Notice of Change to the Nation's Tidal Datums With the Adoption of a Modified Procedure for Computation of Tidal Datums in Area of Anomalous Sea-Level Change

Zusammenfassung

NOAA has typically updated tidal datum elevations for the nation to new National Tidal Datum Epoch (NTDE) time periods every 20- 25 years. Updates are necessary due to long-term sea level change. In 1998, NOS recognized the need for a modified procedure for determination of tidal datums for regions with anomalously high rates of relative sea level change. This modified procedure is necessary at selected stations to ensure that the tidal datums accurately represent the existing stand of sea level. The procedure is limited only to those stations in areas with high rates of vertical land motion that have documented anomalous relative sea level trends exceeding 9.0 millimeters per year. Sea level analyses in these anomalous regions are conducted approximately every 5 years to determine if the mean sea level difference exceeds the established threshold tolerances in order to qualify for a special update. Anomalous relative sea level trends are seen along the western Gulf Coast, southeast Alaska, and southern Cook Inlet, AK. For example, the magnitude of the sea level trends in these areas is +9.24 millimeters per year in Grand Isle, LA; -12.92 millimeters per year in Juneau, AK; and -9.