Baltic Sea datums and their unification as a basis for coastal and seabed studies

This paper presents examples of application of a common reference datum, such as NAP, within the elevation EVRS reference system for the Baltic Sea. A common reference datum allowed for setting the geographical pattern of occurrence of extreme sea levels in the Baltic Sea. The eastern Baltic coasts exposed to western air masses are vulnerable to extreme hydrological events (the Gulf of Finland, the Gulf of Riga and the Gulf of Bothnia). On the contrary, the Swedish coasts of the central and northern Baltic are the least threatened by extreme sea levels. The south-western coasts of the Baltic Sea (the Bay of Mecklenburg and the Bay of Kiel) cover the basins with the most frequent and the most severe storm falls and extremely low sea levels. Demonstration of the Baltic surface deformation magnitude during a storm event is another example of NAP application. The instantaneous height difference between the north-eastern and south-western coasts was 356 cm, which resulted from the negative impact of pressure (water cushion) induced by a dynamic and deep low-pressure system moving through the Baltic Sea. The common reference datum allowed for visualization of the so-called “theoretical water” distribution which has a wide application in the hydraulic engineering within the coastal zone. In addition, the study provides examples of differences that may be observed during storm events between the real sea-level data and the hydrodynamic model forecast. This is of great practical significance in terms of forecasting storm surges in the Baltic Sea.