NGVD29 vs NAVD88
Reviewed • Standard Hydrology Definition • WaterLakeLevel
# NGVD29 vs NAVD88
In the United States, water elevations are tied to two primary geodetic vertical datums:
The historical vertical control network based on mean sea level computed across 26 tide stations in the US and Canada. Most major dams built between 1930 and 1975 have their authorized full pool elevations legally defined in NGVD29.
The modern, satellite-refined geodetic datum that accounts for gravitational anomalies, continental crust shifting, and tectonic movement.
Depending on geographic location in the US, NAVD88 can be anywhere from 0.5 feet to over 2.0 feet higher or lower than NGVD29 at the exact same lake! When measuring dock or seawall clearance, you must ensure your survey benchmark and the lake gauge share the exact same datum.
The difference between the historical 1929 vertical datum and the modern 1988 North American geodetic datum.
NGVD29 vs. NAVD88 Explained
In the United States, water elevations are tied to two primary geodetic vertical datums:
NGVD29 (National Geodetic Vertical Datum of 1929)
The historical vertical control network based on mean sea level computed across 26 tide stations in the US and Canada. Most major dams built between 1930 and 1975 have their authorized full pool elevations legally defined in NGVD29.
NAVD88 (North American Vertical Datum of 1988)
The modern, satellite-refined geodetic datum that accounts for gravitational anomalies, continental crust shifting, and tectonic movement.
The Datum Shift Warning
Depending on geographic location in the US, NAVD88 can be anywhere from 0.5 feet to over 2.0 feet higher or lower than NGVD29 at the exact same lake! When measuring dock or seawall clearance, you must ensure your survey benchmark and the lake gauge share the exact same datum.
Explore Other Hydrology & Boating Terms
Acre-Foot
A volumetric water unit representing the amount of water required to cover one acre of land to a depth of one foot.
Conservation Pool
The volume of water stored in a reservoir dedicated to beneficial uses such as drinking water, power, and recreation.
Datum
A reference surface or mathematical baseline from which vertical elevations or geographic coordinates are reckoned.
Dead Pool
The critical low-water elevation below which water cannot flow downstream through gravity outlets.
Drawdown
The deliberate or natural reduction of a lake or reservoir water surface elevation.
Evaporation Loss
The invisible volumetric loss of water from a lake surface into the atmosphere caused by heat, sun, and dry winds.