1. Brief History of North American Vertical Datums Mean Sea Level Datum 1900 United States Lake Survey 1903 *Mean Sea Level Datum 1929 United States Lake Survey 1935 International Great Lakes Datum 1955 *National Geodetic Vertical Datum 1929 **International Great Lakes Datum 1985 **North American Vertical Datum 1988
2. Early vertical datums were established for charting & hydrographic surveys of harbors along the eastern seaboard of the U.S.
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5. Adjustments to North American vertical datum based on increased tidal observations Year of Adjustment Kilometers of Leveling Number of Tide Stations 1900 1903 1907 1912 1929 21,095 31,789 38,359 46,468 75,159 (U.S.) 31,565 (Canada) 5 8 8 9 21 (U.S.) 5 (Canada)
15. Mixed Tide at Pass Cavallo – May 23 rd to 24 th , 2005
16. Mean Sea Level Trend – Galveston Gauge 8771450 - Galveston Pier 21 mean sea level trend is ~ + 6.5 mm – per year ( 2.13 feet per century) Mean Sea Level Data from 1908 to 1999