Measurements of long waves in port of Klaipėda, Lithuania

Port of Klaipėda is in Klaipėda Strait that connects the Curonian Lagoon with the south-eastern Baltic Sea. Its quays are well sheltered from open sea waves but the port area still hosts dangerous water level oscillations that are apparently generated in the system consisting of the Curonian Lagoon and a strait that connects the lagoon with the Baltic Sea proper. The analysis of spectral composition of these oscillations is based on continuous pressure recordings with a frequency of 4 Hz in Port of Klaipėda during the stormy season December 2016–January 2017. The majority of the energy of oscillations is concentrated in three frequencies bands. Considerable water level changes occurred owing to infragravity motions with periods >30 s (<0.03 Hz) and disturbances with the typical periods of wind waves at the Lithuanian coast with periods of 3–10 s (0.1–0.3 Hz). The highest peak in the wind wave frequency band corresponds to typical storm conditions in the Baltic Sea with periods 9–5 s. While the typical amplitudes of oscillations in this range were modest, particularly hazardous changes in the water level, with amplitudes >0.5 m, were created at lower frequencies. The recording reveals the presence of harbor oscillations with periods 30–200 s (0.005–0.03 Hz) and seiches of the Curonian Lagoon with periods >1200 s (<0.0008 Hz).