Alagnon (river)

The Alagnon is a river center of the France. It is a Affluent Allier. It takes its source with the puy Bataillouze (close to Lioran) in the Cantal and is thrown in Combining it in the Département of the Puy-de-Dôme on the level of the commune of Auzat-la-Combelle (formerly baptized Auzat-on-To combine) to the locality the Jump of the Wolf .

Principal affluents

Crossed cities

In the Cantal

in the Haute-Loire

in the Puy-de-Dôme

Hydrology

The annual medium flow of Alagnon, observed during one 41 years period (of 1967 to 2007), with Lempdes-on-Allagnon, locality very close to its confluence, is of 12,2 m ³ a second for a surface of basin of 984 km ² (ref.: ).

Alagnon presents seasonal fluctuations of flow relatively moderate, with one period of high waters of winter-spring characterized by an average monthly flow going from 15,5 to 19,9 m ³ a second, from January to May included (with an in February maximum). As of at the end of May the flow decreases quickly to lead to the period of the low waters which proceeds July at September, with a fall of the monthly medium flow going up to 2,87 m ³ in August, which is still rather consistent, it is true. However the fluctuations of flow can be more important according to the years and over shorter periods.

With the low water level the VCN3 can fall until 0,32 m ³, in the event of dry period quinquennial (see note), that is to say 320 liters a second, which can be regarded as relatively severe for a river of this size.

As for the risings, they can be important taking into account the already large size of the catchment area. They are however less than those which affect the affluents of the Western part of the basin of the Loire, the such Gartempe, the Nantes Sèvre or certain affluents of the Mayenne like the Oudon. The QIX 2 and QIX 5 or calculated flows of biennial and quinquennial rising are worth respectively 120 and 180 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 210 m ³ a second, the QIX 20 of 250 m ³, while the QIX 50 is assembled to 300 m ³ a second (see note).

The maximum instantaneous flow recorded with Lempdes-on-Allagnon during this period, was of 495 m ³ a second on November 5th, 1994, while the recorded maximum daily output was of 237 m ³ a second the same day. If one compares the first of these values on a QIX scale of the river, one notes that this rising was by far higher than a rising cinquantennale, cretainement higher also than the level of a centennial, i.e. in fact, completely exceptional rising.

On the whole, Alagnon is an abundant river. The Lame of water past in its catchment area is of 393 millimetres annually, which is definitely higher than the average of France, all confused basins, and of course also with the average of the basin of the Loire (244 millimetres). The specific Flow of the river (or Qsp) reached of this fact the high figure of 12,4 liters a second and per square kilometer of basin.

References

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