Application of two coastal profile evolution models to Lubiatowo, Poland and La Barrosa, Spain

Two contrasting coastal profile models are applied to three bathymetries including a uniform gradient beach and natural profiles (multi-barred and multi-stepped) obtained from Lubiatowo, Poland and La Barrosa, Spain. The first model, developed at the Institute of Hydro-Engineering of the Polish Academy of Science (IBW PAN) (Poland), couples a quasi-3D model for nearshore hydrodynamics with a quasi-phase resolving sediment transport model which considers transport in the bed load, contact load and outer layers. The second model (PLYMPROF), developed at the University of Plymouth (UK), couples a relatively simple wave transformation model with a new abstracted description of cross-shore sediment transport beneath waves. A variety of model simulations are described, including simple runs with uniform wave forcing (up to 50 days in duration using PLYMPROF) and runs with parameterized wave forcing (wave height and wave period in deep water) for periods with one or two storm events (6-11 days total duration). Both models coped well with the different initial profiles and with uniform and time-varying wave conditions. The results of the simulations suggest that onshore-directed sediment transport in the shoaling and outer surf zones is dominant for the cases considered. Compared to the IBW PAN model, the PLYMPROF model results (using coefficients from a separate study of bar evolution at Duck, USA) show larger offshore-directed transport in the inner surf zone associated with return flow, with the overall sediment transport pattern located considerably closer to the shore. Alteration of a single coefficient in the PLYMPROF model shifts the predicted transport pattern seawards, but also results in enhanced offshore-directed transport. Despite differences in predicted cross-shore sediment transport the two models produced surprisingly similar trends in overall profile evolution suggesting that feedback between existing bathymetry and the sediment transport pattern may exert a major control on profile development. Results also suggested that bar migration patterns cannot be simply related to the occurrence or absence of storm conditions, but rather depend more subtly on the exact placement of wave breaking locations in relation to existing bars. Incorporation of tidal water level variations for La Barrosa produced small changes in model predictions, with tidal migration of the sediment flux pattern suppressing the development of bar morphology in line with the form of the observed profile.