Datum
Reviewed • Standard Hydrology Definition • WaterLakeLevel
# Datum
In hydrology and surveying, a datum is a reference plane or benchmark that serves as 'elevation zero'. Because the Earth is not a perfect sphere, elevations must be anchored to an agreed-upon geometric reference.
When looking at a lake reading of '680.5 ft', the number is incomplete without stating the datum (e.g. 680.5 ft NGVD29). Mixing datums without applying an adjustment formula can lead to costly dock construction mistakes and boat groundings.
A reference surface or mathematical baseline from which vertical elevations or geographic coordinates are reckoned.
What Is a Vertical Datum?
In hydrology and surveying, a datum is a reference plane or benchmark that serves as 'elevation zero'. Because the Earth is not a perfect sphere, elevations must be anchored to an agreed-upon geometric reference.
When looking at a lake reading of '680.5 ft', the number is incomplete without stating the datum (e.g. 680.5 ft NGVD29). Mixing datums without applying an adjustment formula can lead to costly dock construction mistakes and boat groundings.
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.
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.
Flood Pool
The temporary storage capacity above full conservation pool designed to capture floodwaters and prevent downstream damage.