Spring tides are exceptional natural phenomena.
Their appearance is influenced by the stars and planets.
When the moon, the sun and the earth play the same part and align, the movements of the sea become greater, creating the great tides.
Find out more about these immense waves and their impact on our coastal environment.
What is the definition of spring tides?
Spring tides are waves with exceptional amplitudes.
These are not the classic tides that can be observed every day, such as diurnal tides (one high tide and one low tide per day) or semi-diurnal tides (two high tides and two low tides per day).
Spring tides are periodic variations in sea level that occur with the gravitational pull of the Moon and Sun on the Earth and create significant differences between high and low tides.
All the planets in the solar system have an effect on high tides, but especially the Moon and the Sun due to their close distance from the earth.
There is a period of high tides approximately every 14 days which corresponds to a lunar cycle.
It is characterized by higher high tides and lower low tides than usual.
This rapid fluctuation in sea levels can also surprise walkers.
The tidal coefficient is used to calculate the tidal range, which is the difference between the height of high tide and that of the next low tide.
Taking into account several criteria, notably the position of the planets, this figure is generally between 20 and 120. The higher it is, the greater the tide will be.
We speak of high tide when it exceeds 100.
What are the different types of spring tides?
Also called spring tides, high syzygy tides occur when the Earth, Moon and Sun are perfectly aligned.
The trio then benefits from optimal gravity.
This phenomenon appears during the full moon and the new moon.
Equinox tides occur at two times of the year when the length of day is equal to the length of night.
The equinoxes occur around March 20 or 21 (spring equinox) and around September 22 or 23 (autumn equinox).
Several high tides have remained engraved in history.
For example, in 2015, in the bay of Mont Saint-Michel, a coefficient of 119 and a tidal range of 14.15 m were observed.
It was the “tide of the century”.
The term
"King tide"
is used to describe exceptionally high tides and these are often syzygian king tides.
Venice is also affected by frequent flooding.
In 2019, water levels reached 1.87m, one of the highest recorded.
What are the causes of the appearance of spring tides?
Spring tides are therefore linked to the interaction of gravity between the Earth, the Moon and the Sun.
The alignment of these 3 celestial bodies creates the perfect configuration for the phenomenon of syzygy.
During these periods, the sun and the moon pool their action and reinforce their effect on the oceans.
The moon has an even greater influence when it is in the full moon or new moon phase.
Even if the gravitational force of the sun is less important due to its distance from the earth, its alignment is essential to create the spring tides.
Indeed, it is the combination of solar and lunar tides that create these exceptionally high tides.
Furthermore, the notion of perigee is also important in the process of spring tides.
Perigee is the point where the moon's orbit is closest to that of the earth, further increasing its power in creating these large waves.
What are the factors that influence spring tides?
Several terrestrial factors modify the amplitude of spring tides.
The latter are different from one region to another, because the relief (cliffs, hills, etc.) and the shape of the coasts (bays, beaches, etc.) influence the way in which they propagate and amplify.
The topography of the seabed also plays an important role by creating funneling, resonance or channeling effects which favor high tides, without forgetting the direction and speed of the currents.
Weather conditions, such as storms, also impact water levels.
Weather conditions accentuate high tides such as strong swells, gusts of wind or cyclones.
All of these elements are not primarily responsible for the formation of high tides, but they can aggravate their power.
How important are high tides for the coasts?
Spring tides are not only impressive natural phenomena that attract many tourists, they also have important ecological, economic and social issues for coastal regions.
High tides promote marine biodiversity.
Seaside areas are home to rich ecosystems that are adapted to tidal variations.
This marine wealth is a source of food for marine and terrestrial species, such as birds.
High tides also allow migratory movements of certain species, which are necessary for their reproduction, survival and the proper distribution of species in the ecosystem.
The strong currents associated with high tides act on the dynamics and distribution of sediments (sand, pebbles, mud, etc.) which are deposited along the coasts.
This contributes to the formation of beaches or sandbars.
Finally, the energy released by high tides is a renewable energy source which is exploited to produce electricity.
What are the consequences of high tides?
High tides can have harmful consequences.
Flooding and threats to residents and infrastructure.
Although high tides are a natural and frequent phenomenon, they can sometimes lead to flooding in certain areas and even more so when other extreme weather conditions occur.
High water levels can submerge low-lying coastlines, affecting residents, agricultural land and infrastructure (ports, dykes, jetties, quays, homes, businesses, hotels, etc.).
Certain professions are even more concerned, such as fishermen and sailors who must take into account variations in water levels in their daily lives.
Impact on fauna and flora.
High tides intensify the process of coastal erosion.
Powerful waves can degrade or destroy beaches and cliffs.
Rapid fluctuations in water levels can affect certain species, create ecological imbalance, changes in marine communities, disruption of reproduction and change in migratory paths.
Furthermore, if waves overcome natural dams such as dunes, they can increase the salinity of coastal waters.
Salt water from the sea enters areas where the water was once fresh.
This has effects on flora and drinking water.