Lac de Nantua
| Lac de Nantua | ||
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| View of the lake and Nantua | ||
| Geographical location | Ain department , France | |
| Tributaries | Merloz , Doye | |
| Drain | Bras du Lac | |
| Places on the shore | Nantua , Montréal-la-Cluse | |
| Location close to the shore | Oyonnax | |
| Data | ||
| Coordinates | 46 ° 9 '37 " N , 5 ° 35' 24" E | |
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| Altitude above sea level | 475 m | |
| surface | 1.33 km² | |
| length | 2.5 km | |
| width | 650 m | |
| volume | 40,000,000 m³ | |
| Maximum depth | 42 m | |
The Lac de Nantua (German Lake of Nantua ) is located in the Ain department of the Auvergne-Rhône-Alpes region in France . It is of Ice Age origin and part of a gorge in the Jura Mountains that runs across its mountain ranges.
geography
The lake has a length of 2.5 km and an approximately constant width of 650 m. It lies at the northern foot of the Montagne de Chamoise and forms the western exit of the Jura transverse valley Cluse de Nantua , which cuts through the anticlines of the Jura in an east-west direction. The lake belongs entirely to the municipality of Nantua, which is located directly on the eastern bank. On the west bank are Montréal-la-Cluse and the small community of Port .
The two main above-ground tributaries are the Merloz and Doye streams . These drain a section of the Cluse de Nantua, which is only a few kilometers long, as the watershed to the Semine runs above Les Neyrolles . North of Port, the short Bras du Lac leads the lake's water to the Oignin River . Due to its location in the middle of a karst region , underground inflows and outflows also contribute to the exchange of water. On the north and south sides of the lake, wooded steep slopes rise up to 300 m, which are criss-crossed by striking rock faces. The lake has no islands.
Emergence
During the Würm glacial period , the Rhône glacier formed a side tongue in the Cluse de Nantua, the terminal moraine of which protruded into the Ange and Oignin valleys . After the ice melted, a typical tongue basin lake remained, the water level of which was increased by the terminal moraines, which are up to 90 m thick. Its extension was many times that of today's Lac de Nantua and reached as far as Nurieux , Montréal-la-Cluse and Saint-Martin-du-Frêne .
In 1856, the municipal administration of Nantua had the Bras du Lac straightened and the lake level lowered by about 1 m in order to avoid flooding and gain marshy areas as additional land.
ecology
The average length of time the water remains in the lake is estimated at 251 days, which is a significantly faster water exchange compared to the neighboring lakes of Annecy and Le Bourget . In spite of this, the discharge of sewage finally led to severe nutrient pollution ( eutrophication ) in the early 1970s , from which the lake is only slowly recovering. In summer there is a clear thermal stratification with a water temperature of up to 25 ° C on the surface ( meromictic water ), a mixing with the layers below 10 m depth only takes place in winter. The lake water is medium-hard with around 10 ° dH, due to the lime-rich catchment area. The electrical conductivity is 390 µS / cm. Most of the deposits in the lake consist of silt , i.e. H. from mineral sediments of very small particle size.
Measures to protect
As a reaction to the high nutrient load and the resulting lack of oxygen, especially in deeper layers, a sewage network was put into operation in 1972. This collects the wastewater from the two communities on the lake shore (Port, Nantua) and from Les Neyrolles above the lake and feeds it to a specially built sewage treatment plant at the end of the Bras du Lac . In order to accelerate the recovery of the lake, oxygen was introduced into the deep layers (35 m depth) in a test facility . For this purpose, 15, 51 and 60 tons of oxygen were dissolved in the water in the summers of 1976, 1977 and 1978 using circulation pumps. However, a series of measurements during the intervention in 1978 did not show the expected increase in the oxygen content, so that this introduction was not continued in the following years. It was assumed that both the stimulated microfauna and chemical reactions with the sedimentary rocks immediately used up the oxygen introduced.
The situation of the lake has improved, especially in recent years, and the lack of oxygen at the end of summer stagnation below 10 m depth was less pronounced.
Flora and fauna
The bank is wooded in the area of the steep slopes, but only as far as the traffic routes there allow. There are also completely redesigned sections such as the sea walls and a beach in Nantua. There is a swamp area with reeds in Port. The biomass consists essentially of phytoplankton , with Dinobryon divergent in the upper water layers and Burgundy algae predominate in the lower layers . The pond roses and large mermaid are larger plants . The bottom of the lake is mainly inhabited by mud tubers and pea mussels . The fish population is diverse and includes perch , pike , lake trout and carp .
Protection status
The Lac de Nantua has been a site classé since 1936 , i. H. a protected landscape area. All construction and demolition measures are therefore under state supervision and installations that can negatively affect the appearance, such as billboards or above-ground power lines, are prohibited.
Attractions
On the south bank on a peninsula created especially for this purpose, there is a memorial to commemorate the victims of the deportations from the Ain ( Mémorial aux Déportés de l'Ain ). A plaque commemorates 595 people from the Ain department who were deported to concentration camps for political reasons between 1940 and 1944, i.e. during the Vichy regime and the German occupation, and who died or were executed there. Another plaque is dedicated to the children of Izieu . The memorial was commissioned in 1947 by citizens of Nantua who had survived the deportations, and the artist Louis Leygue , himself a deportee, was entrusted with the execution. He created a sculpture that shows a lying, emaciated man under a large block of stone weighing around 70 tons. A recess in the middle of the block sheds light on the figure. The memorial was inaugurated in November 1949.
Economical meaning
The lake can be reached via the departmental road D1084, which leads from Bellegarde-sur-Valserine via Nantua to Pont-d'Ain , and via the A40 motorway , which has a connection to the D1084 a few kilometers east and west. In the area of the lake, the motorway runs through the Chamoise tunnel, but the Viaduc de Nantua motorway bridge leading to the tunnel portal has been clearly visible in the lake panorama behind Nantua since 1986.
The city of Nantua has geared its tourism concept to the lake and its scenic beauty. Various water sports such as sailing, canoeing or water skiing can be practiced. The local fishing club offers daily and weekly fishing licenses. At the southern tip there is a bathing establishment with a beach on the lake shore and a campsite.
Web links
Individual evidence
- ↑ a b Data on Lac de Nantua in the EauFrance information system (French, accessed in January 2014).
- ↑ a b c d e Synthèse des retours d'expériences des projets de restauration sur le plans d'eau… (PDF; 16MB) ( Memento of the original from June 16, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and still Not checked. Please check the original and archive link according to the instructions and then remove this notice. of the Agence de l'Eau Rhône-Méditerranée et Corse in the EauFrance information system. Pp. 201-202 (French).
- ↑ The Bras du Lac on sandre.eaufrance.fr (French, accessed January 2014).
- ↑ Géologie du Bugey chp. 4: Le nord du Bugey (PDF; 3.48 MB) by J. Beauchamp (French, accessed January 2014).
- ↑ Plan for the coordination of concepts and management of the Lac de Nantua prepared by CAUE de l'Ain ( Memento of the original from January 16, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , P. 265 (French, accessed January 2014).
- ↑ a b Report on the water quality of Lac de Nantua 2010 (PDF; 2.14 MB) by the Agence de l'Eau Rhône-Méditerranée et Corse in the EauFrance information system (French).
- ^ J. Feuillade: Caractérisation et essais de restauration d'un écosystème dégradé: le lac de Nantua . INRA, 1985, ISBN 2-85340-638-5 , pp. 165 ( online ).
- ↑ List of sites and monuments classés in the Ain department (PDF; 0.5 MB) on the Services de l'État dans l'Ain website (French).
- ↑ Monument des Déportés de Nantua ( Memento des Originals of December 26, 2014 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. on the Portraits et monuments de l'Ain website (French, accessed January 2014).
- ↑ Histoire du mémorial on the website Mémoire de la Déportation dans l'Ain (1939–1945) (French, accessed January 2014).
