Allondon

The Allondon is a Rivière free - Suisse a length of approximately 22 kilometers including 17,8 in France (including the zone of free-Switzerland joint ownership). It is a Affluent the Rhone which takes its source with the foot of the Massif of the Jura (close to Echenevex in the French department of the Ain) and throws in the Rhone close to the village of the Plain after having skirted the common Genevese of Dardagny, Russin and Satigny.

Hydrology

Allondon is an extremely abundant river, like all the rivers resulting at least partially from the solid mass of the Jura. Its flow was observed during one 18 years period (1990-2007), with Saint-Genis-Pouilly, locality of the French department of the Ain unfortunately located several away kilometers from its outlet in the the Rhone and upstream of the confluence with its major affluent, the Lion. The catchment area of the river is there of 37,5 km ² (either more or less a third of its totality).

The interannual medium flow or module of the river with Saint-Genis-Pouilly is of 0,866 m ³ a second.

Allondon present of the seasonal fluctuations of flow very marked, as it is very often the case for the rivers of the Jura. The high waters are held autumn in spring (from November to April included) and are characterized by monthly flows oscillating between 0,95 and 1,37 m ³ a second. These risings present two tops strong Nets, the first in November (1,33 m ³ - rains) and the second in March (1,37 m ³ - rains and snow melt). Between these two peaks, it is the winter and the flow drops somewhat with a floor in February (1,10 m ³). As of April, the discharge of river decreases until the period of the low waters of summer which take place from July to September, with a fall of the monthly medium flow going up to 0,241 m ³ in August. But the fluctuations of flow are much more marked over moreover short periods or according to the years.

With the low water level, the VCN3 can fall until 0,011 m ³, in the event of dry period quinquennial, that is to say eleven small liters a second, which can be qualified of severe low water level (see note).

As for the risings, they can be very important taking into account the modest size of the river and its catchment area. The QIX 2 and QIX 5 are worth respectively 15 and 21 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 25 m ³ a second, the QIX 20 of 29 m ³, while the QIX 50 was not calculated being given the insufficiency of the duration of observation to do it validly (see note). Taking into account the extent of their respective basin, these levels of rising are largely higher than those of the Arve for example (QIX 20 of 690 m ³ a second for an area catchment 55 times vaster).

The recorded maximum instantaneous flow with Saint-Genis-Pouilly during this 18 years period, was of 27 m ³ a second on January 13rd, 2004, while the value maximum day laborer was of 20,2 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 not even of a vicennial nature, and thus intended to rather frequently reproduce (the every 12-15 years on average).

Allondon is an abundant river, strongly supplied with strong precipitations of its basin. The Lame of water past in its catchment area is of 730 millimetres annually, which is largely higher than the overall average of France all confused basins, like with the average of the basin of the the Rhone (670 millimetres with Valence and 557 with Beaucaire), but a little lower than the national average Suisse (900 to 950 millimetres), profiting it is true extremely important alpine pluviometry. The specific Flow of the river (or Qsp) reached the high figure of 23,1 liters a second and per square kilometer of basin.

Ecology

Alluvial zone of national importance for Switzerland, the small valley of Allondon is a remarkable natural surface. Composed of a mosaic rich person of very diversified mediums, enjoying in addition a particular climate, this site classified cantonal natural reserve in 1968 is a true lung of greenery. However, of the Pollution S poisons on several occasions affect the river as during the summer 1975 where a toxic discharge in Lion, an affluent of Allondon, poisons the river on several kilometers. In August 2001, a caustic discharge of Soude directly in the river kills several thousands of Poisson S.

Affluents

| url= http://www.fgsp.ch/Rivieres/Allondon/Fiche/Allondon_F.htm | titer=Fiche river: Allondon | auteur=État of Geneva | consulted le= October 18th, 2007 }} ==

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