How can water level data be used to determine the depth of the water?
A datum is a base elevation used as a reference. Chart Datum, the datum to which soundings are referenced, for NOAA charts in the Great Lakes is Low Water Datum (LWD). LWD is a fixed datum for each lake relative to International Great Lakes Datum 1985 (IGLD 1985). CO-OPS real-time water level data are presented in inches above or below LWD. Historical data are presented in feet or meters above IGLD85.
