A meander is a very marked sinuosity of the course of a Fleuve or Rivière which occurs when the slope is very weak.
The term comes from the Greek Maiandros , indicating a river of Turkey to the particularly sinuous course (called the Menderes today). The old Greeks had divinisé it (see the article Méandre (mythology)).
The meanders and the “hairy one” of the rivers evolve/move naturally under the effect of erosion due to the current, this one continuing to erode the concave bank, while alluvia form a deposit on convex bank. With the wire of time, a meander can end up being recut, delimiting a dead Bras.
On the rivers or the upstream of the rivers, species such as the beaver can also intervene by retaining water behind their stoppings
In the agricultural and urban areas , or having made the object of hydraulic installations, the meanders and arm-deaths has tended to quickly regressing then to disappear with the profit from correction from the channels, for more than 500 years in Europe, with various negative consequences:
- acceleration of water flows, implying;
- Flood S more serious and more frequent downstream;
- Dryness S increased upstream;
- aggravation of the erosion, locally;
- ecological disturbances, with Fragmentation écopaysagère and degradation of the Water related to the artificialisation of the banks, and often with the locks and stoppings associated with these installations;
- less food of the ground water, because the surface and often the total volume of water of the course of the rivers decrease, whereas all things being equal, it is the height of water which controls the speed of percolation towards the tablecloth (cf Loi of Darcy).
The rivers for a long time urbanized preserved their principal meanders (p. e.g. the the Seine, in particular downstream from Rouen), but often lost their hairy and the capacity of these meanders to evolve/move, town planning or agriculture seeking to fix them for reasons of protection of the public property or deprived.
Typology
- meanders of valley or meanders boxed: with the wire of the centuries, these rivers cut the rock according to their formation in meanders. Their side displacement is extremely slow, if not absent. Such rivers are incised deeply. A very known example is the river Colorado, with the the United States, which forged the Large Canyon.
- free meanders or of alluvial plain: they spread in the major Lit river; they are very mobile meanders which can leave very wet or abandoned sectors like the Bayou S in the south of the the United States.
Ecology
The meandrisation belongs to the processes known as of disturbance which create new mediums, colonized by the species pionnières, then by a secondary and climacic stage. this phenomenon contributes to heterogeneity and with the biological diversity of the rivers, rivers and Ripisylve S. the meandrisation is a natural phenomenon necessary to the ecological good performance of the rivers, which should be preserved or restored to answer the objectives of good management of water and ecological good state of the Bassin pouring (cf Parent directive on water in Europe), that the retrospective ecology can integrate in the steps of Cartographie of the biological corridors. These processes require that the rivère can freely move in its major bed, which is not very acceptable in the context of private property. In France the documents of town plannings (SCOT in particular) can indicate and protect the zones from evolution of the rivers.
Remarkable meanders
Belgium
-
the Cascade of Coo, more important cascade of Belgium, is resulting from a meander which was recut with the XVIIIe century by the monks of the Abbaye of Stavelot. The dead meander is used henceforth as lower basin for the hydroelectric station of Coo-Three-Bridges;
- a meander of the Lesse was naturally recut by a water loss in a ground Karstique with the Gouffre of Belvaux, around Han-on-Injures, which gave rise to the Grottes of Han (" Han " or " Ham " being a name carried by several localities of Belgium, meaning meander ).
Canada
France
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the meander of Queuille formed by the Sioule in the Department of the Puy-de-Dôme.
- the meander of Besancon formed by the Doubs. The historical center developed inside this meander now called the Loop because of its geometrical form. Jules César, in his Comments on the War of Gaules, thus described the meander of Besancon: “ Doubs surrounds almost the whole city of a circle which one would say traced to the compass; the space which the river leaves free does not measure more than sixteen hundred feet… ”.
- the meander given up by the Screw with Navacelles forming a circus enters the causse of Larzac and the causse of Blandas.
Thailand
- the historical city of Ayutthaya was built on a meander recut by a channel of the Chao Phraya.
See too
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