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A chart datum is the water level surface serving as origin of depths displayed on a nautical chart and for reporting and predicting tide heights. A chart datum is generally derived from some tidal phase, in which case it is also known as a tidal datum. [1] Common chart datums are lowest astronomical tide (LAT) [1] and mean lower low water (MLLW).
Tide tables, sometimes called tide charts, are used for tidal prediction and show the daily times and levels of high and low tides, usually for a particular location. [1] Tide heights at intermediate times (between high and low water) can be approximated by using the rule of twelfths or more accurately calculated by using a published tidal ...
Tidal range is the difference in height between high tide and low tide. Tides are the rise and fall of sea levels caused by gravitational forces exerted by the Moon and Sun, by Earth's rotation and by centrifugal force caused by Earth's progression around the Earth-Moon barycenter. Tidal range depends on time and location.
Tide flow information is most commonly seen on nautical charts, presented as a table of flow speeds and bearings at hourly intervals, with separate tables for spring and neap tides. The timing is relative to high water at some harbour where the tidal behaviour is similar in pattern, though it may be far away.
The approximate location of Pedra Branca in the South China Sea in relation to the countries surrounding it. Pedra Branca, located at 1° 19′ 48″ N and 104° 24′ 27″ E, is an island with an area of about 8,560 square metres (92,100 sq ft) at low tide.
King tides are the highest tides. They are naturally occurring, predictable events. Tides are the movement of water across Earth's surface caused by the combined effects of the gravitational forces exerted by the Moon, Sun, and the rotation of Earth which manifest in the local rise and fall of sea levels.
In many parts of the world the tides approximate to a semi-diurnal sine curve, that is there are two high- and two low- tides per day. As an estimate then each period equates to 1 hour, with the tide rising by 1, 2, 3, 3, 2, finally 1 twelfths of its total range in each hour, from low tide to high tide in about 6 hours, then the tide is ...
In coastal areas, because the ocean tide is quite out of step with the Earth tide, at high ocean tide there is an excess of water above what would be the gravitational equilibrium level, and therefore the adjacent ground falls in response to the resulting differences in weight. At low tide there is a deficit of water and the ground rises.