NOTICE
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(Portions of the following statement are excerpted from NOAA/NOS/CO-OPS Web Site)
The National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS) is updating the nation's tidal datums to a new National Tidal Datum Epoch (NTDE) to reflect changes in mean sea level along the nation's coast. To access the NOAA/NOS website click HERE. |  |
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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 Lower Low Water and Mean High Water. This latest update will define 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. The NTDE has been adopted so 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, Bureau of Surveying and Mapping (BSM) working in conjunction with The NOS Center for Operational Oceanographic Products and Services (CO-OPS) are in the process of changing tidal datums in Florida to be based on the 1983-2001 NTDE. This information will be added to BSM's Land Boundary Information System (LABINS) website as the Tidal Benchmark Sheets are updated by NOS. A complete update on all of the Tidal Benchmark Sheets will take a couple of years. If the new information is available on LABINS, it can be used. In the interim, if the new epoch data is not available on LABINS at a given tide station or data point, the user should continue to use the old 1960-1978 tidal datum epoch data. Future mean high water surveys or studies using the old 1960-1978 tidal datum epoch will continue to be based on the National Geodetic Vertical Datum (NGVD) of 1929 with the unit of measurement being in feet. Mean high water surveys using the 1983-2001 NTDE will be based on the North American Vertical Datum (NAVD) of 1988 and the unit of measurement will be in meters. Study sites where benchmarks are not available based on the NGVD of 1929 or NAVD of 1988 the surveyor can still establish an assumed (local) vertical datum.
For further data, delivery schedules and general information about the update, please contact:
Steve Gill at 301-713-2981 Extension 139, or Stephen.Gill@noaa.gov
For further specific information about the tidal datum to be used at your location, please contact:
Lamar Evers at 850-245-2606 or Lamar.Evers@dep.state.fl.us