Coastal hydrodynamics beyond the surf zone of the south Baltic Sea

The paper presents experimental and theoretical investigations of hydrodynamic processes in a coastal region located close to the seaward boundary of the surf zone. The analysis is based on field data collected near Lubiatowo (Poland) by measuring equipment operated simultaneously by the Institute of Hydro-Engineering of the Polish Academy of Sciences (IBW PAN) and the Maritime Institute in Gdańsk (IMG). The data consist of wind velocity and direction measured at the IBW PAN Coastal Research Station (CRS) in Lubiatowo, deep-water wave buoy records, current profiles and sea bottom sediment parameters. Mean flow velocities measured in the entire water column have almost the same direction as wind. Nearbed flow velocities induced by waves and currents, as well as bed shear stresses, are modelled theoretically to determine sediment motion regimes in the area. It appears that the nonlinear wave-current interaction generates bed shear stresses greater than those that would result from the superposition of the impacts of waves and currents separately. The paper discusses the possibility of occasional intensive sediment transport and the occurrence of distinct seabed changes at greater coastal water depths adjacent to the surf zone. It was found that this can happen under the joint influence of waves and wind-driven currents.