03-13190. Notice of Change to the Nation's Tidal Datums With the Adoption of a New National Tidal Datum Epoch Period of 1983 through 2001

AGENCY:

National Ocean Service (NOS), National Oceanic and Atmospheric Administration (NOAA), Department of Commerce (DOC).

ACTION:

Notice to advise the public of national updates to tidal datums due to the adoption of a new National Tidal Datum Epoch 1983 through 2001.

SUMMARY:

NOAA's National Ocean Service, Center for Operational Oceanographic Products and Services (CO-OPS), will update the Nation's tidal datums to a new National Tidal Datum Epoch (NTDE) to adjust for changes in mean sea level that have occurred along the Nation's coast over the past 25 years. The NTDE update from the 1960-1978 to the 1983-2001 time period will be effective April 21, 2003. The 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 period includes an 18.6 year astronomical cycle that accounts for all significant variations in the distances to the moon and sun that cause slowly varying changes in the range of tide. It is the policy of NOS to consider a revised NTDE every 20-25 years in order to take into account relative sea level changes caused by global sea level rise and the effects of long term land movement on local sea level due to subsidence or glacial rebound. The NTDE of 1983-2001 has been adopted so that all tidal datums throughout the United States will be based on one specific common reference period.

This action is necessary to provide the latest up-to-date information available for applications that are essential to supporting Federal, State and private sector coastal zone activities, including hydrographic surveys and coastal mapping, navigational safety, wetland restoration, marine boundary determinations, coastal engineering, storm warnings and hazard mitigation, emergency management, and hydrodynamic modeling.

FOR FURTHER INFORMATION:

Visit the NOS' CO-OPS Web site (http://www.tidesandcurrents.noaa.gov) or contact the CO-OPS office at the following address: NOAA, National Ocean Service, CO-OPS, Products and Services N/OPS3, Attn: Water Levels, 1305 East-West Highway, Silver Spring, MD 20910-32821, U.S.A., Telephone: [phone] x176, Fax: [phone].

SUPPLEMENTARY INFORMATION:

Due to the small vertical changes (0.10 meters/0.3 foot or less) in comparison to the overall accuracy of hydrographic-cartographic processes and scale of the charts, for the most part, the shoreline, depth soundings values, isobaths, etc., will not be significantly modified as a result of the tidal datum updates. However, in some regions that have experienced rapid land movement, changes to actual soundings and shoreline depiction may be required on the next regularly scheduled chart edition. Although depictions of the datum changes will not be evident on the largest scale NOS nautical charts, the datum changes will be noticeable when establishing or re-occupying tide stations using accepted surveying techniques and the numerical relationships for tidal benchmarks provided by NOS' CO-OPS. These tidal datum relationships will be made available to the public in the form of updated published tidal benchmark sheets and accepted datums.

Dated: May 21, 2003.

Jamison S. Hawkins,

Acting Assistant Administrator, Ocean Services and Coastal Zone Management, National Oceanic and Atmospheric Administration.