Arroux

The Arroux is an affluent of Right Bank of the the Loire, born in Gold Coast and traversing 120 kilometers in the departments of Coast-in Or and Saône-et-Loire. It is thrown in the Loire with Digoin.

The river can have extremely important risings making pass its flow to 530 cubic meters a second (recorded maximum rising with Digoin, October 1965)

Geography

Situation

Located in the middle of the Burgundy, the basin of Arroux is located at the limit of division of water between 3 large French rivers: The the Loire (of which it forms part), the the Rhone (in the East), and the the Seine (in North). One finds there the channel of the Center which constitutes a hydrological connection between the basins of the Loire and the Rhone. The basin recovers approximately 160 communes whose majority are in Saône-et-Loire. The average altitude of the basin is of 394m, the culminating points are in the solid mass of the Morvan which constitutes natural separation between the Loire and the Seine.

Landscapes

Having a geology not very favourable with the cultures (granitic base with development of acid grounds), and a relief relatively undulating, landscapes of Bocage were set up on the basin of Arroux. The breeding of the ox charolais is there dominating.

Principal affluents

the river Lacanche (left bank)
Pontin (left bank)
Drée (left bank)
the Ternin (Right Bank)
the Saddle or river of Cussy (Right Bank)
the Méchet (Right Bank)
the Mesvrin (left bank)
the Bourbince (left bank)

Hydrology

The flow of Arroux was observed over one 50 years period (1958-2007), with Digoin, locality of the Département of Saône-et-Loire, located at the level of its confluence with the Loire. At this place the catchment area of the river is of 3 166 km ².

The interannual medium flow or module of the river with Digoin is of 34,2 m ³ a second, including more than 7,5 m ³ for the Bourbince which enlarges Arroux of its water to little distance upstream.

Arroux presents the rather important and typical seasonal fluctuations of flow of the rivers of the basin ligérien resulting from the Massif Central (let us recall that Morvan in fact part), with high waters of winter carrying the average monthly flow between 51 and 72 m ³ a second, from December to March included (maximum in January), and of low waters of summer of mid-June at September, with a fall of the monthly medium flow up to the level of 6,84 m ³ in August.

The VCN3 can fall until 1,4 m ³, in the event of dry period quinquennial what is very low (see note).

In addition, the risings are often extremely important and can become devastators. Indeed, the recorded maximum instantaneous flow was of 530 m ³ a second on October 1st, 1965, while the value recorded maximum day laborer was of 429 m ³ a second on October 2nd of the same year. The QIX 2 and QIX 5, or calculated flows of biennial and quinquennial rising, are worth respectively 260 and 370 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 440 m ³ a second, while the QIX 20 or flow calculated for a vicennial rising is assembled to 520 m ³ a second. As for the QIX 50, it is of 610 m ³, that is to say nearly two thirds of that of the Yonne (960 m ³ a second) for example (see note).

As comparison, let us recall that the QIX 10 of the Marne at Gournay-sur-Marne in the Paris and its suburbs is worth 510 m ³ a second, while its QIX 50 is of 650 m ³. One notices thus that the QIX 10 as the QIX 50 of the secondary river which would be Arroux brings closer to those from the Marne in Paris.

The Lame of water past in the basin of Arroux is of 342 millimetres annually, which is rather high, a little higher than the average overall of France, but also higher than that of the whole of the catchment area of the Loire (244 millimetres with Montjean, 249 in Nantes). The specific Débit (or Qsp) is assembled at 10,8 liters a second and per square kilometer of basin.

References

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