Explanation

A tidal datum is a elevation used as a reference from which to a water level. Many tidal datums are calculated from a full nodal cycle (~18.6 year period) of high and low waters, others are arbitrary station defined values and some are nationally standardized elevation levels.

Definitions

The following datums will be returned for any location. They are calculated over a full nodal cycle (~18.6 years) starting at Jan 1st, 2000.

Abbreviation Expansion Description
LATLowest Astronomical TideThe lowest predicted astronomical tide.
MLLWSMean Lower Low Water SpringThe average of the lowest tide during spring tide range.
MLWSMean Low Water SpringThe average of the successive pair of lowest tides during spring tide range.
MHLWSMean Higher Low Water SpringThe average of the higher of the successive pair of lowest tides during spring tide range.
MLLWMean Lower Low WaterThe average of the lowest of the successive pair of low tides.
MLWMean Low WaterThe average of all low waters
MHLWMean Higher Low WaterThe average of the highest of the successive pair of low tides.
MLLWNMean Lower Low Water NeapsThe average of the lowest tide during neap tide range.
MLWNMean Low Water NeapsThe average of the successive pair of lowest tides during neap tide range.
MHLWNMean Higher Low Water NeapsThe average of the higher of the successive pair of lowest tides during neap tide range.
MTLMean Tide LevelThe average of all high and low tides.
MSLMean Sea LevelThe average sea level.
MLHWNMean Lower High Water NeapsThe average of the lower of the successive pair of highest tides during neap tide range.
MHWNMean High Water NeapsThe average of the successive pair of highest tides during neap tide range.
MHHWNMean Higher High Water NeapsThe average of the highest tide during neap tide range.
MLHWMean Lower High WaterThe average of the lowest of the successive pair of high tides.
MHWMean High WaterThe average of all high waters
MHHWMean Higher High WaterThe average of the highest of the successive pair of high tides.
MLHWSMean Lower High Water SpringThe average of the lower of the successive pair of highest tides during spring tide range.
MHWSMean High Water SpringThe average of the successive pair of highest tides during spring tide range.
MHHWSMean Higher High Water SpringThe average of the highest tide during spring tide range.
HATHighest Astronomical TideThe highest predicted astronomical tide.

The following datums will only be returned for U.S. tide stations:

Abbreviation Expansion Description
NAVDNorth American Vertical DatumA fixed reference for elevations determined by geodetic leveling. The datum is derived from a general adjustment of the first-order terrestrial leveling nets of the United States, Canada, and Mexico.
STNDStation DatumA fixed base elevation at a tide station to which all water level measurements are referred. The datum is unique to each station and is established at a lower elevation than the water is ever expected to reach. It is referenced to the primary bench mark at the station and is held constant regardless of changes to the water level gauge or tide staff.
The following datums will only be returned for Norwegian tide stations:

Abbreviation Expansion Description
CDChart DatumReference level for depths in navigational charts and heights in tide tables. The actual level depends on local customs.
NN1954Norway Normal Null 1954Norwegian vertical datum of 1954.
NN2000Norway Normal Null 2000Norwegian vertical datum of 2000.