# Analysis of the Accessibility of the Swinoujscie-Szczecin Fairway for Deep-Draught Ships
## 2 Study Area
### Impacts of Water Levels on Navigation
Two types of vessels are distinguished:  
* vessels that should not experience delays, such as container ships and other liner services. For these, a higher safety reserve \(\Delta\)h is assumed;
* vessels for which waiting is acceptable, such as bulk carriers, tankers, and tramp shipping. For these, a lower \(\Delta\)h value may be selected, depending on the acceptable average waiting time. The expected number of waiting events per year for vessels with maximum draught is determined based on two parameters:  
\(n_{r}\)--average number of annual occurrences when water levels drop below the critical level; \(t_{r}\)--average duration of such events [h]. Assuming a uniform distribution of water level drops throughout the year and the frequency of surveyed vessels entering the port, it is possible to determine the probable number of expectations per year of vessels with maximum draught for the permitted water level:  
\[P_{\Delta h}=\frac{I_{i}\cdot n_{r}\cdot t_{r}}{G_{r}}\big{[}year^{-1}\big{]}\]  
where: \(P_{\Delta h}\)--probable number of maximum draught vessels expected per year for the permitted water level [year\({}^{-1}\)]; \(I_{r}\)--annual frequency of entries of \"maximum vessels\" (having maximum draught) [role\({}^{-1}\)]; \(n_{r}\)--annual average number of occurrences of water levels below the admissible level; \(t_{r}\)--average duration of water levels below the admissible level [h]; \(G_{r}\)--number of hours per year (8760 h). Based on the results of verification studies of water levels in the Swinoujscie-Szczecin fairway in the years 2011-2019, the following was determined:  
* average annual number of occurrences of water levels lower than 465 cm, 470 cm, or 475 cm, respectively;average durations of water levels lower than 465 cm, 470 cm, or 475 cm, respectively. The expected number of vessel arrivals was determined based on forecasted port traffic data and operational profiles of ships calling at the ports of Szczecin, Police, and Skolwin. Two distinct categories of maritime traffic are considered:  
* Liner vessels (e.g., container ships), which operate on fixed schedules and for which waiting time at the fairway is generally not acceptable. For these vessels, a more conservative under-keel clearance and higher water level reserve \(\Delta\)h is applied to minimize disruptions;
* Tramp vessels (e.g., bulk carriers, tankers, LPG carriers), which operate flexibly and may be allowed to wait for favourable conditions. In this case, \(\Delta\)h may be optimized based on acceptable waiting time thresholds. In this study, the annual number of arrivals of \"maximum vessels\" for which waiting is operationally acceptable was assumed to be 100 per year (Ir = 100 [year\({}^{-1}\)]). This value reflects the projected frequency of deep-draught vessels that may be affected by temporary water level reductions and is used in the calculation of expected waiting events (P\(\Delta\)h). The assumptions are aligned with historical traffic data and development plans for bulk and liquid cargo terminals in the Port of Szczecin region. The probable number of waiting times of these vessels with maximum draught for the permissible water level was determined for 465 cm, 470 cm, and 475 cm, respectively (Table 5).