Which are examples of tidal datums?

Which are examples of tidal datums?

• A. Mean Sea Level (MSL), Mean Low Water (MLW), and Mean Higher High Water (MHHW)
• B. North American Datum 1927 (NAD27) and 1983 (NAD83)
• C. Geoid
• D. Ellipsoid

Answer: (A)

Tidal datums are reference elevations derived from measurements of tides at a specific location over time, used to quantify water levels for charts and shore projects. The examples listed—Mean Sea Level, Mean Low Water, and Mean Higher High Water—are all based on tidal observations, so they fit this category. Mean Sea Level is the long-term average sea level, often used as a general height reference; Mean Low Water is the average of the low tides, and Mean Higher High Water is the average of the higher of the daily high tides. These are inherently tied to tidal cycles and vary by location.

The other options aren’t tidal datums. NAD27 and NAD83 are horizontal datums used to define geographic coordinates. The Geoid is a gravity-based surface used as a reference for vertical measurements in many leveling systems, and the Ellipsoid is the mathematical surface used for fitting coordinates to the Earth’s shape. While related to vertical and horizontal positioning, none of these are tidal datums derived from tide measurements.