TIDES Tidal coefficient

On the Tide Tables there are tidal coefficients which tell us the amplitude of the tide forecast (difference in height between the consecutive high tides and low tides in any given area).

The highest possible tidal coefficient is 120, corresponding to the greatest high or low tide there can be, excluding meteorological effects. Tidal coefficients are calculated from the following sun and moon parameters: straight ascension, declination, parallax and the distance between the Earth and the celestial body.

Despite tidal coefficients being the same for the whole planet, they affect the amplitude of the tides in a very different manner, depending on where we are. This variation in amplitude is almost null and void in closed seas, apart from where there is local resonance (e.g. it can be up to 3ft in Venice); it is weak in mid-ocean, but tends to be considerably amplified when extending to the continental coasts.

The greatest tides in the world are produced in the Bay of Fundy, Canada (53 ft) and in the Bay of Mont Saint-Michel, France (50 ft).

The amplitude of the tides varies in space and time.

Saint-Malo (France)

There are tides of weak intensity (in the areas close to the terrestrial equator, the tides barely reach tens of centimetres). In other places there are tides of high intensity (for example: the French coasts of the Saint-Malo Bay), where they regularly exceed 30 ft.

The coefficient and therefore the amplitude of the tides follow the phases of the moon with slight disparity during waxing and waning moons; and extensive disparity at times of new moon and full moon. The differences in amplitude between low tides and high tides present great contrasts. In Saint-Malo the difference in level between high tide and low tide is reduced to 10 ft in periods of low tides; and goes as high as 40 ft in periods of high tides.