Truyère - SpeedyLook encyclopedia

The Truyère is a French river Massif Central.

Geography

It takes its source in the forest of Cross-to-Bor in the mountain of the Margeride, to 1450 m of altitude (Lozere, 48), and is thrown in the Lot with the downstream of Entraygues-on-Truyère.

Departments and main cities crossed

Hydrography

Cours: 170 km length with important unevennesses what supported the Hydroélectricité: (Dam Grandval, Dam Sarrans, Stopping of Barthe, Dam Couesque,…), with the detriment of the natural Biotope and the traditional activities such fishings, in particular the Fishing with the fly.

The flow became very irregular since the installation of the Barrage S, with sometimes of the too important lâchers for the river, causing the accelerated erosion of the banks, and sometimes, of the " flows réservés" largely lower than the legal minima, causing death by asphyxiation of the watery species and deposit of fine muds and heavy metals (toxic).

Hydrology

Truyère is a very abundant river, as it is often the case for the rivers resulting from the tops of the French Massif Central. Its flow was observed over one 78 years period (1914-1991), with Entraygues-on-Truyère, locality of the Département of Aveyron located at the level of its confluence with the Lot. The catchment area of the river is there of 3 280 km ², i.e. its totality.

The interannual medium flow or module of the river with Entraygues-on-Truyère is of 69,5 m ³ a second.

Truyère presents seasonal fluctuations of flow marked enough, like very often in the southern half of France. The high waters are held end of the autumn at the beginning of spring and are characterized by an average monthly flow going from 78,6 to 109 m ³ a second, from November to May included. One notes a first top in December (rains) and a second more important in March (rains and snow melt). As of the end of May, the flow decreases quickly to low waters of summer. Those take place from July to September included, involving a fall of the monthly medium flow going until 17,1 m ³ a second in August. But the fluctuations are more marked over moreover short periods, and according to the years.

With the low water level, the VCN3 can fall until 2,3 m ³, in the event of period quinquennial dry, which is severe for a river of this size, but perfectly normal in the southernmost areas of the Massif Central (see note).

The risings, as for them, can be very important. The QIX 2 and QIX 5 or calculated flows of biennial and quinquennial rising are worth 670 and 1 respectively; 000 m ³. The QIX 10 or calculated flow of decennial rising is of 1 200 m ³ a second, the QIX 20 of 1 500 m ³ and the QIX 50 of 1 800 m ³ (see note).

The maximum instantaneous flow recorded at the station of Entraygues-on-Truyère was of 433 m ³ a second on April 26th, 1989, while the value maximum day laborer was of 1 260 m ³ a second on October 9th, 1920. By comparing the second of these values on a QIX scale of the river, it arises that this rising of October 1920 was of a decennial nature, and thus at all exceptional.

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 Yonne, famous for his risings and the threats that historically they made weigh on the town of Paris (Yonne is equipped with a basin of 10 887 km ² and of a medium flow of 95 m ³ a second). The QIX 10 of Yonne at the end of the course is worth 710 m ³ (against 1 200 for Truyère), its QIX 20 is of 820 m ³ (against 1 500 for Truyère), and its QIX 50 is assembled to 960 m ³ (against 1 800 for Truyère). Thus in spite of a basin more twice less extended and a medium flow of less of the three quarters, the volume of believed of Truyère is worth close to the double of those of Yonne.

Truyère is an abundant river, supplied with such abundant precipitations they, in the area of the solid masses of Aubrac and the Cantal in particular. The Lame of water past in its catchment area is of 671 millimetres annually, which is very high, superior of approximately twice with the overall average of France, like with the average of the basin of the Lot (446 millimetres). The specific Flow of the river (or Qsp) reached of this fact the high figure of 21,2 liters a second and per square kilometer of basin.

Principal affluents

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