The National Oceanic and Atmospheric Administration, National Ocean Service, Center for Operational Oceanographic Products and Services (CO-OPS) has updated the nation's tidal datums to NTDE 83-01.

To access the CO-OPS website visit:

NTDE is a specific 19-year period over which tide observations are taken to determine Mean Sea Level and other tidal datums such as Mean Low Water and Mean High Water. The current update defines the 19-year period as 1983-2001. A tidal datum is a vertical reference based on a specific stage of tide that serves as a baseline elevation to which sounding depths or topographic heights are referenced. The 19-year period includes an 18.6 year astronomical cycle that accounts for all significant variations in the moon and sun that cause slowly varying changes in the range of tide. NTDE 83-01 is adopted to assure that tidal datum determinations throughout the United States will be based on one specific common reference period.

The State of Florida, Department of Environmental Protection, Division of State Lands, Bureau of Surveying and Mapping (BSM) working in conjunction with CO-OPS continue to process tidal datums on NTDE 83-01 and shown on the BSM Land Boundary Information System (LABINS) website. Mean High Water Surveys or studies are based on NTDE 83-01 and referenced to North American Vertical Datum adjustment of 1988 (NAVD88) with the unit of measurement being in feet. Professional Surveyors and Mappers may continue to establish tidal datums referenced to local tidal datum (LTD) if impractical to reference tidal datums to NAVD88.

For further general information about the update, please contact:
Steve Gill at 301-713-2981 Extension 139, or

For specific information about the tidal datum to be used at your location, please contact:
Lamar Evers at 850-245-2606 or