The present study follows a conventional approach, within which seabed evolution is assumed to be taking place as a result of the
spatial variability of net sediment transport rates. These rates along the cross-shore profile depend on the instantaneous rates at each individual location during the wave period. As mentioned before, determining the instantaneous hydrodynamic and lithodynamic parameters in the region of a moveable boundary of an aquatic environment is problematic. To date, there have been a few attempts to solve this problem, and a number of more or less sophisticated theoretical and experimental approaches have SB203580 nmr been proposed and reviewed (see e.g. Butt and Russell, 2000, Kobayashi and Johnson, 2001, Larson et al., 2001, Alsina et al., 2005 and Masselink and Puleo, 2006). These studies, however, deal mostly with waves
breaking on the beach face. Nevertheless, the available studies do provide many interesting and insightful findings. For instance, Nielsen (2002) showed that the flow velocity during a rapidly accelerating up-rush generates much stronger bed shear stresses (and sediment transport rates) than the same velocity during a mildly accelerating down-rush flow. Further, this author points to a number of physical processes that complicate the problem, e.g. the lag between instantaneous bed shear stresses and instantaneous sediment transport rates, pre-suspension selleck of sediment from bore collapse see more versus very high concentrations in the sheet flow layer, as well as infiltration and fluidization. The study by Pritchard & Hogg (2005) triggers similar doubts and queries, especially concerning the qualitative and quantitative imbalance between onshore and offshore transport, dependent as this is on contributions from sediment entrained within the swash zone and that from sediment suspended by the initial bore collapse. The discussion of this issue is continued by Baldock & Alsina (2005), who anticipated distinct difficulties in further theoretical and experimental investigations into the hydro-, litho-and morphodynamics of the swash zone. Although considerable progress in swash zone modelling has
been made and some models simulating time-dependent sediment transport rates have been derived for the swash zone, it appears that knowledge of the swash zone is still far from complete: a wholly reliable, detailed description of swash zone lithodynamics has yet to be achieved. Therefore, any new proposals in this respect will be attractive only if they fill a gap in our existing knowledge of swash zone behaviour. Migration of the shoreline is caused by the incessant process during which sandy beaches are subject to erosion or accretion. The latter is less spectacular but equally important in reshaping coastal bathymetry. It is thought that accretionary conditions prevail during periods dominated by long, non-breaking waves.
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