Determination of Tidal Datums and Tide Characterization and Prediction in Cyprus via the PYTHEAS National Tide Gauge Network

Tide gauges remain the fundamental instrument for the determination of the absolute sea level and its variation over time. Following the establishment of the PYTHEAS national tide gauge network, which consists of five tide gauge stations located in strategic positions along the coastline of the government-controlled areas of the Republic of Cyprus, sea level observations were collected and analyzed. The main objective of this research is the determination, for the first time, of the most important tidal datums to support hydrographic surveying activities and promote critical environmental studies, such coastal erosion. Through the analysis of the data the following tidal datums were determined: Mean Sea Level (MSL), Mean Tide Level (MTL), Mean High Water (MHW), Mean Higher High Water (MHHW), Mean Low Water (MLW), Higher High Water (HHW) and Lower Low Water (LLW). These datums were estimated from sea level observations collected over the time span between January 2018 to April 2022. The dataset underwent through a complete quality control procedure, which was designed according to the latest international standards and included, among others, the influence of the tide gauge stability and the barometric pressure on the time series, and the detection and elimination of outliers. Furthermore, a thorough harmonic analysis was carried out, by means of the Harmonic Analysis Method of Least Squares (HAMELS), on the sea level observation dataset to highlight the effect periodic motions of the Earth, Sun and Moon have on local tide. In the context of this research, a total number of 68 tidal constituents were identified. Moreover, by using the Doodson X0 filter, the astronomical impact on the sea level was estimated by separating the astronomical influence component from the meteorological residuals. Data processing and analysis were carried out using custom in-house developed software. Finally, the estimated mathematical values of the tidal constituents, each of which describe a specific cosine curve, were utilized to calculate a tidal prediction up to December 2026.