Sornin

The Sornin is a French Rivière which runs in the departments of the the Rhone, of the the Loire and Saône-et-Loire. It is a direct affluent of the the Loire out of Right Bank.

Geography

Sornin is thrown in the the Loire (Right Bank) with Pouilly-under-Charlieu, with a dozen kilometers downstream from Roanne.

Affluents

Hydrology

Sornin is a very abundant river, like all the rivers resulting from the Western part of the mounts of the Beaujolais wine. Its flow was observed over one 18 years period (1970-1987), with Charlieu, locality of the department of the the Loire located at about fifteen kilometers to the north-north-east of Roanne, little before its confluence with the the Loire. The catchment area of the river is there of 457 km ² is it quasi totality of this last.

The interannual medium flow or module of the river with Charlieu is of 7,44 m ³ a second.

Sornin, river of medium mountains, present of the seasonal fluctuations of flow very marked, as very often in the east of France, with high waters of winter and spring carrying the average monthly flow on a level located between 9,2 and 14,3 m ³ a second, from December to May included (with an in February maximum), and low waters of summer, July to September, with a fall of the monthly medium flow up to 1,44 m ³ in August. But the fluctuations are much more marked over short periods, and also according to the years.

With the low water level, the VCN3 can fall until 0,075 m ³, in the event of dry period quinquennial, that is to say 75 liters a second, which is very severe for a river of this importance, but rather normal in the north-eastern areas of the Massif Central. Let us recall that the VCN3 is the past minimal quantity or minimal flow over three days consecutive.

As for the risings, they can be very important. The QIX 2 and QIX 5 or calculated flows of biennial and quinquennial rising are worth respectively 130 and 200 m ³. The QIX 10 or calculated flow of decennial rising is of 250 m ³ a second, the QIX 20 of 300 m ³, while the QIX 50 was not calculated, for lack of duration of sufficient observation (see note).

The maximum instantaneous flow recorded at the station of Charlieu was of 339 m ³ a second on May 17th, 1983, while the value maximum day laborer was of 221 m ³ a second on April 26th, 1983. By comparing the first of these values on a QIX scale of the river, it arises that this rising was more than vicennial.

To have an idea of the importance of these flows, one can compare them with one affluents of the Seine in the south-east of Paris, the Loing, famous formerly for his overflows, and somewhat regularized from (the surface of basin is of 4 150 km ²). The QIX 10 of Loing at the end of the course is worth only 190 m ³ (against 250 for Sornin) and its QIX 20 is assembled to 220 m ³ (against 300 for Sornin). Thus in spite of a basin nearly nine times less extended and a medium flow from about 40% of that of Loing, the volume of believed of Sornin carries it largely on those of Loing.

Sornin is an abundant river, supplied with such abundant precipitations they, in the north-eastern areas of the Massif Central. The Lame of water past in its catchment area is of 515 millimetres annually, which is very high, by far higher than the overall average of France, but also largely higher than the average of the basin Allier (326 millimetres with its confluence) and of the Vienna (319 millimetres with Nouâtre). The specific Flow of the river (or Qsp) reached of this fact the robust figure of 16,3 liters a second and per square kilometer of basin.

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