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Nearshore sandbar switching episodes and their relationship with coastal erosion at the Curonian Spit, Baltic Sea

Janušaitė Rasa, Jarmalavičius Darius, Pupienis Donatas, Žilinskas Gintautas, Jukna Laurynas

Oceanologia

2023

Vol. 65 (1)

71--85

The longshore realignment of nearshore sandbars is a morphodynamic phenomenon of multiple sandbar systems that has been known about for several decades. However, it is unknown how switching-related nearshore changes influence the evolution of subaerial beaches. This study aims to define the relationship between sandbar switching episodes and the dynamic state of the beach-foredune system along the Curonian Spit coast (Baltic Sea) using decadal satellite-derived and beach profiling data. To define this connection, sandbar switching locations, sandbar cross-shore positions, shoreline positions, and sand volume changes in the beach-foredune system were assessed on interannual and storm-related time scales. Twenty-seven sandbar switching episodes were observed with an average duration of 14.3 months. Most of the switching episodes occurred at preferred locations, coinciding with breaking points of different shoreline orientations where oblique waves and longshore currents prevailed. Shoreline retreat at an average rate of —14.2 m was observed within most of the sandbar switching zones. During major storm events, the average rate of erosion within the sandbar switching zones was significantly higher than the rate outside them. On an interannual time scale, a moderate average rate of erosion was observed within the sandbar switching zones compared to a small accretion rate outside them. Additional case studies of coastal evolution within the switching zones indicated well-correlated rates of switching-determined outer sandbar positions, shoreline positions, and sand volume on the beach and foredune during the switching episodes. The results of this study could be important for the identification of erosional hot spots and coastal prediction. ing by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The impact of Klaipėda Port entrance channel dredging on the dynamics of coastal zone, Lithuania

Žilinskas Gintautas, Janušaitė Rasa, Jarmalavičius Darius, Pupienis Donatas

Oceanologia

2020

No. 62 (4PA)

489--500

Dredging entrance channels to ports on open littoral drift seashores often causes major morphological changes to the shoreline. This study aims to assess the impact of dredging the Port of Klaipėda's entrance channel and the construction of the jetties on the coastal zone. Based on an analysis of cartographic material collected between 1835 and 2017, and on field data (bathymetric surveys and cross-shore profile levelling), changes to the coastal zone in the area nearest to the port were evaluated. The dominant longshore sediment transport on the Lithuanian nearshore runs from south to north. Thus, based on established patterns, intensive accretion could have been expected to take place on the southern side of the port jetties and erosion on their northern side. However, in the case of the Port of Klaipėda, in the area nearest to the port on the updrift side of the port jetties, where accretion would have been expected to take place, the nearshore depth increased throughout the 20th century (when the length and configuration of the jetties did not change). The shoreline shifted landward instead of moving further out to sea. The present study shows that the intensive dredging of the entrance channel caused nearshore and shore erosion on the updrift side of the port jetties, even while a sufficient sediment load was being transported by the longshore drift.