RIVERS AND RIVERS

rivers and rivers

The rivers and the rivers are  rivers. The rivers are thrown in the sea, while the rivers are thrown in other rivers.

RIVERS

From which do the rivers come?

The rivers have different origins: it is what is called  the modes.

–the glacial mode: in high mountain,  the cast iron of the glaciers  gives birth to from the brooks and the torrents which form the rivers (like the Rhone or the Rhine in Europe);

–the nival mode: when there are no mountains, but much of snow, as in certain areas of Canada, in Siberia or in the countries of Northern Europe, in fact  the snow melt  forms the rivers;

–the rain mode: the rivers also come from rainwater, the streaming or the underground water tables (of the water reserves), which take the shape of  sources  emerging from the ground: it is the case of the Seine and the Loire in France.

The mode of the rivers

The rivers receive  affluents  or tributaries which come to reinforce them, then they are thrown in the sea by the intermediary of  an estuary  (like the Gironde or the Loire in France) or of  a delta  (like the Nile in Africa or the Amazon in South America). A river and its affluents form  a catchment area. Certain rivers (like the Nile, the Amazon or Yang-tseu-kiang in China) occupy of the surfaces of several million km².

The rivers of the world offer a large variety of  hydrological modes, because of the various types of climates, rocks and vegetation. In general, the large rivers have  a regular  flow.  The modes  are  simple  when only one period ago of low waters and high waters (as for the Seine); they are  complex  when several periods follow one another in the year (like Congo in Africa or the Danube in Europe). In the equatorial and tropical areas, the hydrological mode follows  the pluviometric mode.

With 6 400 km length and an average annual flow of 180 000 m ³  a second, the Amazon  (in South America) is the most powerful river of the world. It also has  a watershed, i.e. a place where the fresh waters are based in salted water; for the Amazon, this line is located at almost 40 km of the coasts, on the open sea.

RIVERS

One distinguishes various types of rivers,  according to the climate and the nature of the grounds and the rocks which they cross:

–temporary rivers: in areas like the Maghreb (in North Africa), when the climate is desert or semi-desert, the permanent rivers are rare; on the other hand, of the rivers to the temporary flow ( wadis) can appear at the time of the rain season and disappear after a few months from dryness;

–the torrential rivers  run out along a strong slope. These  rivers of mountains  are "capricious" and their periods of risings are violent: a river like Gardon (an affluent of the Rhone, in the south of France) can in a few hours see its flow passing from some m³ a second to more than 3 000 m³ a second;

–underground rivers: in fact  seepage waters  penetrate several tens of meters in the basement and create rivers.

THE WORK OF THE RIVERS AND THE RIVERS

Water models the landscapes. The surface rain and waters degrade and erode the rocks by removing layers of sediments. The rivers and the rivers thus dig their  bed  along the way which they traverse (it is their  course): it is for example the valley of the Rhone in France.

A river or a river can have a particularly low flow (the low water level) or particularly high ( the rising): in both cases, it results from them an action and effects favorable and/or harmful on surrounding nature. In the case of the Nile (in Egypt), the annual risings can cause significant damage, but also deposit on the banks a fertile silt which allows the land utilization by agriculture.

TO GO FURTHER

? water on the Earth

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