Five things to know about the high equinox tides, an exceptional phenomenon expected in the coming days

Along the coast of the English Channel and the Atlantic Ocean, tidal coefficients could reach 116 at the start of the week. The authorities are calling for extreme caution.

A significant part of the French coastline is preparing for very high tides over the coming days. From Sunday March 10 until Wednesday, “strong tidal coefficients are expected” along the Channel coast and the Atlantic Ocean, warns the Channel and North Sea prefecture. “The region is preparing to welcome the largest tide of the year, and certainly one of the most significant of the decade,” reports to Attitude Manche, the attractiveness agency of the Manche department to the Parisian.

On the coast, municipalities are preparing for particularly high sea levels, as highlighted by France 3 Pays de la Loire. In La Tranche-sur-Mer (Vendée) or on the island of Noirmoutier (Vendée), for example, large sandbags were placed on the dunes to better cope with rising water levels. The town of Le Croisic (Loire-Atlantique) distributed no less than 200 bags to traders and residents.

Franceinfo returns to this phenomenon which promises to be exceptional on the coasts of the north and west of France.

1 High tides which promise to be spectacular

As explained by the Hydrographic and Oceanographic Service of the Navy (Shom), cited by Actu.fr, high tides are “high amplitude tides”, with coefficients – which vary from 20 to 120 – greater than 90. The equinox tides, the strongest, occur every six months, around March-April and September-October. These tides are linked to an alignment of the Earth, Moon and Sun. This straight line causes tides of very large amplitude at the time of the equinox.

“These celestial conditions will be particularly conducive to a spectacular rise in water levels in the Channel” at the start of the week, points out Attitude Manche to the Parisian. In this department as elsewhere along the northern and western coast, these high tides promise to be particularly impressive: the tidal coefficients must in fact be greater than 110 from Sunday, and reach 116 at the start of the week , reports France Bleu. For several days, the ocean will be as high as nearly six meters.

2 Several departments placed on yellow alert

On Saturday, Météo-France placed the coastline of the departments of Finistère, Morbihan, Loire-Atlantique, Vendée, Charente-Maritime and Gironde on yellow alert for “waves-submersion”. Certain departments are also concerned by vigilance for flood risks.

This vigilance will extend to two departments in the South-West on Sunday: Landes and Pyrénées-Atlantiques. According to Alix Roumagnac, director of the Predict risk subsidiary of Météo France, the Bay of Biscay risks being particularly affected. “These high tides will be concomitant with a storm located on the Bay of Biscay, he emphasizes to RMC. We can expect overflows from the water passing over the dikes. This can create local flooding or water rising on the quays, in the ports.”

3 Mont-Saint-Michel transformed into an island

From Saturday until Thursday, Mont-Saint-Michel (Manche) turns into an island due to these high tides. The coefficient will be 114 on Monday and will even reach 117 on Tuesday. High water time will take place after sunrise, which will allow local residents and tourists to better admire the landscape.

As pointed out West France, the ramparts or the footbridge can offer an impressive viewpoint. The regional newspaper also advisesat the Pointe du Grouin du Sud in Saint-Léonard, the Ford of the Epine in Val-Saint-Père, the Marcey-les-Grèves bridge or even Pontaubault to observe the spectacle.

4 The authorities call on the curious “to exercise great caution”

These equinox tides, due to their magnitude this year, will surely arouse the curiosity of local residents along the coast. The maritime prefecture of the Channel and the North Sea “calls for the greatest caution to all users of the sea, and in particular those who fish on foot or who walk on the coast subject to the tide”. High tides cause “a greater mixing of sea water and a faster rise of water“, “They therefore make the sea currents stronger and the sea more dangerous.” “A few minutes can sometimes be enough to be isolated by the rising tide,” recalls the prefect.

The prefecture calls on residents to carefully monitor the weather, tide coefficients and their schedules “before any trip to the sea or on the coast”. It is also strongly recommended to “don’t go out alone” and to keep your loved ones informed: inform them of the place where you wish to go and the planned time of your return. The prefecture adds that it is important to have a way to contact emergency services at sea, such as a cell phone in a waterproof pocket to call 196, or through channel 16 on VHF. Finally, you must stay near a withdrawal point and “preserve a visual landmark on the coastline”.

5 Access to several beaches prohibited

In Gironde or in the Landes, access to several beaches has recently been prohibited, reports France 3 Nouvelle-Aquitaine. Biscarosse (Landes), for example, lost around ten meters of dune in just a few days, against a backdrop of strong currents and violent winds. The municipality has therefore decided to close its beaches for safety reasons.

With the high tides expected at the start of the week, the commune of Lège-Cap Ferret (Gironde) also announced the ban on access to the beaches located in the south of the peninsula. Other beaches are closed, such as La Teste-de-Buch (Gironde).