Coastal navigation


The first requests for sea level information arose from the needs of inshore navigation and access to ports with substantial tidal ranges. There was a need for real-time or only slightly time-delayed measurements. 


Entrée de la Penfeld, Port militaire de Brest (Crédits SHOM - Nicolas Pouvreau, juillet 2012)



To meet this need, the information was obtained by direct vision:

  • Either from the tide staff available at the entrance to ports or along channels in the maritime portion of rivers;
  • Or, in the major seaports, daytime signals using cones and cylinders, and night-time signals using green, red and white lights.


Détail des échelles de marée positionnées à l'entrée de la Penfeld, Port militaire de Brest (Crédits SHOM - Nicolas Pouvreau, juillet 2012)



More modern systems were developed in some estuaries where water depths measured at different tide stations were transmitted by radio to ships, in particular VHF voice radio (Port of Nantes - Saint-Nazaire, Port of Bordeaux , Port of Rouen).


Observatoire marégraphique de Nantes Salorges (Crédits SHOM - Nicolas Pouvreau, 21 juin 2012)



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