International Great Lakes Datum

The International Great Lakes Datum (IGLD) is a common reference system used to measure water level heights throughout the Great Lakes, their connecting waterways, and the St. Lawrence River System. A common system is needed for marine navigation, water level regulation, water management, surveying, mapping, and shoreline use planning. Established in 1955, the IGLD is a binational effort between the United States and Canada that ensures cohesive water management in eight states and two provinces. The IGLD is managed by a binational group of federal scientists known as the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data and its Vertical-Control Water-Levels SubCommittee (SC).

The 2020 Update: A New IGLD Is Coming!

To account for movements of the Earth’s crust and accurately measure water levels, the IGLD needs to be updated approximately every 25-30 years. CO-OPS and its partners currently utilize IGLD 1985. This existing IGLD will be revised over the next several years and replaced by IGLD (2020). As part of the revision, the SC will also evaluate and potentially revise the Low Water Datum (LWD). IGLD (2020) will align with the National Geodetic Survey’s new geoid-based North American-Pacific Geopotential Datum. The new IGLD is scheduled for tentative release in 2027.

Image displays the resulting tilting of the region as determined by high accuracy GPS measurements.
In the Great Lakes, Glacial Isostatic Adjustment (e.g. movement of the Earth's crust) is a primary contributing factor to changes in IGLD and a significant reason behind why IGLD must be periodically updated. The above image displays the resulting tilting of the region as determined by high accuracy GPS measurements in units of mm/year. Source: M. Craymer and C. Wisotzkey, 2021.
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