Improving the Definition and Algorithms of China’s Coastline Considering the Diversity of Tidal Characteristics

Abstract

Two commonly used definitions of coastline are compared and analyzed in this article. To build a more perfect digital tide-coordinated coastline model in China, we should first solve the problems of the existing definition and unclear algorithms of China’s coastline. On the basis of defining the coastline in China as the intersection of coastal land and the mean high water spring (MHWS), it should be further revised, and defined either as an intersection of coastal land and the MHWS or as a mean higher high water level (MHHWL) considering the diversity of tidal characteristics in China Sea areas. Since MHWS is related to the extreme of the lunar phase and MHHWL is related to the extreme of the angle of the lunar declination elevation, the algorithms to obtain them are more complicated than that of mean high water (MHW) used in the United States. We should consider the specific law of tidal movement in different tide types of the predominantly semidiurnal or diurnal sea areas in China when studying the precise algorithms for MHWS and MHHWL. Several experiments show that the difference between the two types of calculations of coastal height, such as water level observations and tidal predictions, is within centimeter level. The research results of this article have a certain reference value for countries with similar coastline features as in China.

Keywords:

• Coastline
• lunar declination
• lunar phase
• MHHWL
• MHW
• MHWS
• tide

Acknowledgments

The authors would like to thank the reviewers for their valuable comments and suggestions. The authors would also like to thank the Hawaiian Sea Level Research Center in the United States for its valuable water level observations and the CST1 tidal model from China.

Additional information

Funding

This study is partly supported by the National Natural Science Foundation of China (grant nos.41706111 and 41876103).