Morphodynamic processes of the Swina gate coastal zone development (Southern baltic sea)

Abstract

Airborne photographs collected in 1938, 1951, 1973, 1996 and 2012 were used to determine the magnitude and spatial distribution of changes of 17 km-long section of the Swina Gate sandy barrier coast (southern Baltic Sea). A dune base line (DBL), beach width (BW) and width of underwater bar zone (WUBZ) were compared and their interactions were determined. Unique in terms of the Polish southern Baltic Sea coasts, during period 1938–2012 Swina Gate was dominated by accumulation, expressed mainly by strong accretion of DBL and WUBZ. Morphodynamic processes were spatially and temporally diverse, even in neighboring, morphologically homogenous areas, referred to the rate of changes which ranged from 0.3 to 3.6 m/year. Two areas of different magnitude changes were distinguished. The largest accumulation was observed in the vicinity of Swina mouth (km 428–419) while from km 419 eastwards, the changes were distinctly smaller. For the periods 1938–1951 and 1996–2012, when the magnitude of growths in the DBL is bigger than 2 m/year, a correlation between DBL changes in relation to the coastline exposure, beach width, DBL elevation and beach slope is clearly visible. The greatest growths in the DBL were noticed on the coast with: NNE orientation; beach width exceeding 60 m; DBL elevation below 1.5 m a.s.l. or exceeding 4.5 m a.s.l.; inclination below 3°. The smallest changes in the DBL, ranging from −1 to +4 m/year were observed on the coast with: NW exposure; beach width below 60 m; DBL elevation between 1.5–4.5 m a.s.l.; inclination above 3°. Noticed high temporal and spatial variations of the coastal changes and character of dune-beach-underwater bar interaction, was correlated with the number of storm events, changes of water level and wave direction and hydrological constructions placement. Results confirms their strong influence to the coast behaviour.