Lac de Sylans
| Lac de Sylans | ||
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| View of the Lake of Sylans at low tide | ||
| Geographical location | Ain department , France | |
| Tributaries | Charix | |
| Drain | Doye → Suran , Combet → Semine | |
| Location close to the shore | Les Neyrolles | |
| Data | ||
| Coordinates | 46 ° 9 '43 " N , 5 ° 40' 0" E | |
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| Altitude above sea level | 584 m | |
| surface | 0.48 km² | |
| length | 2 km | |
| width | 250 m | |
| volume | 4,800,000 m³ | |
| Maximum depth | 22.0 m | |
| Catchment area | 30.7 km² | |
The Lac de Sylans (German Lake of Sylans ) is located in the Ain department of the Auvergne-Rhône-Alpes region in France . It was created by a landslide and is part of a ravine in the Jura Mountains that runs across its mountain ranges.
geography
The lake is located in the Jura transverse valley Cluse de Nantua , which cuts through the anticlines of the Jura in an east-west direction, about 5 km east of Nantua . It covers the valley floor for a length of 2 km and is enclosed on the north and south sides by wooded steep slopes that rise up to 350 m in height. In the area of the lake, the Cluse de Nantua forms one of the narrowest places, so that the lake only reaches a constant width of 250 m. Most of the lake belongs to the municipality of Le Poizat , which, however, is a few kilometers southeast on the Grande Montagne plateau . A little bit from the west end of the lake belongs to the municipality of Les Neyrolles .
Due to its location on the watershed between Semine and Oignin , the lake only has the Charix brook as a tributary, but due to its location in a karst area , it is assumed that there are underground tributaries that enlarge the topographical catchment area of 30.7 km². A special feature of the lake is the existence of two different drains. The lake water seeps away on the west side in the loose rock of the impounding rock eruption and reappears as the source of the Doye above Les Neyrolles. The amount of runoff caused by this is roughly constant and drains a 4–5 m wide strip of banks in the summer months with less precipitation. In wet periods and especially in winter, this flow rate is insufficient and the excess lake water also flows above ground into the Combet stream on the east side . The runoff to the Combet and the estuary of the Charix meet in the swamp area on the east side, so that depending on the water level, the hydrology cannot always be clearly classified. The lake has no islands.
Emergence
During the Würm glacial period , the Rhône glacier formed a side tongue in the Cluse de Nantua, which helped shape the trough valley , which was several hundred meters wide at the bottom . However, the Lac de Sylans was not formed until the end of the Middle Ages, when a large rock fall occurred at the western end of the lake.
ecology
The average retention time of the water in the lake is given as 210 days, but the uncertainty of this estimate is high, due to the complicated hydrology and the regular changes in volume. In summer there is a clear thermal stratification with a water temperature of up to 23 ° C on the surface, a mixing with the layers below 6 m depth only takes place in March after the ice melts ( meromictic waters ).
The lake water is medium-hard with around 10 ° dH, due to the lime-rich catchment area. The electrical conductivity is 350 µS / cm. Most of the deposits in the lake consist of silt , i.e. H. from mineral sediments of very small particle size.
Flora and fauna
The bank is wooded in the area of the steep slopes, and there is lush vegetation in the area of the former ice works that have been preserved as ruins . A swamp area is at the eastern end of the lake. Various unicellular algae species can be found in the water: in winter especially the genus Gymnodinium helveticum , which belongs to the dinoflagellates , while in summer the species Dinobryon sertularia multiplies strongly and also represents a large proportion. Larger plant species only grow on a small part of the lake area, and their biodiversity is also low. There are pondweeds , Myriophyllum spicatum , stoneworts also, as well as on marshy flat Ostufer mare's tail was observed. Pea mussels also live on the lake bed .
Protection status
The Lac de Sylans has been a site classé since 1909 , i. H. a protected landscape area. Due to the low population density and the absence of large agricultural areas in the catchment area, as well as the disposal of street sewage, there is hardly any risk of pollution or overfertilization.
Economical meaning
There are major road and rail links on both sides of the lake. On the north bank is the departmental road D1084, which leads from Bellegarde-sur-Valserine via Nantua to Pont-d'Ain , as well as the A40 motorway , whose junction at Les Neyrolles is directly on the lake. In the area of the steep slope above the lake, the motorway runs on a stilt viaduct , the Viaduc de Sylans . The Haut-Bugey railway line runs along the narrow south bank with TGV traffic between Geneva and Paris .
Due to its mountainous location, which is shaded by steep slopes, the lake is regularly frozen over in the season from November to March. An entrepreneur from Nantua founded the Sylans ice works in 1865, which harvested the very pure natural ice in winter, stored it and delivered it to customers for cooling purposes during the rest of the year. With the help of the railway line, completed in 1882, the ice works delivered around 300,000 tons of ice per year to Paris. The Société des Glacières de Paris bought the ice works in 1885 and built a 150 m long and 12 m high company building made of masonry stone on the lakeshore, which today still dominates the lake panorama as a ruin. However, the advancing electrification and spread of refrigerators caused the demand for natural ice to collapse again in the decades that followed. In addition, mild winters from 1911 made it difficult to obtain ice, so that it was discontinued in 1917 during the First World War .
Nowadays the lake ensures the drinking water supply of Les Neyrolles.
Web links
Individual evidence
- ↑ a b c d e f g Report on the water quality of the Lac de Sylans 2011 (PDF; 2.5 MB) by the Agence de l'Eau Rhône-Méditerranée et Corse in the EauFrance information system (French).
- ↑ a b Lacs et étangs de France - Le Lac de Sylans (French, accessed January 2014).
- ^ Report on the water quality of the Lac de Sylans 2008 (PDF; 33 MB) by the Ministère de l'Écologie, de l'Énergie, du Développement durable et de l'Aménagement du territoire in the EauFrance information system (French).
- ↑ The Combet 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).
- ↑ 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).
- ↑ Lancement des travaux des glacières de Sylans published on January 29, 2013 in the Tribune Republicaine de Bellegarde (French, accessed January 2014).