Analysis of US and Canadian 2017 and 2018 Great Lakes seasonal water level data to update the IGLD

Session: A Possible New Paradigm to Improve the International Great Lakes Datum and Its Maintenance (2)

Adam Grodsky, NOAA/NOS/CO-OPS, [email protected]
Laura Rear McLaughlin, NOAA/CO-OPS, [email protected]
Terese Herron, DFO/CHS, [email protected]
Janelle Laing, DFO/CHS , [email protected]
Cary Wong, NOAA/NOS/CO-OPS, [email protected]

Abstract

An accurate Great Lakes-wide vertical datum is a fundamental requirement for monitoring Great Lakes water levels and supports effective restoration, charting, dredging, international water regulation and power generation. The International Great Lakes Datum (IGLD) requires updating due to varying rates of glacial isostatic adjustment in the Great Lakes. IGLD (1985) is undergoing an update to IGLD (2020), to be published in 2025. One primary change in the new datum will be through the use of a new North American geoid as the reference surface, determined via the use of GNSS to determine the heights instead of leveling to define the vertical datum. Seasonal water level, geodetic leveling and GNSS data sets were collected at several small ports and harbors to help determine the update. Hydraulic correctors (HC) were calculated at each station using two methods; one using an existing interpolation model, the other HCs were directly computed based on comparable differences to a control station on the appropriate lake. These differences, of up to several centimeters, whether from accumulation of systematic errors in leveling or from actual differences in lake topography, will be determined during the seasonal gauge program and are necessary to understand for the IGLD (2020) update.