Trends in Tidal Levels and Mean Sea Level in the Gulf of Thailand

Abstract

Astronomical tides have a major impact on coastal sediment distribution, seawater levels, coastal navigation, and other coastal dynamics. Any significant change to tides could have impacts on coastal ecosystems. This study explored the hourly water level from 11 tidal gauge stations along the Gulf of Thailand over different periods using harmonic analysis. Secular trends of tidal levels, tidal range, mean sea level and tidal constituents were assessed using a linear regression model. We found changes in all the tidal levels assessed. Increasing trends were observed for almost all tidal levels and the mean sea level at all locations. At most of the locations, the trends in tidal levels were similar to the mean sea level. Widespread increasing trends were observed in relation to the tidal levels, and in most cases, the trends were consistent with the mean sea level. Analysis of the tidal harmonic constituents showed significant trends for the luni-solar diurnal constituent (K1) at most stations. However, the magnitude of the trends in the harmonic constituents was less pronounced compared to the trends in water levels. Coastal management policies should take into account these widespread changes in tides.