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Tidal Datum Description

Mean Low Tide (MLT)

MLT was established by United States Army Corps of Engineers (USACE) back in the 1930s. The USACE MLT datum only exists on benchmarks they established along the Intracoastal Waterway back in the 1930s. To connect these benchmarks to TCOON stations would be expensive and not particularly useful. Galveston USACE now use TCOON's Mean Lower Water (MLW) values as computed by NOAA's National Ocean Service (NOS).

For More Information

• NOAA's website has a comprehensive description of tidal and geodetic datums.
• Tidal definitions document from the Florida Department of Environmental Protection (8K PDF).
• NOAA's NOS Tide and Current Glossary (600K PDF).
• "Understanding Tides" by Steacy Dopp Hicks (2MB PDF).

Navigating the DNR Tidal Datum page

Tidal Datum Schematic

Station Datum

Station Datum

All water elevations are measured at each station relative to the Station Datum. Station Datum is an arbitrary zero point set low enough at each station such that the water level will never be below this point. The arbitrary number is designed to allow all water level observations to be positive numbers. Each station has its own unique Station Datum because of physical conditions at the station.

A series of deep-driven-rod bench marks exist to maintain the station's zero point over time. If any of the benchmarks or the tide gage itself were to move, the water level measurements associated with that benchmark or tide gage could be adjusted accordingly to coincide with the readings of the others which did not move. In the figure below, station datum is labeled "STND" and is located at the bottom of the figure.