chart datum

Chart datum is not a horizontal surface but may be considered as such over a limited local area.

However, the elevation assigned to chart datum is slightly different.

On most lakes a single, level surface is adopted as chart datum over the whole lake.

Depths are measured from the chart datum, which is related to the local sea level.

Where the chart datum changes, care should be taken when using tidal predictions for different parts of the river.

If the water level gauge is to continue in operation, its permanent zero would be set to chart datum.

It is used, for example, as a chart datum in cartography and marine navigation.

On most Canadian coastal charts the lower low water, large tide, has been adopted as chart datum.

Increasingly used as chart datum, for example,. for all new Australian charts.

Lakes Michigan-Huron’s level is now only about 10 cm above chart datum.

These predictions are given in feet or meters, with respect to the chart datum for average meteorological conditions.

When levels fall below Chart Datum, actual water depths are less than those shown on the charts.

Water levels on Lake Superior have also risen above its chart datum elevation.

The chart datum varies according to the standard used by each national Hydrographic Office.

Tide tables give the height of the tide above a chart datum.

At this time last year, harbour levels were just at Chart Datum and well below average.

Site bathymetry (depth information should be standardised to Chart Datum).

It is anticipated that the Harbour's level will decline over the next three months, but it should remain above chart datum.

Lake Superior water levels are again below Chart Datum.

The water level at the harbour was below Chart Datum for nineteen days during November.

While levels have declined slightly since that time, they were about one metre above Chart Datum at the beginning of June.

For non-tidal water, the chart datum is set during low-stage years. (Source:

NOTE: These figures are preliminary as chart datum over the whole lake.

Chart Datum should preferably be the same as the datum of tidal predictions for an area.

For water depths more than 3.5m below chart datum, the allowable effective volume flux is fixed at 3.5 cubic metres per second.