Tides: Overview

In most places in the world, the ocean's tide is primarily caused by the gravity of the moon and the sun. This dominant part of the tide is complex but regular and is known as the "Astronomical Tide". GeoTide predicts the Astronomical Tide using tidal harmonic analysis. The tidal predictions GeoTide creates can be published in tide tables and can meet the SOLAS/HO requirements. GeoTide also calculate the tidal levels, such as Lowest Astronomical Tide (LAT), Highest Astronomical Tide (HAT) etc. Both tidal predictions and tidal levels are important in shipping, navigation, cartography, hydrography and marine survey.

More on shipping, tidal prediction and harmonic analysis...


The remaining, unpredictable part of the tide is known as the "Residual Tide"; it is mainly caused by weather. This residual part is the difference between the observed and the predicted tide; it includes effects such as tidal surges. Unlike the (astronomical) regular tide, the residual tide is irregular. However GeoTide, using statistical methods, calculates the likelihood of flooding, even though the timing of any flood cannot be determined. This flood probability is used in coastal planning (where it is known also as flood-return period or flood frequency) to assess the likelihood of overtopping of sea defences. It is used to assess the appropriate height of sea defences, in the granting of building licences and in the provision of insurance of coastal propeties and industrial facilities.

More on flooding, return probability and sea-defences...


GeoTide handles both situations; for shipping and hydrography it produces tidal graphs, tide tables and tidal levels; for coastal flooding it produces the flood return frequency as a function of height.