Drac

Etymology

The name of Drac, originally the Drau , is due to an attraction by the occitan drac “imp”, of Latin dracō “Dragon”. It is documented in the forms Dracum (v. 1100), Dravus (1289), the ribière dou Drau (1545)… and analyzes by the hydronymic root Dur-, gilded and the rental suffix - with the .

The Drave and Droue/Drouette share the same etymology.

Hydrography

It takes its source in the Champsaur and is born from the meeting of Drac Blanc (valley of Champoléon) and of Drac Noir (valley of Orcières in the solid mass of Moure Froid. It is thrown in the Isere downstream from Grenoble in Isere (38).

It is a torrent with which the course is strewn with hydroelectric installations , including four large Barrage S:

Sautet,
Saint-Pierre Cognet,
Monteynard,
Our-Lady-with-Commiers.

Drac has a 130 km length.

The medium flow of Drac on the level of the stopping of Sautet is of 33 m/s.

The rising of the 8 September 9th, 1993 reached an instantaneous flow of 770 m/s

Principal affluents

(D) Séveraisse, 32.9 km, of the Massive of the Jewel cases.
(G) Souloise, 25.6 km, of the Collar of Rabou in the Dévoluy, with the Lake of Sautet.
(D) the Good , 40.1 km,
(G) the Ébron, 32.1 km, is thrown in Drac in the Lac of Monteynard-Avignonet, in the south of Grenoble.
(D) the Romanche, 78.4 km, is thrown in Drac in the south of Grenoble, with Field-on-Drac.
(G) Gresse, 34.6 km, of the Vercors.

Hydrology

The interannual medium flow or module of Drac was calculated during one 14 years period to Fontaine. It is assembled to 102 m ³ a second for a surface of basin of 3 550 km ², are the totality of the catchment area.

The river present of the seasonal fluctuations of flow typical of one at the same time nival and rain mode, with high waters of spring-be due to the snow melt and carrying the average monthly flow on the level from 143 to 179 m ³ from May to July included (with an in May maximum - June), followed by a fast fall leading to a short low water level of end of summer in September, with fall of the monthly medium flow to 68 m ³. As of October the flow goes up, but slightly, under the effect of the rains of autumn, then falls down as of November towards a second low water level of winter in January - February.

With the low water levels, the VCN3 can fall until 10,3 m ³, in the event of dry decennial period. The VCN3 is the past minimal quantity or minimal flow over three days consecutive. In addition the risings can be extremely important in the event of fast thaw or of rains torrential. Indeed, the QIX 2 or calculated flow of rising biennial and the QIX 5 or flow calculated for a quinquennial rising is worth respectively 315 and 400 m ³ a second. The QIX 10, or calculated flow of decennial rising, is of 456 m ³ a second. As for the QIX 20 and QIX 50 they are unfortunately not published (see note).

The recorded maximum instantaneous flow was of 833 m ³ a second, while the value maximum day laborer observed was of 644 m ³.

The Lame of water past in the basin of Drac is of 910 millimetres annually, which is high, much higher than the overall average of France, but also definitely higher than that of the whole of the catchment area of the Rhone (670 millimetres with Valence for a surface of basin of 66 450 km ²). The specific Débit (or Qsp) is assembled at 28,7 liters a second and per square kilometer of basin.

Drac in the valley of the Champsaur

The hydraulic mode of Drac is marked nivo-rain (marked of winter and estival low water level in the low valleys). The minimum flows are also influenced by the many agricultural levies and the exchanges with the alluvial tablecloths (succession of losses and resurgences). Believed of cast iron of snow in spring, more irregular with the autumn.

Water quality is variable according to the section considered:

1A on Drac upstream (1B with the downstream of Orcières),
1B-2 of Anvil-blocks to Chauffayer
return to the normal downstream from the Glaizil.

The course of Drac has a great diversity of mediums and landscapes, gravel pits with the multiple ripisylves. One finds plant species there registered on national red list (rare species of Adonis, on left bank) as well as a rich fauna: Bird X migrating and nicheurs, Batrachian S, Mammalian S with presence of protected spaces.

It is a river of first salmonicole piscicultural-population category: 90% of Trout S fario accompanied by chub S and loaches of let us blageons (on the course downstream). The Drac is of this fact particularly snuffed by the fishing , especially with the fly.

The Drac was the involuntary theater of a dramatic event: a class of children in primary education, arrival to see the habitat of the beaver S, was taken with the trap by the brutal rise of water caused by releasing water of the stopping upstream. Six children and accompanying were drowned.

Tourism

Since the Railroad of Walls, there is a remarkable sight on the valley of Drac and his artificial reserves.

References

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