Geography of Switzerland - Hydrology

Hydrology

Switzerland has 6% of all freshwater reserves in Europe. The country shares five river basins and some of the largest lakes in western Europe with its neighbours. It is the source of several major European rivers that ultimately flow into the North Sea (Rhine), into the Mediterranean Sea (Rhone), into the Black Sea (Inn, through the Danube) and into the Adriatic Sea (Ticino, through the Po and Rom through the Adige).

Most of the great Swiss rivers, being in their origin mere mountain torrents, tend to overflow their banks, and hence much has been done to prevent this by embanking them, and regaining arable land from them. So the Rhine (between Bad Ragaz and Lake Constance), the Rhone, the Aar, the Reuss; and in particular the great work on the Linth (1807-1816) carried out by Hans Conrad Escher, who earned by his success the surname of "Von der Linth", and on the Zihl near the lakes of Neuchâtel and Biel, while the diversion of the Kander from its junction with the Aar to a channel by which it flows into Lake Thun was effected as early as 1714.

Switzerland has considerable reserves of groundwater and a large number of lakes, large and small, can be found in most areas. The two most extensive, those of Geneva and of Constance, balance each other, as it were, at the south-west and north-east corners of the land. But neither of these is wholly Swiss, this distinction being claimed by the next in size, that of Neuchâtel, Lake Maggiore (partly Swiss only) coming next in the list, and being followed by the wholly Swiss lakes of Lucerne and of Zurich. Then come Lake Lugano, Lake Thun, Lake Biel, Lake Zug, Lake Brienz, Lake Walenstadt and Lake Murten. These thirteen only are over 20 km2 (7.7 sq mi) in extent. Ten of them are in the Rhine basin (also in that of the Aar), two (Maggiore and Lugano) in that of the Po, and one (Geneva) in that of the Rhone. There are no large lakes in the Swiss portion of the Inn basin, the most extensive being that of Sils. Smaller Alpine lakes such as the Oeschinensee are innumerable, and often constitute popular tourist destination. Since the twentieth century a large number of dams have been built in the Alps and elsewhere, resulting in many artificial lakes. The largest are the Sihlsee and the Lake of Gruyère both approximately 10 km2 (3.9 sq mi) in extent. Also notable is Lac des Dix, withheld by the Grande Dixence, the tallest gravity dam in the world.

In total, lakes and reservoirs contain 50% of the stored water, glaciers 28%, groundwater 20% and rivers 2%.