of numerical solution of the Boussinesq equations with additional terms, which
parametrically describe the energy losses during wave breaking. This method of the
solution of the hydrodynamic problems of the coastal zone is undoubtedly promising after eliminating some disadvantages in the existing models related to our
poor knowledge of the group structure of waves and infragravity waves and their
influence on the circulation in the coastal zone.
Lack of a clear qualitative picture of nonlinear deformation of irregular waves
frequently leads to incorrect interpretation of the experimental data. For example,
paradoxes appear like anomalous dispersion of waves (Kuznetsov and Speranskii
1994), which contradicts the generally accepted concepts about non-dispersive
wave motion in limiting shallow water. Despite the fact that the Boussinesq
equations quite well describe the propagation of irregular waves, the group velocity
in the existing models is ignored and the comparison of numerical simulations with
the experiment is performed only using the time averaged wave parameters. The
existence of the group wave structure and infragravity waves in the natural conditions with a broad spectrum of their scales leads to indefiniteness and frequently to
the arbitrary selection of the time needed for averaging and obtaining reliable
estimates.
The energetic concept is generally used to calculate the sediment transport
normal to the shore and along the shore. According to this concept, sediment
transport is determined through the dissipation of the wave energy. The Baillard
model developed in 1981 is most frequently used for these calculations (Bailard
1981). Detailed verification of the basic principles of this model on the basis of the
field data and spectral and cross-spectral analyses showed that at its best it makes
possible to estimate only the order of magnitude of the transport (Kosyan et al.
1999). In the most cases, the model wrongly predicts the direction of the sediment
transport normal to the coast at the frequencies of wind and infragravity waves. The
contribution of sediment transport at these frequencies to the total sediment transport normal to the shore is especially sensible in the zone of wave breaking. The
main mass of sediments is transported in this zone during storms and leads to the
morphodynamic changes in the underwater slope and the coastline. The main cause
of the divergence is in the fact, that the energetic models are based only on the
general physical approach that the sediment transport is proportional to the wave
energy dissipation without the account for the actually observed mechanisms of the
suspension deposits from the bottom existing in the nature. In addition, they do not
take into account the intermittency of the sediment transport and their dependence
on the group structure of waves; they skip variations in the spectral composition of
individual waves and phase shifts between the velocity of water, parameters of
turbulence, and concentration of suspended sediments (Kosyan et al. 1997).
A number of morphodynamic models have been published by present, which use
various approaches to the description of the actual mechanisms applied to different
regions of the coastal slope. The majority of them are related to the conditions of
regular wave forcing applied to the uniform alongshore slope formed of sand
sediments uniform by size. Under these conditions, compensation countercurrent
is considered one of the main mechanisms of sediment transport along the slope
128
R.D. Kosyan and B.V. Divinskiy
parametrically describe the energy losses during wave breaking. This method of the
solution of the hydrodynamic problems of the coastal zone is undoubtedly promising after eliminating some disadvantages in the existing models related to our
poor knowledge of the group structure of waves and infragravity waves and their
influence on the circulation in the coastal zone.
Lack of a clear qualitative picture of nonlinear deformation of irregular waves
frequently leads to incorrect interpretation of the experimental data. For example,
paradoxes appear like anomalous dispersion of waves (Kuznetsov and Speranskii
1994), which contradicts the generally accepted concepts about non-dispersive
wave motion in limiting shallow water. Despite the fact that the Boussinesq
equations quite well describe the propagation of irregular waves, the group velocity
in the existing models is ignored and the comparison of numerical simulations with
the experiment is performed only using the time averaged wave parameters. The
existence of the group wave structure and infragravity waves in the natural conditions with a broad spectrum of their scales leads to indefiniteness and frequently to
the arbitrary selection of the time needed for averaging and obtaining reliable
estimates.
The energetic concept is generally used to calculate the sediment transport
normal to the shore and along the shore. According to this concept, sediment
transport is determined through the dissipation of the wave energy. The Baillard
model developed in 1981 is most frequently used for these calculations (Bailard
1981). Detailed verification of the basic principles of this model on the basis of the
field data and spectral and cross-spectral analyses showed that at its best it makes
possible to estimate only the order of magnitude of the transport (Kosyan et al.
1999). In the most cases, the model wrongly predicts the direction of the sediment
transport normal to the coast at the frequencies of wind and infragravity waves. The
contribution of sediment transport at these frequencies to the total sediment transport normal to the shore is especially sensible in the zone of wave breaking. The
main mass of sediments is transported in this zone during storms and leads to the
morphodynamic changes in the underwater slope and the coastline. The main cause
of the divergence is in the fact, that the energetic models are based only on the
general physical approach that the sediment transport is proportional to the wave
energy dissipation without the account for the actually observed mechanisms of the
suspension deposits from the bottom existing in the nature. In addition, they do not
take into account the intermittency of the sediment transport and their dependence
on the group structure of waves; they skip variations in the spectral composition of
individual waves and phase shifts between the velocity of water, parameters of
turbulence, and concentration of suspended sediments (Kosyan et al. 1997).
A number of morphodynamic models have been published by present, which use
various approaches to the description of the actual mechanisms applied to different
regions of the coastal slope. The majority of them are related to the conditions of
regular wave forcing applied to the uniform alongshore slope formed of sand
sediments uniform by size. Under these conditions, compensation countercurrent
is considered one of the main mechanisms of sediment transport along the slope
128
R.D. Kosyan and B.V. Divinskiy