The Rhone is the great river of the southeast. Rising in the Alps, it passes through Lake Geneva (French: Lac Leman) to enter France, which has 324 miles of its total length of 505 miles. At Lyon it receives its major tributary, the Saone. In eastern France the direction of the main rivers is predominantly north-south through the Alpine furrow. The regime of the Rhone is complex. Near Lyon the Rhone and its important Isere and Drome tributaries, draining from the Alps, have a marked late spring-early summer peak caused by the melting of snow and ice.
While this peak is generally characteristic of the river as a whole, it is considerably modified by the contribution of the Saone, of the Durance, and of some tributaries in the Mediterranean south as a result of the fall-winter rainfall peak. Thus the powerful Rhone has a remarkably ample flow in all seasons. The course of the river and the local water tables has been much modified by a series of dams to generate power and to permit navigation to Lyon. The Rhone also supplies cooling water to a series of atomic power stations.
West of the Rhone, the Bas Rhone-Languedoc canal, constructed after World War II to provide irrigation, has proved to be an essential element in the remarkable urban and industrial development of Languedoc. East of the Rhone the Canal de Provence taps the unpolluted waters of a Rhone tributary, the Durance, supplying Aix-en-Provence, Marseille, Toulon, and the coast of Provence with drinking water and providing impetus for urban expansion. At its delta, beginning about 25 miles from the Mediterranean, the Rhone and its channels deposit significant amounts of alluvium to form the Camargue region.
The Rhine system The Rhine forms the eastern boundary of France for some 118 miles. In this section its course is dominated by the melting of snow and ice from Alpine headstreams, giving it a pronounced late spring-summer peak and often generally low water in autumn. The Ill, which joins the Rhine at Strasbourg, drains southern Alsace. The Rhine valley has been considerably modified by the construction on the French side of the lateral Grand Canal d’Alsace, for power generation and navigation.
The eastern Paris Basin is drained by two tributaries, the Moselle, (partly canalized), and the Meuse; the former reaches the Rhine by way of Luxembourg and Germany, and the latter, as the Maas (Dutch), reaches the Rhine delta at the North Sea by way of Belgium and The Netherlands. The Seine system The main river of the Paris Basin, the Seine, 485 miles (780 kilometres) in length, is joined upstream on the left bank by its tributary the Yonne, on the right bank south of Paris by the Marne, and north of the city by the Oise.
While the Seine has a regular flow throughout the year, there may be flooding in the spring and, occasionally more severely, during the customary fall-winter peak of lowland rivers. Efforts have been made to reduce flooding on the Seine and its tributaries by the building of reservoirs. A number of islands dot the Seine along its meandering, generally westward course across the central Paris Basin and through the capital city itself. One of these, the Ile de la Cite, forms the very heart of the city of Paris. Eventually the river enters the English Channel at Le Havre.