Èvre

The Èvre is a French Rivière which runs in the Département of Maine-et-Loire. It is a direct affluent of the the Loire out of left bank.

Etymology

Geography

Èvre takes its source in the commune of Vezins, with a dozen kilometers in the North-East of Bressuire. It throws in the the Loire (left bank) a little downstream from Saint-Florent-the-Old.

Its overall length is approximately 92 kilometers.

Just as for the Nantes Separates and the close Oudon, Èvre and its affluents run on the oriental party of the Armorican solid mass and their water thus runs out on the old impermeable crystalline base.

Hydrology

Èvre is a fairly abundant river, more than the majority of the rivers of plain of the catchment area of the Loire. Its flow was observed over one 41 years period (1967-2007), with the Vault-Saint-Florent, locality of the Département of Maine-et-Loire located at very little distance from its confluence with the the Loire. The catchment area of the river is there of 460 km ² is it quasi totality of this last.

The interannual medium flow or module of the river with the Vault-Saint-Florent is of 3,38 m ³ a second.

Èvre present of the seasonal fluctuations of flow very marked, with high waters of winter-spring carrying the average flow monthly on a level located between 5,34 and 8,6 m ³ a second, from December to March included (with an in January maximum), and low waters of be-beginning of autumn, of June mid-October included, with a fall of the monthly medium flow up to 0,495 m ³ in August, which remains rather consistent. But they are only monthly averages and the fluctuations can be much more important according to the years, or observed over short periods.

Thus with the low water level, the VCN3 can fall until 0,002 m ³ a second, in the event of dry period quinquennial, that is to say 2 small liters a second, which is extremely severe, because the river is thus almost dry. The VCN3 is the past minimal quantity or minimal flow over three days consecutive.

As for the risings, they can be very violent, characteristic shared by the majority of the affluents of the Loire located at the west of the basin (Creuse, Gartempe, Mayenne, Oudon, Sèvre Nantes or Anglin).

Thus the QIX 2 and QIX 5 or calculated flows of biennial and quinquennial rising are worth respectively 72 and 120 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 150 m ³ a second, the QIX 20 of 180 m ³, while the QIX 50 is assembled to 220 m ³ a second (see note).

It is interesting to compare the QIX 2 and QIX 10 of Èvre with those of the Loing, affluent important of the Seine upstream of Paris, formerly famous for the dangerosity of its risings. Whereas the QIX 2 of Èvre is assembled to 72 m ³ a second, that of Loing is worth 99 of them (for a medium flow higher of more than five times than that of Èvre and an area catchment nine times wider). As for the QIX 10, that of Èvre being of 150 m ³ a second, it is assembled to 190 m ³ for Loing. One notices thus that the risings of Èvre are proportionnellemen to the flow, more than four times more important than those of Loing.

The maximum instantaneous flow recorded with the Vault-Saint-Florent during the period of observation, was of 206 m ³ a second on January 12th, 1993, while the value maximum day laborer was of 160 m ³ a second on January 22nd of the same year. By comparing the first of these values on a QIX scale of the river, one notes that this rising was almost of order cinquantennal, and thus relatively exceptional.

On the whole, Èvre is a rather abundant, but extremely irregular river. The Lame of water past in its catchment area is of 233 millimetres annually, which is definitely lower than the overall average of France all confused basins, but approaches much the average of the basin of the the Loire (244 millimetres). The specific Débit of the river (or Qsp) posts of this fact the average figure of 7,4 liters a second and per square kilometer of basin.

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