Thouaret

The Thouaret is a French Rivière which runs in the department of the Two-Sevres (79). It is an affluent of the Thouet out of left bank, therefore a tributary of a tributary of the the Loire by Thouet.

Geography

Thouaret occurs on the territory of the commune of Chanteloup, close to the Vault-Saint-Laurent, with six kilometers in the south of Bressuire. Shortly after its birth, it is directed towards the North-East, direction which it maintains throughout the remainder of its course of almost 52 kilometers. It is thrown in the Thouet (left bank) with Maulais, with a few kilometers upstream of Thouars.

Affluents

Gatine
Joyette
the Sleeve

Hydrology

Thouaret is a not very abundant river. Its flow was observed over one 37 years period (1971-2007), with Luzay, locality located little before its confluence with the Thouet. The catchment area of the river is there of 308 km ² (either its almost totality).

The interannual medium flow or module of the river with Luzay is of 1,74 m ³ a second.

Thouaret presents seasonal fluctuations of flow very marked, with one period of high waters of winter carrying the average monthly flow on a level located between 2,9 and 4,8 m ³ a second, from December to March included (with an in January maximum - February). As of at the end of March the flow decreases gradually to lead to the period of the low waters which proceeds June at October included, with a fall of the monthly medium flow going up to 0,048 m ³ in August, i.e. 48 liters a second, which is severe for a river of this size. However the fluctuations of flow can be even more important according to the years and over shorter periods.

With the low water level the VCN3 can fall until 0,001 m ³, in the event of dry quinquennial period, that is to say 1 liter a second, which is extremely severe, the river being thus almost dry. The VCN3 is the past minimal quantity or minimal flow over three days consecutive.

As for the risings, they can be extremely important taking into account the exiguity of the catchment area. Being given the impermeability of the basement, they are not less than those of the affluents of Mayenne (the Oudon for example) or of the Vilaine (the Semnon). The QIX 2 and QIX 5 or calculated flows of biennial and quinquennial rising are worth respectively 37 and 59 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 73 m ³ a second, the QIX 20 of 87 m ³, while the QIX 50 is assembled to 100 m ³ a second (see note).

The recorded maximum instantaneous flow with Luzay during this period, was of 77,5 m ³ a second on January 22nd, 1995, while the recorded maximum daily output was of 65 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 not even of a vicennial nature (20 years), and thus intended to rather frequently reproduce.

It can be interesting to compare the QIX 2, QIX 10 and QIX 20 of Thouaret to those of the Yvette to Villebon-sur-Yvette, affluent of left bank of the Orge, running upstream of Paris, whose module is assembled to 1,34 m ³ a second, having a basin of 224 km ² (either about less vast 25%), and having produced some disastrous overflows these last decades. Whereas the QIX 2 of Thouaret is assembled to 37 m ³ a second, that of the Yvette is worth 9,4 of them. As for the QIX 10, that of Thouaret being of 73 m ³ a second, it is of 15 m ³ for the Yvette. Finally tandis the QIX 20 of Thouaret is assembled to 87 m ³ a second, that of the Yvette reaches only 17 m ³ a second. One will conclude from it that the risings of Thouaret are proportionally more than three times more important than those of the Yvette, river presenting serious risks however. On the whole, Thouaret is a not very abundant river. The Lame of water past in its catchment area is of 178 millimetres annually, which is much lower than the overall average of France all confused basins, but also of the basin of the Loire (244 millimetres). The specific Flow of the river (or Qsp) reached of this fact the rather poor figure of 5,6 liters a second and per square kilometer of basin.

References

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