Bès (river)

Bès is a French Rivière Massif Central which runs in the departments of the Lozere and of the Cantal. It is an affluent of the Truyère out of left bank, therefore a tributary of a tributary of the the Garonne by Truyère, then by the Lot.

Geography

Bès takes its source in the Lozere on the plate of the Aubrac to the Signal of Mailhebiau, and joined the Truyère in the Lac of the reserve of the Barrage of Grandval. It is with horse between the Lozere and the Cantal of which it is the natural border on several kilometers. Downstream from Saint-Juéry, Bès forms throats in the Granite.

Departments and main cities crossed

Cantal:
Lozere: Nasbinals, Grandvals, Saint-Juéry

Principal affluents

the Young stag
the Rioumau
the Bédaule

Hydrology

Bès is a very irregular river, following the example its neighbors affluents of Truyère. Its flow was observed during one 51 years period (1956-2006), with Saint-Juéry, locality of the Département of the Cantal located at the level of its confluence with the Truyère (ref.: ). Surface thus studied is of 283 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-Juéry is of 7,86 m ³ a second.

Bès present of the seasonal fluctuations of flow extremely marked, as it is often the case of the rivers of the Massif Central. The high waters are held in winter and in spring, and are characterized by average monthly flows oscillating between 12,0 and 12,7 m ³ a second, from December to April included (with a maximum extremely light in February). From May, the flow decreases quickly to the low waters of summer which take place from July to September included, involving a fall of the monthly flow average energy to the floor of 1,61 m ³ in August. But these monthly averages are only averages and hide fluctuations much more marked over short periods or according to the years.

With the low water levels, the VCN3 can fall until 0,410 m ³ a second, in the event of dry period quinquennial, which cannot be described as very severe. This profile is frequent among the rivers of the Massif Central resulting from high tops (see note).

The risings, as for them, can be extremely important, taking into account the rather reduced size of the catchment area. The QIX 2 and QIX 5 are worth respectively 170 and 250 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 300 m ³ a second, the QIX 20 of 350 m ³, while the QIX 50 is assembled to step less than 420 m ³ a second, that is to say more than the medium flow from the Loire in Orleans or the Seine in Poissy (see note).

The recorded maximum instantaneous flow with Saint-Juéry was of 465 m ³ a second on November 1st, 1994, while the value maximum day laborer was of 243 m ³ a second on December 24th, 1973. If one compares the first of these values on a QIX scale of the river, one notes that this rising was more than of order cinquantennal, and thus very exceptional.

Bès is a very abundant river. The Lame of water past in its catchment area is of 875 millimetres annually, which is more than 2,5 times superior to the overall average of France, all confused basins, and superior also with the average of the basins of the the Garonne (384 millimetres), of the Lot (446 millimetres), and even of the Truyère (671 millimetres). The specific Flow (or Qsp) reached of this fact the very high figure of 27,6 liters a second and per square kilometer of basin.

Random links: