# Analysis of the Accessibility of the Swinoujscie-Szczecin Fairway for Deep-Draught Ships
## 2 Study Area
### Impacts of Water Levels on Navigation  
The study area therefore encompasses the entire Swinoujscie- Szczecin fairway, whose hydrological conditions are strongly influenced by water level fluctuations and meteorological conditions. This is one of the most important waterways in Poland; therefore, a thorough understanding of the influence of water levels on ship traffic and draught is crucial to optimise maritime traffic and ensure the safety of shipping in this region. Similar navigational challenges related to water level variability and under-keel clearance management are observed in other major European waterways. For example, the Kiel Canal (Nord-Ostsee-Kanal) [30,31], which connects the North Sea and the Baltic Sea, experiences restricted depths and requires precise UKC management due to the volume of commercial traffic and narrow channel geometry. Similarly, the Elbe River [32] near Hamburg is affected by tidal dynamics, sedimentation, and draught restrictions, requiring constant monitoring and fairway maintenance. These examples show that managing the accessibility of fairways under variable water levels is a challenge for many important waterways. They indicate that hydrological analysis plays a significant role in navigational decision-making. Reserve of Water Under the Keel of \"Maximum Vessels\" Passing the Upgraded Swinoujscie-Szczecin Fairway  
The permissible draught of \"maximum vessels\" passing the modernised Swinoujscie-Szczecin fairway has been determined taking into account the operation of the dynamic system for determining the under the keel clearance. Complementary approaches for relating hydrological data to navigational constraints have been explored in large inland water bodies such as Dongting Lake. [PERSON] et al. [28] developed machine learning and polynomial regression models to predict water surface area based on historical water levels, demonstrating high reliability in hydrodynamic analysis over decades. Such coupling models may offer further utility in dynamic fairway access assessments, especially under evolving hydro-climatic conditions. Analysing the individual components of the under the keel clearance on the Swinoujscie-Szczecin waterway, it can be concluded that the highest values are reached by the following components:  
* a reserve for lowering the water level due to fluctuations in the water table level in relation to the map zero (taken as \(\Delta\hbar\), which is the permissible lowering of the water table level);
* settling allowance for the ship in motion depending on the ship's speed and draught and fairway parameters. The reserve for water level reduction represents the permissible drop in water level (\(\Delta\)h) at which a \"maximum vessel\" of a given type may safely pass through the Swinoujscie-Szczecin fairway, without violating the required under-keel clearance (UKC). In this context, UKC is defined as the minimum vertical distance between the ship's heel and the seabed, ensuring that the vessel does not touch the bottom even during motion or squat. It is a safety margin that depends on vessel speed, squat, waves, heeling, and water level fluctuations. The permissible draught (T) of a vessel on a fairway with a given depth (D) and under current water level conditions (h(t)) is governed by the inequality:  
\[\text{h(t)}\geq\text{hkr(T)}=\text{h}_{0}-\text{(D-T+\Delta\text{h})}\]  
where \(h_{0}\) is the reference water level (assumed as 500 cm), and \(\Delta\)h is the allowable water level drop, ensuring the required UKC is maintained. If the actual water level drop at any given time, \(\Delta\)h(t), exceeds this permissible value:  
\[\Delta\text{h(t)}>\Delta\text{h}\]  
The vessel must wait before entering the fairway until the water level rises to within the acceptable threshold:  
\[\Delta\text{h(t)}\leq\Delta\text{h}\]  
This condition defines the fairway's availability for deep-draught ships and affects traffic planning. The value of \(\Delta\)h is chosen depending on the vessel type and its operational flexibility.