What is the standard period used to determine principal tidal datums in the US?

The standard period used to determine principal tidal datums in the United States is 19 years. This period corresponds to the Metonic cycle, which is a lunar cycle that repeats approximately every 19 years. During this time frame, the positions of the moon and the sun relative to the Earth return to nearly the same state, affecting the tidal patterns and ensuring that the tidal data collected can adequately represent the cyclical nature of tides.

Using a 19-year period allows for a comprehensive analysis of tidal fluctuations and extremes, ensuring that tidal datums such as mean sea level, mean high water, and mean low water are determined from sufficient data that accurately reflects all the variations in tides that occur over this extended time frame. This long-term approach captures the influences of seasonal changes, weather patterns, and potential climate variations that might impact tidal behaviors.

Other time periods suggested do not align with the established practices for tidal analysis in the U.S.; hence they are not used for determining these principal tidal datums.