Aire (Swiss stone pine)
| Aire | ||
 The Aire at Lully |
||
| Data | ||
| Water code | FR : V0240560 , CH : 91 | |
| location | France , Switzerland | |
| River system | Swiss stone pine | |
| Drain over | Arve → Rhone → Mediterranean | |
| source | in the municipality of Andilly 46 ° 4 ′ 39 ″ N , 6 ° 5 ′ 33 ″ E |
|
| Source height | approx. 750 m | |
| muzzle | in Geneva, Switzerland, in the Arve Coordinates: 46 ° 11 '57 " N , 6 ° 7' 43" E ; CH1903: 498 881 / 117258 46 ° 11 '57 " N , 6 ° 7' 43" O |
|
| Mouth height | approx. 370 m | |
| Height difference | approx. 380 m | |
| Bottom slope | approx. 35 ‰ | |
| length | 11 km or 18 km | |
| Catchment area | 95.1 km² | |
| Big cities | Geneva | |
| Small towns | Saint-Julien-en-Genevois | |
The Aire is a left tributary of the Arve in the Geneva basin. It is created by the confluence of several streams in France , at the foot of the Salève mountain in the Haute-Savoie department . After just a few kilometers, the course of the river crosses the Swiss border and flows into the Arve within the city of Geneva , just a few hundred meters above the confluence of the Arve and Rhone . Both the course of the Aire and its hydrological properties are largely determined by human intervention. Together with its tributary Drize, the Aire drains a catchment area of 95.1 km², of which 63.9 km² is on Swiss soil.
The Aire is considered to be the most severely impaired river in the canton of Geneva with very poor water quality and is therefore the subject of several renaturation measures and better control of water inputs.
geography
The Aire combines a system of several streams that drain the slopes of Mont Salève and Mont Sion towards the Rhone. It touches the places Feigères and Neydens and then flows around the place Saint-Julien-en-Genevois on its south and west side. On Swiss territory, the Bernex plateau , which rises about 100 m from the Geneva basin, prevents a direct runoff into the Rhone. This plateau extends over Onex to Petit-Lancy , so that the Aire flows north-east towards the Arve valley, in the opposite direction to the Rhone, which flows on the other side of the plateau in a south-westerly direction.
Course and structures
The Aire, formed by the various source streams in the south of the village of Saint-Julien, initially runs in a westerly direction and then swings northwards towards the state border with Switzerland, which it crosses at Thairy . In Switzerland it flows further northwards past Certoux and Lully until it meets the Bernex plateau. From then on, it runs in a north-easterly direction and it crosses the municipalities of Confignon , Onex and Lancy . Between Certoux and the border between the municipalities of Confignon and Onex, the Aire was diked and canalized over a length of 4 km in the first half of the 20th century. In the period from 2003 to 2014, the canton of Geneva is carrying out extensive renaturation measures, which are intended to restore the Aire river bed in this area as naturally as possible. In the municipal areas of the Geneva suburbs Onex and Lancy, it has kept its natural river bed up to the Pont-Rouge bridge , from where it is fed into the Arve in an underground canal. This canal reaches the Arve below the Saint-Georges bridge.
The Aire valley basin is heavily urbanized in both France and Switzerland. The infrastructure of the motorways A40 , A41 , A1 and other roads shape the upper valley of the Aire and contribute to the entry of water. From Confignon it flows through the suburbs of Geneva with buildings reaching to the banks. There are vineyards on the slopes west of the Aire near Bernex, and the plain east of the Aire is used intensively for agriculture. The situation in which a river that has been determined by rainfall crosses under a district posed the risk of flooding. Since 1987, a 2.1 km long flood tunnel has been branching off in the area of the hamlet of Les Charrotons in the municipality of Confignon near the bridge des chemin du marais , which pierces the Onex plateau and flows directly into the Rhone.
In the area between Certoux and Lully, underground water veins run through the permeable gravel deposits and absorb some of the water from the Aire. The water veins only reach a depth of a few meters, so that they come to the surface again with the further gradient of the river below Lully and feed the water back to the Aire. As a result, the Aire between Certoux and Lully falls dry during periods of low precipitation and is not registered as having water all year round in this section.
Tributaries
South of Saint-Julien-en-Genevois, a complicated system of various streams joins the Aire. The main streams are (from east to west) the Arande , the Ruisseau de Ternier , the Nant de la Folle (also called Nant de Feigères ) and the Grand Nant (also called Nant d'Ogny ). The French river database classifies the source of the Nant de la Folle as the source of the Aire, which results in a total length of 18 km for the Aire with the Grand Nant as the left and the Ruisseau de Ternier as the right tributary. The Swiss cantonal authorities, on the other hand, only define the beginning of the Aire at the confluence of the source streams and assume a river length of 11 km. The lower course in Switzerland is 9 km long and the Lissole , Voiret and Drize flow into it on the right . Lissole and Drize are piped underground in the area of the mouth. The cantonal authorities catalog the Drize as an independent river, so the information in this article only relates to the Aire above the Drize tributary. Without the entry of the Drize, the catchment area of the Aire is 67.7 km².
history
The current course of the Aire and the sediment layers in the tributary area are relatively young and formed during the last Ice Age ( Würm Ice Age ). After the Rhone Glacier retreated around 20,000 years ago, a lake formed in the area of the Aire, the outflow of which was blocked by the remains of the Rhone Glacier in the area of the Grand Lancy. This explains the occurrence of a top layer of fine sediments above the glacial gravel deposits.
Straightening
Between 1921 and 1936, land consolidations and basic work on draining the arable land in the plain through which the Aire flows. In this context, corrections were made to the course of the Aire river throughout Switzerland, and the sections between Lully and Les Charrotons in particular were canalised. The section in the Geneva urban area between Pont-Rouge and the estuary was canalized in 1940 and built over in the period 1964–1970. Today the Voie Centrale , the connection between the A1 motorway and Geneva city center, runs along the underground canal . In 1987 the flood tunnel to the Rhone was put into operation and renovated in 2012 to increase its capacity to 50 m 3 / s.
After the Grand Council of the Canton of Geneva had decided on an extensive renaturation program for the Geneva rivers in 1999, it passed a first law in 2001 that restored a natural river bed to the 600 m long section of the Aire between Pont des Marais and Pont du Centenaire . This was followed by two more laws on renaturation work with a total volume of around 50 million Swiss francs, which by 2014 will make the entire area between the state border and Onex natural again.
Sewage treatment plants
In the course of urbanization, sewage treatment plants were built in Neydens, Grossaz , Les Sorbiers (municipality of Feigères), Saint-Julien-en-Genevois and Confignon, which discharged or still discharges their treated wastewater into the Aire. However, since the Aire has only a small natural runoff, the discharges from the sewage treatment plants represent the majority of the runoff in times of low rainfall and have a significant impact on the water quality. The Saint-Julien and Confignon sewage treatment plants were therefore connected to the central Geneva sewage treatment plant in Aïre (municipality of Vernier ) in 2001, which releases its wastewater to the much more stable and larger runoff regime of the Rhone. Sorbiers is also to be connected to that of Aïre, while Grossaz and Neydens were merged and modernized in 2003. After these changes, around 15% of the sewage networks on the Swiss side still function according to the mixed system , each of which requires a rain overflow (into the Aire).
In addition to wastewater from the sewage treatment plants that has now largely been diverted into the Rhone, there are still uncontrolled or diffuse discharges. These are in particular the approximately 40 km long drainage of the neighboring fields and vineyards as well as the rainwater discharges from industrial areas in the area of the municipality of Plan-les-Ouates . In the rural structured area of the Aire tributaries there are still around 1400 inhabitants who are not connected to the sewer system but use septic tanks.
Flood
The strongest recent floods occurred on November 10, 1976, January 28, 1979 and 14/15. November 2002 and flooded parts of Lully. The first two caused the construction of the flood tunnel.
Hydrology
The flow regime of the Aire is a rain regime with strongly fluctuating water levels. Floods can occur all year round with strong thunderstorms or long-lasting rainfall. The adjacent Mont Salève is not high enough to store precipitation as snow for months. Snowfall in the Geneva Basin can, however, increase the amount of runoff in the event that the thaw is accompanied by heavy rainfall. The extreme floods of 1976 and 1979 were caused in this way. The increasing soil sealing in the catchment area strengthens the direct relationship between rainfall and runoff.
Measuring devices for the flow rate are located in Thairy in front of the state border with Switzerland, in front of the discharge into the flood tunnel and on the Pont-Rouge in front of the start of the covered section. Average flow rates of 650 l / s, 800 l / s and 900 l / s are measured at these three points. The 182-day median is only about half as large (e.g. 400 l / s before the branch of the flood tunnel). The values set for a 10-year flood are two orders of magnitude higher and are 45 m 3 / s, 55 m 3 / s and 32 m 3 / s at the three points. The effect of the flood tunnel can now be seen here, which can divert up to 50 m 3 / s into the Rhone and keeps the peak values for the flow rate at the Pont-Rouge low.
environment
The Aire environment was classified as poor at the end of the 20th century in terms of biodiversity and the size and quality of the natural retreats. Initially, only a retention basin for alluvial material at Certoux, which had to be cleaned regularly due to its function, and a natural private property la réserve des Bossenailles , which belongs to the WWF Geneva, existed as retreat areas near the river . The renaturation measures are intended to improve this situation considerably, but as of 2012 it is still too early to fully assess the new environmental situation.
flora
On the banks of the Aire, instead of the flora typical of wetlands, pioneer plants are observed. The worm lettuce , blue gauchheil , the low crow's foot and the poisonous spotted hemlock are named as characteristic plants. A subspecies of the spherical thistle, which is rare in Switzerland, is also found on the banks of the Aire.
fauna
Before the intervention in the course of the river, trout , grayling and gudgeon populated the waters of the Aire in large numbers. Today, however, minnow , chub , brook loach and, occasionally, trout can still be seen on the upper reaches. Fishing has been banned since 1982 for health reasons. Migration between the Aire and the Arve is not possible because of the underground section in front of the Aire estuary. Further obstacles to migration in the course of the Aire were or will be removed by the renaturation measures.
Of the rest of the animal world, only widespread species are observed in the area of the aire, including the native sea frog , the wall lizard attracted by the straightening structures , and the birds and small mammals native to the farmland. The hope is expressed that the renaturation measures will restore a population of river-related species such as. B. enable the kingfisher .
Water quality
The discharge of wastewater from sewage treatment plants, untreated rainwater and surface water contaminated with residues from agriculture impair the water quality of the Aire. Especially in the summer months, when the natural flow rate is small, limit values are exceeded. The physiochemical load from wastewater from sewage treatment plants, especially ammonium, dissolved organic carbon and BOD 5 , has now been significantly reduced. There are still high levels of pollution from fertilizers, pesticides, some metals and E. Coli bacteria.
Web links
- Water quality and map of the watercourses in the canton of Geneva
- Geo-information portal of the canton of Geneva, watercourses
- The renaturation project of the Aire wins the landscape award of the Council of Europe
Individual evidence
- ↑ a b IGN maps on geoportail.gouv.fr
- ↑ a b c d e archive link ( Memento from March 4, 2016 in the Internet Archive )
- ↑ a b Waters FR / V0240560 on sandre.eaufrance.fr
- ↑ a b c d e f g Direction Générale de l'Eau: Fiche rivière N ° 3: L'Aire (2e édition) available on ge.ch
- ↑ J. Mouron, Dérivation des eaux de crues de l'Aire (PDF file; 365 kB), Int. Ass. Of Hydr. Systems No. 194 (1990)
- ^ A b Tribune de Genève, Pour l'Aire, ils passent quatre mois sous terre ( Memento of August 26, 2014 in the Internet Archive ), article of January 29, 2012
- ↑ Archive link ( Memento from August 26, 2014 in the Internet Archive )
- ↑ Archive link ( Memento from August 26, 2014 in the Internet Archive )
- ↑ Direction Générale d'Eau: L'Aire et ses affluents, Etat 2016 et évolution depuis 1998