What are tidal datums?
A tidal datum is a surface defined by a particular phase of the tide. Examples of tidal datums are Mean Higher High Water (MHHW), Mean Tide Level (MTL), Mean Sea Level, and Mean Lower Low Water (MLLW). Tidal datums are computed using observations acquired at a specific tide station and are valid only at that particular station. A datum located in a water body is considered tidal if the variation in water level is sufficiently predictable based upon the phases of the moon and sun. Otherwise, it is considered a non-tidal datum. Back to top 6. What is a tidal epoch? Tidal variations can be considered as comprised of periodic and apparent secular trends. A specific 19-year period based upon the Metonic cycle is selected so that all tidal datum determinations will have a common reference period. This period is termed a tidal epoch. For tide stations located in the United States and its possessions, this period is called the National Tidal Datum Epoch (NTDE). The present NTDE is the period 1
