Trends in Tidal Levels and Mean Sea Level in the Gulf of Thailand
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Article pISSN 1738-5261 eISSN 2005-7172
Trends in Tidal Levels and Mean Sea Level in the Gulf of Thailand Nitinun Pongsiri1,2, Rhysa McNeil1,2*, and Somporn Chuai-Aree1,2 1
Faculty of Science and Technology, Prince of Songkla University, Pattani 94000, Thailand Centre of Excellence in Mathematics, Bangkok 10400, Thailand
2
Received 26 November 2019; Revised 18 May 2020; Accepted 23 August 2020 © KSO, KIOST and Springer 2020
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. Keywords − Gulf of Thailand, mean sea level, tidal constituent, tidal level, trend
1. Introduction The water levels of coastal areas are very important as their dynamics have a large impact on fisheries, marine resource management, and coastal engineering projects (Kantha and Clayson 2000). In recent years, analysis of water levels has become vital due to the huge impact climate change is having on sea-level rise. However, such an analysis is quite complex because the water levels depend on the tides, mean sea level (MSL) and non-tidal residuals. A change in any of these *Corresponding author. E-mail: [email protected]
components affects the variability of the water level (Rhein et al. 2013). While attempting to model the future dynamics of water levels, it is important to understand their historical trends and variability (Wahl and Chambers 2015, 2016). There is evidence in the literature to suggest that the trends in global extreme water levels over the last century are consistent with those of the MSL. For example, Woodworth and Blackman (2004), using global tidal datasets from 141 stations, found that interannual variations of extreme water levels were consistent with those of the MSL. Similarly, increments in extreme high waters, dating back to the 1970s, were detected by Menéndez and Woodworth (2010) based on quasi-global datas
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