Roselle

Geography

Roselle takes its source with the Puyfraud locality, on the commune of Saint-Bonnet-Briance. It sprinkles then the communes of Saint-Genest-on-Roselle, Saint-Paul and Saint-Hilaire-Bonneval before being thrown in the Briance, with 230 meters of altitude.

Hydrology

The flow of Roselle was observed during one 31 years period (1966-1997), with Saint-Hilaire-Bonneval, locality of the department of the High-Vienna located at the level of its confluence with the Briance. Surface thus studied is of 125 km ², that is to say it quasi totality of the catchment area of the river.

The interannual medium flow or module of the river with Saint-Hilaire-Bonneval is of 1,60 m ³ a second.

Roselle presents seasonal fluctuations of flow marked enough, like very often in the basin of Vienna. The high waters are held in winter and at the beginning of spring, and are characterized by average monthly flows going from 1,96 to 2,98 m ³ a second, from December to April included, with a maximum enough Net in January (2,72 m ³ a second) and in February (2,98 m ³ a second). From March however, the flow decreases gradually to the low waters of summer which take place from July to September included, involving a fall of the average flow monthly to the floor of 0,483 m ³ in August, which remains consistent. But these monthly averages are only averages and hide more marked fluctuations over short periods or according to the years.

With the low water levels, the VCN3 can fall until 0,140 m ³ a second (140 liters), in the event of dry period quinquennial, which is far from being very severe. This profile meets the standard of the rivers of the high Limousin (see note).

The risings, as for them, can be very important, taking into account the size exigüe of the catchment area. The QIX 2 and QIX 5 are worth respectively 32 and 46 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 55 m ³ a second, the QIX 20 of 63 m ³, while the QIX 50 is assembled to 75 m ³ a second (see note). That means for example that every five years rising of about 46 m ³ a second must statistically occur, which is considerable for a river of this size.

The recorded maximum instantaneous flow with Saint-Hilaire-Bonneval was of 91,5 m ³ a second on September 22nd, 1993, while the value maximum day laborer was of 45,8 m ³ a second the same day. If one compares the first of these values on a QIX scale of the river, one notes that this rising largely higher than raw the cinquantennale was defined by the QIX 50, and thus completely exceptional.

Roselle is an abundant river. The Lame of water past in its catchment area is of 406 millimetres annually, which is definitely higher than the overall average of France, and also to the average of the basin of the the Loire (more or less 245 millimetres) and of the Vienna (319 millimetres). It is however somewhat lower than the basin of the Briance (432 millimetres). The specific Flow (or Qsp) reached the solid figure of 12,8 liters a second and per square kilometer of basin.

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