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Glacial Isostatic Adjustment Analysis

This task from Phase 1 of the IUGLS involved investigating glacial isostatic adjustment (GIA) impacts on water levels and the water level relationship between Lake Michigan-Huron and Lake Erie, and the implications of GIA for St. Clair River conveyance and water balance calculations. The primary GIA analysis focused on ensuring that correct water level data was used to represent the change in head difference between Lake Michigan-Huron and Lake Erie over time by recognizing and accounting for the effects of GIA and the use of the International Great Lakes Datum (IGLD) on recorded water level data. The IUGLS also needed to address the sensitivity of results to the water level averaging period used and the level of rounding applied to apparent relative vertical movement rates, water level estimates and their differences. Finally, due to differential GIA, portions of each of the Great Lakes are either rebounding or subsiding relative to their outlets. As a result, each of the lakes is potentially storing or decanting a small amount of water over time due to the differential tilting of their lake basins. Therefore, the Study undertook an analysis to determine whether the effect of GIA on water balance and net basin supply (NBS) calculations was significant and needed to be addressed as part of the analysis.
Related Projects
GIA Workshop
Review of Apparent Vertical Movement Rates
Great Lakes Volume Changes from GIA
Pre-1960 Parry Sound Water Levels
Huron and Erie Water Level Gauge Analysis
GIA Impacts on Huron - Erie Head Difference