Fundamentals of Surveying (FS) Practice Exam

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

1. 10 years

2. 15 years

3. 19 years

4. 25 years

The correct answer is: 19 years

The principal tidal datums in the United States are determined based on a 19-year period. This duration is significant as it encompasses a full cycle of the moon's phases and their gravitational influence on the Earth's tides. The 19-year cycle, known as the Metonic cycle, is key to understanding and predicting tidal patterns because it captures a range of astronomical variations, ensuring that the calculated datums reflect the regular and predictable shifts in tidal behavior over time. Using a 19-year period allows for the smoothing out of anomalies that may arise in shorter time frames, providing a more stable and accurate representation of tidal patterns for nautical charts, engineering projects, and coastal management. This period captures enough data to account for variations caused by changes in the Earth’s orbit and axial tilt, making it the standard timeframe for establishing reliable tidal datums across the United States.