Sounding
Catfish Creek bathymetric soundings at Port Bruce are evaluated to a relative baseline, Chart Datum. The sounding depths are presented from a low-water surface or a low-water datum called Chart Datum (CD). In the Great Lakes area, it is also known as the International Great Lake Datum (IGLD). The International Great Lakes Datum is a reference system used to measure water levels throughout the Great Lakes. The IGLD or Chart Datum for Lake Erie at Port Bruce is 173.5 m.
Chart Datum is selected for Catfish Creek at Port Bruce bathymetric mapping since the water levels seldom fall below it and only very rarely, will there be less depth available than what is identified on a sounding map. In non-tidal waters, Chart Datum is set so that the water level will be above CD approximately 95% of the time.
Chart Datum is the Catfish Creek sounding baseline to which water depths on the map are referenced too. CD is usually taken to correspond to a low-water elevation. Chart Datum found on navigational maps is the lowest predictable level to which the water level is likely to fall. It is the approximate lowest low water. All soundings on a navigational chart are referenced to Chart Datum.
Since studies have identified that Lake Erie water levels effect Catfish Creek water levels up to the Highway 73 Bridge, IGLD was chosen as the baseline for the Port Bruce soundings. Depths on a Catfish Creek at Port Bruce (PB) sounding chart are calculated to Chart Datum. If the water depth were to fall to Chart Datum (173.5m), i.e. relative zero on the PB sounding chart, then the depth shown on the chart would be the actual depth at that time in the river.
If the charted depth and the actual, real-time water depth is known at a specified location then the total depth of water at that location is calculated as, charted depth + water level = water depth
Ice Thickness
