The Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data is responsible for the coordination of the collection, compilation, use, and dissemination of data related to hydraulics, `hydrology, and vertical control for the Great Lakes – St. Lawrence River System. A fundamental requirement for coordinated management is a common height reference system or “vertical datum” by which water levels can be measured and meaningfully related to each other.
The first such vertical datum for the Great Lakes was the International Great Lakes Datum of 1955 (IGLD (1955)). To ensure the vertical datum provides sufficiently accurate heights, it must be adjusted approximately every 30 years to account for the effects of glacial isostatic adjustment (GIA) since the last ice age. GIA is the continuing response of the Earth to the loss of weight of the ice sheets, where areas that were under the ice are rebounding and areas outside the periphery of the ice sheets are subsiding.
IGLD (1955) was updated to IGLD (1985) to account for GIA and, 35 years later, the Coordinating Committee is once again updating IGLD. The Committee’s Vertical Control – Water Levels Subcommittee is overseeing this work and has developed a comprehensive plan. This plan is available in the following formats:
Full Comprehensive Plan