Lignon of Velay

The Lignon of Velay is a river of France, taking its source in Velay, in the department of the Haute-Loire and throwing themselves in the the Loire out of Right Bank.

It should not be confused with the Lignon of Drill, which is thrown in the Loire out of left bank downstream.

Geography

Lignon of Velay takes its source on the northern slope of the Croix of Peccata , in the Solid mass of the Mézenc (Mounts of the Vivarais).

Hydrography - affluents

Although length only of approximately 85 kilometers, Lignon in particular has several affluents of which:

the Sérigoule
the Auze
the Dunière

There exist several stoppings on its course:

Lavalette (which feeds Saint-Etienne out of drinking water)
the Chapelette
the Vendets
the Pont of Lignon

Crossed cities

Fay-on-Lignon
It Chambon-on-Lignon
Tence

Hydrology

Lignon of Velay is an abundant river, like the majority of the rivers resulting from the mounts of the French Massif Central. Its flow was observed over one 70 years period (1936-2005), with Yssingeaux, city of the Haute-Loire located upstream confluence of the Dunière from which the flow is excluded, but was been the subject of a separate analysis. The catchment area of the river is there of 350 km ² what accounts for 53% of its totality more or less.

The interannual medium flow or module of the river with Yssingeaux is of 6,23 m ³ a second.

Lignon of Velay presents seasonal fluctuations of flow extremely marked, with high waters going of the end of the autome in spring, and carrying the average monthly flow on a level located between 7,71 and 9,43 m ³ a second, from November to May included (with an in March maximum). This long period is followed of a fast fall in June, driving with low waters of summer, at the beginning of July at September included, with a fall of the monthly medium flow up to 1,37 m ³ in August, which very low, is not compared to the good of other affluents of the Loire. The fluctuations of flow can however be more important over shorter periods.

With the low water level the VCN3 can fall until 0,16 m ³, in the event of dry quinquennial period, that is to say only 160 liters a second, which is severe. For recall, the VCN3 is the past minimal quantity or minimal flow over three days consecutive.

As for the risings, they can be important, characteristic divided by the majority of the affluents of the Loire. The QJ 2 and QJ 5 or calculated daily outputs of biennial and quinquennial rising are worth respectively 70 and 110 m ³ a second. The QJ 10 or calculated daily output of decennial rising is of 130 m ³ a second, the QJ 20 of 160 m ³, while the QJ 50 is assembled to 190 m ³ a second (see note).

The recorded maximum daily output with Yssingeaux during this period, was of 517 m ³ a second on January 22nd, 1995. By comparing this value on a QJ scale of the river, one notes that this rising was with more twice higher than the calculated flow the of raw one cinquantenale, and thus completely exceptional.

On the whole, Lignon of Velay is an abundant river. The Lame of water past in its catchment area is of 563 millimetres annually, which is largely higher than the overall average of France all confused basins, but especially much higher than the average of the basin of the the Loire (244 millimetres). The specific Débit of the river (or Qsp) posts of this fact the robust figure of 17,8 liters a second and per square kilometer of basin.

References

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