Współczesna dynamika plaż i wydm w środkowej części Mierzei Wiślanej oraz prognoza ich zmian po wykonaniu falochronów kanału = Contemporary dynamics of the beaches and dunes in the central part of the Vistula Sandbar, as well as forecast changes following the construction of canal breakwaters

The aim of the work described here has been to analyse contemporary changes along the shore along the central part of the Vistula Sandbar located on the Baltic’s south coast. There, breakwaters are being installed to protect the canal cut that has been under construction since 2020 (fig.1). Shoreline changes involving both dunes and beaches have been predicted to arise following construction of breakwaters, which will obviously influence the dynamics of the previously natural shore of the Sandbar. Factors exerting done in the 2003‑2020 period. The section of the Sandbar under discussion (the middle part, at km 18‑25, fig. 1, 2) has so far shown only limited accumulation trends. Plate 1 presents different relief of the foredunes caused by storm surges and aeolian processes. The wind regime for 2001‑2017 features the more marked presence of wind from the W and SW sector. Aeolian accumulation caused by such westerly winds is rebuilding the beach and dune in the investigated area (fig. 6‑8). The strongest winds are those from the NW that arise during the autumn-winter period. The orientation of the sandbar coast ensures that erosion in the course of storm surges is different. The middle part of the Vistula Sandbar is only eroded during the highest storm surges (fig. 3). Over the research period, it was possible to observe erosion of various types caused by storm surges recorded in Gdańsk. Since 2003, there have been several storm surges featuring a water level higher than 1.2 m AMSL. Each such surge ensures severe erosion of dunes (as in 2004, 20006, 2007, 2012, 2017 and 2019). Storm erosion is a major factor in dune development: the higher the surge, the higher the levels of water run up and coastal erosion (fig. 4). During the highest surges (featuring water of H>1.2 m AMSL, the run-up is of almost 4 m AMSL. The mean rate of retreat at the base of the foredune is 3‑4 m, while the maximum reaches 7‑8 m. In the periods between storms, the areas at the bases of dunes increases by 0.8 to 1.5 m/y. Reconstruction of the dunes took place up to 2‑3 years after a major storm surge. The sand building foredunes is fine and medium (average 0.20‑0.21 mm). There are fines sands along the whole Vistula Sandbar, while beach dune sand is coarser. The coarsest sand is the type that builds the beach ridge (0.3‑0.4 mm). This type of material comes from the cliffs of the Sambian Peninsula located in the NE part of the Gulf of Gdańsk. Plants scattered across the beach ensure aeol