A new concept of statistical analysis of multibar profiles is presented in the study; vertical residuals about a reference Dean curve are treated as sine functions with random amplitude (envelope), bar wave number and phase. The data set consists of 71 transects, collected from 1964 to 1994 by the Polish Academy of Science, Institute of Hydro-Engineering, Coastal Research Facility at Lubiatowo (CRF), situated some 80 km northwest of Gdańsk. The morphology of the nearshore zone there is typical of the south Baltic Sea and is characterized by a mild slope (m= tan α≈ 1.0) and fine sand sediment D₅₀= 0.22 mm). Because the Baltic Sea is semiisolated from the Atlantic, no tides can be observed, and beach profiles are mostly subject to wave attack and storm surges. The envelope of random sine functions (RSF) describes mean deviation about a Dean reference profile with respect to its location on the profile. Thus, it depicts vertical cross-shore variability, which may be useful for determination of wave breaking zones where the profile variability is especially intensive (envelope peaks). Bar wave numbers characterize bar lengths and distances between bars along the profile. Multibar cross-shore profiles can thus be analysed by means of only two parameters, based on very simple RSF methodology. The random sine function method poses an alternative in multibar beach profile description with respect to empirical orthogonal functions, because it seems to be less ambiguous in many cases. The results of the study contain empirical relationships, which depict bar lengths on a multibar profile, and vertical deviations about the reference profile, which can be regarded as assessment of bar height.

A method of analysis of depth of closure and bed variability is presented in the study. Statistical analysis of measurements showed standardized depths are gaussian random variables Repetitive measurements revealed peaked patterns of standard deviation of depth change and range between extreme measurements. They were approximated by a smooth functional type inform of a sum of exponential curves. The peaks were then associated with both the corresponding time scales and locations of bed features. The patterns can thus be used to identify segments of beach profiles controlled by events typical of given time scales The tail of the outermost peak was extrapolated to evaluate decadal depth of closure.

The paper presents a study on the insufficient resilience of three coastal lake barriers at the central part of the Polish Baltic Sea coast. Environmental qualities of those lakes belonging to the NATURA2000 network dictate efforts aimed at their conservation through the maintenance of the barriers. The use of recently elaborated high resolution geological surveys demonstrated previously underestimated severe sand scarcity and indicated high threats of enhanced erosion, breaching and overtopping of the barriers. Next, the investigation of alongshore variation of nearshore wave energy dissipation, basing on the available bathymetric records and the concept of ordinary and empirical equilibrium profiles, identified potential erosion hot spots along the barriers. Finally, the XBeach model was applied to simulate the effects of rare, heavy storms with the recurrence period of 20 years with and without climate change induced sea level rise. Overall, the results demonstrated high susceptibility of the barriers to frequent fragmentation and allowed for recommendations of protection measures minimizing interference into the natural landscapes. The novelty of the paper consists in the assessment of aftermaths of extreme events by combining recent advances in coastal geology and climate change effects.

It has been demonstrated that, for the majority of beach profiles with multiple bars, the only beach parameter that controls the total nearshore wave energy dissipation, which was obtained by the integration of a constant dissipation rate in a unit water volume over Dean-type equilibrium beach profiles, is the depth at which Dean's regime is initiated. This does not depend on the Dean coefficient (A), and, therefore, the wave breaking index (y) remains the only morphodynamic parameter that controls the magnitude of that dissipation. However, A serves as a more accurate proxy of the beach state when applied with data-driven empirical beach equilibrium profiles, because it better describes the state of the seabed between the shoreline and the depth down to which the Dean concept is valid. Two exceptions to this general behavior of beaches with multiple bars have been identified: one with two zones of saturated energy dissipation, which was induced by a large offshore-most bar (which requires the introduction of the outer Dean function), and one where the bars are small and shallow, and the morphology offshore the bar zone closely resembled the equilibrium profile shape. These outliers will be discussed in detail.