# Analysis of the Accessibility of the Swinoujscie-Szczecin Fairway for Deep-Draught Ships
## 2 Study Area
### Hydrological Characteristics
#### 2.1.1 Water Levels in the Fairway  
Changes in water levels change the water reserve under the keel of a ship [23,24]. This causes a change in sailing conditions (different manoeuvring properties of the ship, change in settlement). There may be various reasons for the change in water levels. There are no tidal movements in the Oder-Szczecin Lagoon-Baltic Sea system. Tidal changes in the Baltic are too small to cause significant tidal movements throughout the system. Instead, significant changes in water levels are observed, which are to be attributed to the influence of the wind and the piling up and pushing away of water by the wind. Northerly winds pile up water from the seaward side towards the coast, also pushing water on the leeward side of the Szczecin Lagoon. As a result, significant currents appear in the estuaries. Swinoujscie  
The mean sea level in Swinoujscie, calculated on the basis of measurements carried out between 1811 and 1985, was 491.1 cm \(\pm\) 0.3 cm [25]. Over the same period, a gradual rise in sea level was observed, which was estimated at 0.7 mm per year \(\pm\) 0.1 mm [26]. A similar upward trend was also recorded at other locations along the Polish Baltic coast, from 1.1 mm per year in Kolobrzeg to 1.2 mm per year in Gdansk Nowy Port. Data from subsequent decades shows that the rate of sea level rise increased to about 4.2 mm per year between 1971 and 1990 [27]. Analysing the thirty-year period 1961-1990, the average sea level in Swinoujscie was 499.0 cm. Both mean and extreme values recorded during this period were related to the NAP (Normaal Amsterdams Peil) zero level in Amsterdam. In the period 2008-2022, the average sea level in Swinoujscie was 506.5 cm (the study was conducted on the basis of IMGW data), which confirms the observed upward trend. Compared to earlier decades, the values are higher--for the period 1961-1990 the average sea level was 499.0 cm, while for the period 1811-1985 it was estimated at 491.1 cm. The variability of the water level between 2008 and 2022 was significant, ranging from a minimum value of 374.0 cm to a maximum value reaching 640.0 cm, indicating periodic rises associated with dynamic meteorological phenomena. The increase in mean sea level is consistent with previous studies, according to which, in the second half of the 20 th century, the rate of Baltic Sea level rise in Swinoujscie was about 4.2 mm/year. Strong currents in the estuaries overpower the normal, moderate water flow in the system, which, apart from the outflow of river water, is regulated by a difference between the density of the fresh water of the Szczecin Lagoon and the seawater of the Baltic Sea. In addition, the flow in the Lagoon is subject to the influence of strong winds above the water surface, causing local rise and fall of the water level and consequently recirculation of water. During strong winds the flow in the Szczecinski Lagoon is largely three-dimensional, where surface currents and bottom currents can strongly oppose each other. As the data on extreme water levels is derived from measurements, it can be considered to include all natural phenomena that could potentially affect changes in hydrostatic pressure levels. Complementing the issue of water levels, differences in water levels are also important in the Kiel Canal and the Piast Canal, as they contribute to strong currents in both canals. The verification of water levels in the port of Swinoujscie was also carried out based on IMGW data for the period 2008-2022. Similar methods of multi-source remote sensing, including radar altimetry and optical imagery, have been successfully used to monitor long-term water level changes in wetlands. [PERSON] et al. [28] demonstrated that integrated satellite-based observations can accurately detect hydrological fluctuations even in remote or data-sparse regions, supporting adaptive water management under changing environmental and climatic pressures.