Vonne

The Vonne is a small French river, traversing the Gâtine poitevine, affluent of left bank of the Clain. It takes its source in Two-Sevres between Vouhé and Reffannes and crosses the departments of the Two-Sevres and the Vienna, in area Poitou-Charentes, until Vivonne where it is thrown in the Clain.

The course of Vonne

Vonne is born in Two-Sevres, in the medium of the fields, an altitude of 223 m, approximately 5 kilometers of the Terrier of Fouilloux, culminating point of the area with its 272 Mr. It furrows then steepsided valleys formed by granitic chaos marking the end of the Armorican Massif. Between Ménigoute and Sanxay, its meanders sprinkle an old Gallo-Roman site . Starting from Curzay-on-Vonne, its bed widens and its curves become longer and full. The country is there more Calcaire…

Affluents

Its principal affluents are:

the brook the Chilleau
the brook the Valouze
the brook the Saint-Germier
list to be supplemented.

Common crossings

Hydrology

Vonne is an abundant river. Its flow was observed over one 39 years period (1969 - 2007), with Cloué, locality very close to its confluence with the Clain. The catchment area of the river is there of 320 km ² is almost the totality of this one.

The interannual medium flow or module of the river with Cloué is of 3,22 m ³ a second.

Vonne presents seasonal fluctuations of flow marked enough. The period of high waters proceeds in winter season, and is accompanied by average monthly flows going from 5,07 to 7,21 m ³ a second, from December to March included (with an in January maximum). As of at the end of March the flow decreases gradually to lead to the period of low waters. Those take place from June to September included, with a fall of the monthly medium flow up to 0,44 m ³ in August, which remains rather acceptable. But 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 0,098 m ³, in the event of dry quinquennial period, that is to say 98 liters a second, which becomes severe, but normal compared with the average of the rivers of the area. The VCN3 is the past minimal quantity or minimal flow over three days consecutive.

As for the risings, they can be very important, following in that the other Western affluents of the the Loire sliding ring (partially) on the old impermeable Armorican base. The QIX 2 and QIX 5 or calculated flows of biennial and quinquennial rising are worth respectively 59 and 97 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 120 m ³ a second, the QIX 20 of 150 m ³, while the QIX 50 is assembled to 180 m ³ a second (see note).

The recorded maximum instantaneous flow with Nailed during this period, was of 177 m ³ a second on December 1st, 1982, while the recorded maximum daily output was of 123 m ³ a second on April 9th, 1983. If one compares the first of these values on a QIX scale of the river, one notes that this rising was of order cinquantennal, and thus exceptional.

Vonne is a river abundant and well supplied with rather important precipitations. The Lame of water past in its catchment area is of 319 millimetres annually, which is more or less equivalent to the overall average of the France all basins confused, 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 a high figure: 10,1 liters a second and per square kilometer of basin.

References

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