New analysis of Low Water Datum in conjunction with the International Great Lakes Datum 2020 update

Session: A Possible New Paradigm to Improve the International Great Lakes Datum and Its Maintenance (1)

Chris Zervas, NOAA/NOS/Center for Operational Oceanographic Products and Services, [email protected]
Derrick Beach, Environment and Climate Change Canada, [email protected]
Laura Rear McLaughlin, NOAA/CO-OPS, [email protected]
Terese Herron, DFO/CHS, [email protected]
Colleen Roche, NOAA/ Office of Coast Survey , [email protected]

Abstract

High and low water datums are important references for safe waterway navigation and coastal infrastructure development. Water levels in the Great Lakes are referenced to the International Great Lakes Datum (IGLD), a common datum adopted in 1955 between the U.S. and Canada. Nautical charts in the Lakes are referenced to Chart Datum (Low Water Datum), expressed in terms of IGLD heights. Chart Datum values were set to a level “so that water levels will seldom fall below them”. The IGLD has been updated in the past, most recently from IGLD (1955) to IGLD (1985), to account for glacial isostatic adjustment of the earth’s crust, and in turn applied to Chart Datum. The impact of variable and potentially changing water levels in the Great Lakes has not been examined for some time. As IGLD (1985) is being updated to IGLD (2020), it provides an opportunity to evaluate Low Water Datum. Extreme values analysis using water level data from 1918-2017 for various periods is being undertaken, with comparisons made to current Low Water Datum values. The results will be used in determining the need to make changes to the Low Water Datum as the new IGLD (2020) is adopted.