Orthe

The Orthe is small a French Rivière which runs in the departments of the Mayenne (53) and of the the Sarthe (72). It is an affluent of the the Sarthe out of Right Bank, therefore a tributary of a tributary of the the Loire by the Sarthe and the Maine.

Geography

Orthe takes its source in the high hills (352 m) of the canton of Bais on the territory of the commune of Izé, in the department of the Mayenne. As of its birth, it adopts the direction of the east. It leaves Saint-Pierre-on-Orthe on the right, and enters the department of the the Sarthe to the Large-Forging mill. It passes to north Mount-Saint-Jean, receives on the right, the brook of Demolish , left the ponds of the Forêt of Sillé-the-Guillaume, and sprinkles Douillet, to 2 km upstream of its confluence with the the Sarthe.

Most of its catchment area is within the Regional natural park Normandy-Maine

Common crossings

Orthe crosses or skirts upstream downstream, the following communes:

department of the Mayenne: Izé, Saint-Martin-of-Cone and Saint-Pierre-on-Orthe.
department of the the Sarthe: Montreuil-the-Weak Mount-Saint-Jean, and Soft.

Hydrology

Orthe is a rather abundant river, like the whole of the affluents of the Sarthe resulting from the northern part and the especially North-West of its catchment area. Its flow was observed during one 16 years period (1992-2007), with Douillet, locality of the department of the the Sarthe located at the level of its confluence with the the Sarthe. The catchment area of the river is of 126 km ².

The interannual medium flow or module of the river with Douillet is of 1,20 m ³ a second.

Orthe presents seasonal fluctuations of flow marked well, with high waters of winter carrying the average monthly flow on a level located between 1,90 and 2,58 m ³ a second, from December to March included (with a maximum well Net in January). As of April, the medium flow of the river drops quickly, and this fall continues until the period of low waters. Those take place in summer and at the beginning of the autumn, of mid-June at the beginning of October, involving a fall of the monthly medium flow going up to 0,354 m ³ in September. From October the flow goes up quickly. However the fluctuations of flow are more marked over moreover short periods and according to the years.

With the low water level, the VCN3 can fall until 0,130 m ³, in the event of dry period quinquennial, that is to say 130 liters a second, which is not at all severe for a small river of these dimensions (see note).

The risings, as for them, can be important, taking into account the modest size of the river and of its catchment area. The QIX 2 and QIX 5 are worth respectively 11 and 16 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 20 m ³ and the QIX 20 of 23 m ³ a second, while the QIX 50 was not calculated being given the insufficiency of the duration of observation of the flows, but is estimated at 26 m ³ a second (see note).

The maximum instantaneous flow recorded at the hydrometric station of Soft during this period, was of 19,2 m ³ a second on January 5th, 2001, while the value maximum day laborer was of 15,8 m ³ a second the same day. By comparing the first of these values on a QIX scale of the river, it appears clearly that this rising was hardly of a decennial nature, and thus intended to rather frequently reproduce.

Orthe is a river abundant and well supplied with precipitations of its basin. The Lame of water past in its catchment area is of 301 millimetres annually, which is certainly somewhat lower than the overall average of France, but is definitely higher than the average of the basin of the the Sarthe (201 millimetres with Saint-Denis-in Anjou - without the Dormouse) and of the Mayenne (297 mm without Oudon). The specific Débit of the river (or Qsp) is assembled at 9,5 liters a second and per square kilometer of basin.

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