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 Tidal Datums


To use the interactive map, check the "tidal Datum" box to turn on the data layer. Next zoom into an area, then click on a point. Or you can click on one of the static maps below.

Tidal datum elevations are in NAVD88 (GEOID12B). If comparing to another GEOID, e.g. the 2006 FEMA LiDAR data (based on the GEOID03 elevation model), you will need to subtract the specified LiDAR correction value to obtain the LiDAR digital elevation model elevation. For example, if the mean high water (MHW) elevation is 1.56 ft, and the LiDAR correction value is 0.10 ft, if looking for the MHW boundary in the LiDAR data set, look for a LiDAR elevation of 1.46 feet. In much of Buzzards Bay, the LiDAR correction for older GEOID models is negligible. Correction values between GEOIDs can be determined using the Vertcon Calculator.





Links

Estimation of the elevation of Mean High Water and the High Tide Line

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Updates, Explanations, and Caveats

This page is set up in 2013 to allow government officials, scientists, and engineers to find the estimated elevations of mean high water (MHW), mean low water (MHW), and the high tide line (HTL = "annual high tide" or "king tide") in the NAVD88 datum. In August 2019, we updated this page to reflect the new HTL calculations and Geoid12B data as described on our new interactive on our new Tidal Datums and the HTL for Massachusetts page. The new HTL calculations differ somehwat than that described in our 2013 QAPP. The interactive map data on this page matches our new tidal datum viewer page. When you zoom in the map, you can click individual points to see the various tidal elevations for that site. Geoide correction values should be subtracted from the tidal datums to determine equivalent LiDAR set elevations developed using a different GEOID model.

This data set was developed for our study of projected salt marsh migration with sea level rise. The Buzzards Bay NEP estimated the high tide line because it defines the regulatory boundary of salt marshes. The high tide line is equivalent to the "annual high tide" or "King Tide" for a particular year. For this analysis, we are primarily using a tidal elevation model developed by NOAA called VDatum. Using this model, we can estimate the elevation of tidal benchmarks around Buzzards Bay in the NAVD88 datum. Details of our HTL elevation calculation methodology as described on our new Tidal Datums and the HTL for Massachusetts page. You should refer to that page for more information.