The Seine ( , ) is a river in northern France. Its drainage basin is in the Paris Basin (a geological relative lowland) covering most of northern France. It rises at Source-Seine, northwest of Dijon in northeastern France in the Langres plateau, flowing through Paris and into the English Channel at Le Havre (and Honfleur on the left bank). It is navigable by ocean-going vessels as far as Rouen, from the sea. Over 60 percent of its length, as far as Burgundy, is negotiable by large barges and most tour boats, and nearly its whole length is available for recreational boating; excursion boats offer sightseeing tours of the river banks in the capital city, Paris.
There are 37 bridges in Paris across the Seine (the most famous of which are the Pont Alexandre III and the Pont Neuf) and dozens more outside the city. A notable bridge, which is also the last along the course of the river, is the Pont de Normandie, the ninth longest cable-stayed bridge in the world, which links Le Havre and Honfleur.
Sources
The Seine rises in the commune of Source-Seine, about northwest of Dijon. The source has been owned by the city of Paris since 1864. A number of closely associated small ditches or depressions provide the source waters, with an artificial grotto laid out to highlight and contain a deemed main source. The grotto includes a statue of a nymph, a dog, and a dragon. On the same site are the buried remains of a Gallo-Roman temple. Small statues of the dea Sequana "Seine goddess" and other ex-votos found at the same place are now exhibited in the Dijon archaeological museum.
Course
The Seine can artificially be divided into five parts: the Petite Seine, "Small Seine" from the sources to Montereau-Fault-Yonne the Haute Seine, "Upper Seine" from Montereau-Fault-Yonne to Paris the Traversée de Paris, "the Paris waterway" the Basse Seine, "Lower Seine" from Paris to Rouen the Seine maritime, "Maritime Seine" from Rouen to the English channel.
Below Rouen, the river passes through the Parc Naturel Régional des Boucles de la Seine Normande, a French regional nature park.
Navigation
The Seine is dredged and ocean-going vessels can dock at Rouen, from the sea. Commercial craft (barges and push-tows) can use the river beginning at Marcilly-sur-Seine, to its mouth.
At Paris, there are 37 bridges. The river is only above sea level from its mouth, making it slow flowing and thus easily navigable.
The Seine Maritime, from the English Channel at Le Havre to Rouen, is the only portion of the Seine used by ocean-going craft. The tidal section of the Seine Maritime is followed by a canalized section (Basse Seine) with four large multiple locks until the mouth of the Oise at Conflans-Sainte-Honorine (). Smaller locks at Bougival and at Suresnes lift the vessels to the level of the river in Paris, where the junction with the Canal Saint-Martin is located. The distance from the mouth of the Oise is .
The Haute Seine, from Paris to Montereau-Fault-Yonne, is long and has 8 locks. At Charenton-le-Pont is the mouth of the Marne. Upstream from Paris seven locks ensure navigation to Saint Mammès, where the Loing mouth is situated. Through an eighth lock the river Yonne is reached at Montereau-Fault-Yonne. From the mouth of the Yonne, larger ships can continue upstream to Nogent-sur-Seine (, 7 locks). From there on, the river is navigable only by small craft to Marcilly-sur-Seine (, 4 locks). At Marcilly-sur-Seine the 19th century Canal de la Haute-Seine used to allow vessels to continue all the way to Troyes. This canal has been abandoned since 1957.
The average depth of the Seine today at Paris is about . Until locks were installed to raise the level in the 1800s, the river was much shallower within the city, and consisted of a small channel of continuous flow bordered by sandy banks (depicted in many illustrations of the period). Today the depth is tightly controlled and the entire width of the river between the built-up banks on either side is normally filled with water. The average flow of the river is very low, only a few cubic metres per second, but much higher flows are possible during periods of heavy runoff.
Dams and flood control
Four large storage reservoirs have been built since 1950 on the Seine as well as its tributaries Yonne, Marne, and Aube. These help in maintaining a constant level for the river through the city, but cannot prevent significant increases in river level during periods of extreme runoff. The dams are Lac d’Orient, Lac des Settons, Lake Der-Chantecoq, and Auzon-Temple and Amance, respectively.