Interactive Tidal Datum Viewer

On this page is an interactive map show tidal datum elevations along the coast of Massachusetts. Zoom in and click on any point and a table of elevations will pop up for that location.  The tidal datum elevations shown are mean high water (MHW), mean low water (MLW), local mean sea level (LMSL), mean tide level (MTL, average of MHW and MLW, and very close to LMSL), mean higher high water (MHHW), mean lower low water (MLLW), mean tidal range (MN), and salt marsh range (MARSH RNG), based on the formula HTL-LMSL. HTL calculated as described on Lowest marsh elevation is generally near the LMSL elevation, but may be as high in the LiDAR data set as the field MAX_LM_FT (=LMSL+MN/3).

All elevations in feet are relative to the NAVD 88 datum (zero) reference elevation. Go to our Tidal Datums of Massachusetts page for an explanation of the regulatory and ecological relevance of these elevations.  The data on this page was generated by the NOAA’s VDatum software which does not include tidal datum estimates for many embayments.  Tidal datums in these areas are generally close in elevation to the outer coast, except in very large estuaries, or near tidal freshwater rivers. VDatum is a model with estimated uncertainties. Estimates are most accurate near the coast.  Conditions within upper areas of estuaries and tidal rivers have greater uncertainties and may not be based on hydrodynamic models. For project engineering plans along the coast, elevations should be tied to local published benchmarks.

Zoom in and click on a point of interest.  The popup table will summarize the estimated tidal elevations for that location. Elevations are in feet referenced to the NAVD 88 datum. Points color coded for mean tidal range (MN). First posted June 22, 2017.  Marsh elevation range revised 28 June 2017, as per the explanation on our low marsh boundary elevation page; a denser point coverage was added 17 July 2017.