Eyrieux

The Eyrieux is a French Rivière , which runs in the Département of Ardeche. It is an affluent of the the Rhone.

Geography

Eyrieux, flow Right Bank of the the Rhone, is one of the principal Cevennes rivers which come to enlarge this river between Lyon and Avignon. Its basin of an total surface area of 865 km ², represents close to the 3/4 of the area known as of Boutières, of the name of an old Roman way, the via Boteria , which traversed it. It takes its source with the Lake of Devesset with 1  100 meters of altitude.

The whole of the basin lies between the Cevennes chain in the south and the east, to which he is leant (culminating point: Mount Mézenc with   1754 meters) and a less important mountainous edge in the north, which, on the basis of the chain of Boutières, drops gradually to the Rhone. The point low of the basin, with the confluence with the Rhone is with the dimension 95 meters NGF and the median dimension is of 730 meters.

Principal affluents

Principal villages

Hydrology

The interannual medium flow of Eyrieux was observed and calculated over one 27 years period (1965-1991) to Saint-Fortunat-on-Eyrieux. It is assembled to 15,6 m ³ /s (meter-cubic a second) for a surface of basin of 764 km ², that is to say the great majority of its catchment area (910 km ²). The river present of the seasonal fluctuations of flow typical of the Cevennes rain mode, with high waters of autumn and winter at double top, carrying the average monthly flow at a first top of 23,7 m ³ /s in November, then after a fall to 15,9 m ³ /s in December, new and long going top from 21 to 24,5 m ³ /s from January to May (with an in February maximum). A fast fall of the flows follows, finishing in one period of low water level in July - August involving a fall of the monthly medium flow up to the average monthly level of 1,54 m ³ /s in August.

The VCN3 (minimal flow over three days consecutive) can fall up to the very low level of 0,01 m ³, that is to say 10 liters, a second in the event of dry decennial period.

As for the risings, they can be extremely important. Indeed, the QIX 2 or calculated flow of biennial rising and the QIX 5 or flow calculated for a quinquennial rising is worth respectively 435 and 648 m ³ /s, which is very high. The QIX 10 or calculated flow of decennial rising, still much more powerful, is of 788 m ³ /s, while the QIX 20 is assembled to 920 m ³ /s.

The instantaneous maximum flow recorded with Saint-Fortunat-on-Eyrieux over this 17 years period is of 1  350 m ³ /s, that is to say more than the medium flow of the Rhone downstream from Lyon. But the strongest rising known on Eyrieux is of 3  600 m ³ /s in 1857.

The Lame of water past in the catchment area of the river is of 644 millimetres annually, that is to say approximately the double of the French average, all confused basins. The specific Débit (Qsp) is assembled thus at 20,3 liters a second and per square kilometer of basin.

Principal historical risings

; Life century

; IXe century

; XIIe century

; XIIIe century

; XIVe century

; XVe century

  • 1407 : believed in February

; XVIe century

  • 1501 in July

  • 1508 in July
  • 1522 in September
  • 1543 on September 6th
  • 1559 on September 6th
  • 1567 in October
  • 1570 in January, in June and December

; XVIIe century

; XVIIIe century

; XIXe century

  • 1817 : August 26th with 5,74 meters is approximately 2380 m ³ /s in Ollières and 6 meters with approximately 2870 m ³ /s in the St. Lawrence of the Pope

  • 1827: the 11 Ocobre with 5,00 meters is approximately 2100 m ³ /s in the St. Lawrence of the Pope
  • 1840: August 26th with 5,1 meters is approximately 2100 m ³ /s in the St. Lawrence of the Pope
  • 1857: September 10th with 9,65 meters in Ollières and 7 m in the St. Lawrence of the Pope is 3600 m ³ /s approximately in Beauchastel.
  • 1859 : the October 14th and 15th with 5,5 meters in Ollières and 5.5 meters ³ /s in the St. Lawrence of the Pope
  • 1890 is approximately 2500 m: the October 22nd and 23rd with 6,4 meters in Ollières, with 5,5 meters is approximately 2500 m ³ /s in the St. Lawrence of the Pope and 7,45 meters with Beauchastel.
  • 1891 : October 21st with 4,50 meters is approximately 1780 m ³ /s in the St. Lawrence of the Pope

; Since the beginning of the XXe century

August 1st

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