This document discusses the history of vertical datums in North America, including Mean Sea Level Datum 1900, U.S. Lake Survey Datums of 1903 and 1935, NGVD 1929, and NAVD 1988. It describes how early datums were based on tide gauge measurements but have shifted over time due to crustal movement and rising sea levels. NAVD 1988 was established using a single tide gauge in Quebec and gravity measurements to define a stable reference surface not dependent on sea level.

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.

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)

7. Typical Tide Gauge Diagram

8. Tide Gauge Recorder – circa 1925

9. Typical Modern Tide Gauge Station Diagram

10. Tide Gauge – Anchorage, Alaska - 1913

12. Basic Tide Phases & Cycles

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

17. Change in Global Mean Sea Level

22. NGVD-29 to NAVD-88 Differences

23. NGVD-29 to NAVD-88 Height Differences units in centimeters

24. KP0037 DESIGNATION - A 42 KP0037 PID - KP0037 KP0037 STATE/COUNTY- NV/WHITE PINE KP0037 USGS QUAD - HOGUM (1987) KP0037 KP0037 *CURRENT SURVEY CONTROL KP0037 ___________________________________________________________________ KP0037* NAD 83(1986)- 39 04 07. (N) 114 27 07. (W) SCALED KP0037* NAVD 88 - 1747.784 (meters) 5734.19 (feet) ADJUSTED KP0037 ___________________________________________________________________ KP0037 GEOID HEIGHT- -20.69 (meters) GEOID03 KP0037 DYNAMIC HT - 1745.927 (meters) 5728.10 (feet) COMP KP0037 MODELED GRAV- 979,504.0 (mgal) NAVD 88 KP0037 KP0037 VERT ORDER - FIRST CLASS II KP0037.The orthometric height was determined by differential leveling KP0037.and adjusted by the National Geodetic Survey in June 1991. KP0037 KP0037.The geoid height was determined by GEOID03. KP0037 KP0037.The modeled gravity was interpolated from observed gravity values. KP0037 SUPERSEDED SURVEY CONTROL KP0037 NGVD 29 (??/??/92) 1746.576 (m) 5730.22 (f) ADJ UNCH 1 2 KP0037 KP0037.Superseded values are not recommended for survey control.

25. Gravitational Effects on Leveling – Distortions in the NGVD-29 network Leveled Height Differences B A C Topography

26. Transferring the elevation from a tide gauge to nearby benchmarks – Alaska - 1915

27. Leveling crew - Navajo Springs, Arizona - 1921

28. Benchmark crew - Utah, 1934

29. Leveling crew - rural Mississippi - 1935

30. Leveling crew – Whisky Pass, Colorado - 1931

31. Leveling crew – Salmon River, Idaho - 1945

32. Extending the Network – NGVD- 29 – Vertical control in the United States as of 1936