# 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
The mean and extreme values of the water level are shown in Figure 3, while the frequencies of occurrence of individual water levels are presented in Figure 4--this shows a histogram of the water level over the period in question with a fitted normal distribution curve. As can be seen, the distribution of water levels in this period is close to a normal distribution and extreme water levels occur very rarely. Between 2008 and 2022, the water level in Swinoujscie fluctuated between 374 and 640 cm. Figure 5 presents the empirical distribution and its inverse. This graph allows assessing the probability of occurrence of particular water levels during the study period. The graph shows that approximately 50% of the observations were below the mean value of the water level (506.5 cm). Figure 4: Frequency of water levels in Swinoujscie 2008–2022. Blue columns represent the empirical distribution of water levels, and the blue line shows the fitted normal distribution. Figure 3: Extreme and mean values of water levels for Swinoujscie [cm]. Mean sea level: 500 cm. Figure 6 shows the cumulative empirical water level distribution (ECDF) for Swinoujsicie. This curve illustrates the probability with which the water level does not exceed a certain value. Analysis of the graph indicates that the distribution of water levels shows a typical sigmoidal shape, suggesting a dominance of values close to the mean water level and a relatively low incidence of extreme values. Table 2 shows the frequency and average duration of water levels below mean sea level in Swinoujsicie from 2008 to 2022 by \(\Delta\)D. As the amplitude of water levels increased, the frequency of their occurrence decreased (from 188 occurrences for a decrease of 10 cm to 5.8 for a decrease of 60 cm) as well as their duration (from 13 h for a decrease of 10 cm to 5.6 h for a decrease of 60 cm). Figure 5: Empirical distribution and inverse empirical distribution water levels in years 2008–2022 in Swinoujsic. Figure 6: Cumulative relative frequency of occurrence of particular water levels in Swinoujsicie in the years 2011–2019. Figure 8: Histogram of the occurrence of water levels in the Thinning River between 2008 and 2022. Blue columns represent the empirical distribution of water levels, and the blue line shows the fitted normal distribution. Figure 10: Cumulative relative frequency of water levels in Trzebiez from 2008 to 2022. \begin{table}
\begin{tabular}{c c c} \hline  & \multicolumn{2}{c}{**Trzebiez**} \\ \hline \multicolumn{3}{c}{**Water Level Drops Below the Mean Level in 2008–2022**} \\ \hline
**Delta “D” [cm]** & \multicolumn{2}{c}{**Average Annual Number of Occurrences**} & \multicolumn{2}{c}{**Average Duration of Water Level Drops [h]**} \\ \hline
30 & 23.47 & 15.89 \\ \hline
40 & 10 & 12.24 \\ \hline
50 & 2.4 & 10.19 \\ \hline
60 & 0.33 & 20.4 \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._  
Figure 9: Empirical and inverse empirical distributions of water levels in Trzebiez from 2008 to 2022. Szczecin Most Dlugi  
The study was also carried out for the measurement point in Szczecin (located in the vicinity of the Dlugi Bridge). Similarly to the previous measurement points, the minimum, average, and maximum water levels in Szczecin were examined (Figure 11). The average water level was 517.8 cm, the minimum water level was 426 cm, and the maximum level reached 635.3 cm, which indicates sporadic but extreme changes in water level during this period. The frequency of occurrence of particular water levels in the Szczecin area is shown in Figure 12. The probability of occurrence of particular water levels is shown in Figures 13 and 14. Figure 11: Minimum, average, and maximum water levels in Szczecin 2008–2022. Figure 12: Frequency of water levels in Szczecin 2008–2022. Figure 13: Empirical distribution and inverse empirical distribution in Szczecin. Table 4 shows the frequency and duration of occurrence of water levels lower than the mean water level by 10, 20, 30, 40, 50, and 60 cm.