seaward end of the coastal zone is quite
high and decreases to the shore so nearly half of a period of energy exchange is
observed.
It was found that Iribarren number (bottom slope to square root of wave steepness ratio)
can be used as criterion of separation of these scenarios. Iribarren number less than 0,15
correspond to significant development of nonlinear effects in coastal zone (Saprykina et al.,
2013) which is characterized by second harmonic amplitude reaching its maximum inside
coastal zone and having big relative amplitudes.
Values of cross-shore sediment transport for previously distinguished scenarios were
computed in all points of measurement across the coastal zone using simplified Bailard
formula (Bailard, 1981).
Each scenario causes different qualitative type of relief deformation: first – erosion of the
bottom slope and sediment transport to the shore, second – send bar migration to
the coast by erosion of its crest, third – the same effect, but because of seaward
slope erosion, and the last – degradation of the bar and sediment transport to the
shore.
Field experiment data analysis shows that sediment transport induced by wave
asymmetry is always directed to the shore. Different scenarios determine bar migration or
degradation. |
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