Forggensee

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Forggensee
Forggensee from the north;  in the background Tegelberg, Säuling, Thaneller and Tannheimer Berge, Neuschwanstein Castle to the left and Füssen to the right at the foot of the mountains
Forggensee from the north; in the background Tegelberg , Säuling , Thaneller and Tannheimer Berge , Neuschwanstein Castle to the left and Füssen to the right at the foot of the mountains
Location: District of Ostallgäu
Tributaries: Lech , Füssener Ache, Mühlberger Ache
Drain: Lech
Larger places on the shore: Feet
Larger places nearby: Schwangau , Halch , Rieden am Forggensee , Roßhaupten
Forggensee (Bavaria)
Forggensee
Coordinates 47 ° 37 '0 "  N , 10 ° 44' 33"  E Coordinates: 47 ° 37 '0 "  N , 10 ° 44' 33"  E
Data on the structure
Construction time: 1950-1954
Height above valley floor: 37 m
Height above foundation level : 41 m
Height above the river bed : 34.8 m
Height of the structure crown: 785  m above sea level NHN
Building volume: 650,000 m³
Crown length: 320 m
Crown width: 10 m
Slope slope on the air side : 1: 1.5 - 1: 1.75
Slope slope on the water side : 1: 1.75
Data on the reservoir
Altitude (at congestion destination ) 780.5  m above sea level NHN
Water surface 15.2 km²dep1
Reservoir length 8.7 kmdep1
Reservoir width 2.8 kmdep1
Storage space 168 million m³
Catchment area 1594 km²
Design flood : 1 300  m³ / s
Particularities:

Reservoir instead of a historic lake

Forggensee from Kellenspitze.JPG
Forggensee and Füssen from the Kellenspitze (2238 m)

The Forggensee , also known as the Roßhaupten reservoir , is a reservoir through which the Lech flows, near Füssen in Königswinkel in the Bavarian Allgäu . With an area of ​​15.2 km², the lake is the fifth largest lake in Bavaria and the largest reservoir in Germany . It is located in the Ostallgäu district , two thirds of which are in the district of Schwangau . Other neighboring communities are Füssen , Halch , Rieden am Forggensee and Roßhaupten . The lake got its name from the former flooded hamlet Forggen.

Emergence

After the climax of the last ice age, the Lech-Wertach-Vorland glacier, which covered the entire Ostallgäu, gradually melted back from its maximum level at Kaufbeuren , whereby, as in the entire pre-alpine area , at the edge of the glacier tongue in the event of intermittent blockages or renewed growth of the glacier from the ice Masses of debris carried along from the mountains piled up new moraine walls, which are still clearly legible in today's landscape.

Füssener See

Even if the Forggensee, as it is today, is not a natural lake, it is located in a basin that was still filled by a much larger lake after the last Ice Age: When the Lech Glacier continued to melt after the Worm Ice Age , initially formed large dead ice masses , after their melting, lakes formed in the cavities.

North of the Lechfall , dammed up by the ridge of the south wing of the Murnau Mulde (tectonically arranged sediments of the molasses , which are more resistant to erosion than the rocks of the Cretaceous flysch zone to the south ), an up to 60 km² large, at over 790  m above sea level Füssener See , located at NHN , which can be seen as the forerunner of today's Forggensee and most of the smaller pre-Alpine lakes in this area that still exist today. The Alpine foothills were finally free of ice around 14,500 years ago.

Siltation

The resulting lake basins were filled with clay and silt deposits from the glacier melt water in a relatively short time. The Füssener See also silted up more and more, although it also flowed out through the Illasberg Gorge, which the Lech gradually dug through the south wing of the Murnauer Mulde near today's barrage 1 at Roßhaupten . In this gorge, the Lech cuts through the steep layers of the Tertiary Lower Sea Molasse and the Lower Freshwater Molasse ( Tertiary ), from south to north these are the layers of the Deutenhausen Formation, the clay marl layers, the brick layers and especially the Weißach layers the lower freshwater molasse (Illasberg, Zwieselberg, Senkele).

Only the smaller lakes in depressions in the former lake bed remained: Bannwald , Hopfen , Schwansee and Weißensee ; the Alpsee z. B. on the other hand was always an independent lake. In the Lech Valley , a great wild river landscape developed, the Lechauen, whose river arms, gravel banks and wide floodplains were the habitat for a rich fauna and flora ; so the red deer that came down from the mountains wintered in it .

Reservoir

Imposing view of the mountains with a great color of the Forggensee
Forggensee

The first plans for the use of hydropower at Roßhaupten were made at the end of the 19th century. In 1898 the company Siemens & Halske bought the first land in the area of ​​the Lech breakthrough near Roßhaupten and received a concession to build a hydropower plant, which expired in 1907.

In 1910 the Royal Supreme Building Authority published a memorandum on the use of the water power on the Lech , according to which a dam wall with a height of 34 m, a crown length of 140 m and a storage tank with a total volume of 65 million m³ was to be built at Roßhaupten . The First World War and economically difficult post-war years prevented the realization of this project.

The increasing demand for electricity in the inter-war period aroused renewed interest in building a Lech reservoir. A draft from 1936/37 saw a storage target of 784  m above sea level. NHN , i.e. three meters higher than later, and a concrete wall with a built-in power station.

In 1940 Bayerische Wasserkraftwerke AG (BAWAG) was founded to expand the Lech, Untere Isar and the Upper Danube with power plants. Due to the start of the war and the long construction period, the planned start of construction of the Roßhaupten storage facility was postponed. Only the Lech stages 7 to 15 between Landsberg and Schongau could be built between 1940 and 1950 - the smaller power plants could be realized more quickly.

After the end of the Second World War , the Lechspeicher project was resumed. After tough negotiations, the congestion target was set at 781  m above sea level. NHN - the originally planned water level of 784  m above sea level. NHN would have meant larger resettlements of 1500 to 2000 people and, especially in the area around Schwangau, considerable loss of land for agriculture. The Whitsun flood in 1999 gave an impression of this extent , when the lake level on May 22, 1999 was 782.91  m above sea level. NHN was only a good meter lower than the originally planned congestion destination.

Bawag, now only responsible for expanding the Lech barrages, started building the Lech reservoir in 1950. This led to strong protests by the residents who founded a protection community and reached a largely satisfactory agreement with Bawag with the 1952 Schwangau Treaty. For those affected, new farms could either be found nearby or new houses were built. Above all, many of the farmers and their descendants who lived in what is now the Forggensee area can be found in the surrounding communities to this day.

Representation of the lake area on a historical map from 1818

Construction of the dam began in early 1951 after the development measures - including the construction of the new access roads and a residential camp for the up to 1000 workers involved - had been completed. In order to guarantee the tightness of the dam structure, the entire dam and the associated structures were founded directly on rock; For geological reasons, this did not happen directly at the breakthrough of the Lech through the Illass Gorge , as originally planned , but about a kilometer downstream, so that the ecologically valuable gorge was lost. On the lake side, a five meter thick concrete apron was built into the rock up to 20 meters deep. In the spring of 1952, the Lech was dammed on this and diverted through a tunnel that had been built in the meantime. In the remaining two years until completion at the end of 1954, the remaining structures were built and the dam was raised. Most of the building materials were obtained from the reservoir itself.

Forggensee dam from the south aerial view (2019) .jpg
Forggensee dam from the west aerial photo (2019)
Forggensee dam from the north aerial view (2019) .jpg
Forggensee dam from the east aerial photo (2019)
Forgensee Uberlauf.JPG
Flood overflow


Lech-Füssen area in Roman times.

The Roßhaupten barrage was renovated in 2018, which is why the lake was not filled in 2018 (as is usually the case every spring). In 2019 the lake was dammed again.

Preservation of monuments and archeology

A total of 32 inhabited buildings with 256 inhabitants (1950) from the Schwangau villages of Brunnen , Forggen and Deutenhausen , including 16 farms with 800 hectares of usable area east of the Lech were affected by the flooding of Lake Forggen in 1954. On the west bank, the lower Osterreinen on the old street and individual buildings near Dürracker and Füssen were demolished; the Lower Weidachsiedlung near today's Weidach district was completely relocated, 32 families had to leave their houses. Of the affected buildings, only 14 houses from Deutenhausen “survived”: They were bought from Bawag by Theodor Momm , the owner of the spinning mill of the same name in Kaufbeuren, in 1952 , demolished in autumn 1954 and rebuilt in the area by displaced persons. Figures of saints from the Deutenhausen chapel, on the other hand, are now in St. Coloman .

The former episcopal mill, which was moved from Waltenhofen to Forggen in 1644 , was probably the most important building among the stately individual farms, the foundations of which are crumbling on the lake floor.

At the northern end of the lake discovered Dösinger local historian Sigulf Guggenmos (1941-2018) several significant archaeological sites, including traces of Mesolithic hunting stations and a late Celtic and Roman times holocaust site .

A few hundred meters from the current bank, on the former path from Brunnen to Forggen, you will find foundation walls that were cleared in 1974 and the remains of brick from a Roman villa rustica . Such estates supplied travelers on the Roman roads. In the opinion of the Bavarian State Office for the Preservation of Monuments , a solid road embankment that is still clearly recognizable there and is oriented towards the landmarks Auerberg in the north and Säuling in the south could be a forgotten Roman road, perhaps a connection from the Roman settlement of Tegelberg to the Via Claudia Augusta and her trading post at Osterreinen . It is therefore possible to follow an additional Roman road from Pinswang through the Alpsee saddle and over the Roman settlement on Tegelberg, which is used for seasonal reasons .

use

The Forggensee is used on the one hand to generate electricity directly and also as a so-called top storage tank for the increase in low water levels for the hydropower plants downstream, and on the other hand, the lake is important for flood regulation ( flood protection ) on the Lech after the onset of snowmelt. Mainly in summer it is also used for local recreation.

Power generation

The two Kaplan turbines of the storage power station have their 30 MVA - screen generators along a rated output of 45.5 MW m at a drop height of 35.4 and a flow rate of 75 m³ / s. The average annual working capacity is 152.6 GWh.

The Uniper power plants GmbH (FM) has become the operator of the power plants. The power plant itself is usually unoccupied; it is controlled via the central control room in Landshut .

The water supplied to the power plant, up to 150 m³ / s, is taken from the Forggensee just above the foot of the dam through an inlet structure on the north slope with three openings, each 8.25 meters high and three meters wide, and flows over a length of 325 meters through an 8 , 35 meter wide circular headrace tunnel through a Y-pipe in two pipes with a diameter of 4.5 meters each. From there it is fed into the two inlet spirals of the turbines and back into the Lech.

The Hydropower Information Center, which is part of the Auerbergland Museum Association, is located in the premises of the Roßhaupten power plant and informs visitors about the generation of regenerative energy from hydropower of the Lech and about the relationships between the river, the environment and the residents.

Flood protection

As a result of the floods since 1999, the state of Bavaria developed several programs for protection against flooding . For the Forggensee, a general lowering of the storage target by half a meter (from 781  m above sea level to 780.20 -  780.7  m above sea level ) was therefore determined from 2005 ; 7.5 million m³ of additional catchment reserves for floods can be kept ready. In addition, the lake level can now be lowered as a precaution in order to be able to better absorb the high water peaks. In 2005 a new flood relief system was installed.

For communities with flat bank areas - this particularly includes Schwangau - renovation measures were necessary due to the lowering of the normal water level. The existing port facilities of water sports clubs had to be connected to the "new Forggensee" with canals . Ground monuments that had previously been protected under water appeared and needed protection against rapid weathering. In the area of ​​Horn and Waltenhofen, there are wider pebble beaches up to the lake.

Recreation

In winter the lake is dry and the bottom is accessible. Due to this possibility, ground plans of buildings are still visible in some places , which were then demolished for the construction of the Forggensee, and traces of old roads, even the Roman road Via Claudia Augusta , then emerge from the waters of the lake.

In summer, when the traffic jams from June 1st to October 15th, the lake is also used for recreational purposes. It offers opportunities for all water sports, so there are several sailing schools. Forggensee shipping has existed since 1955.

In the south of the lake near Füssen, on August 25, 1998, the 153rd birthday of King Ludwig , the foundation stone was laid for the Richard-Wagner festival theater , which was then called the Neuschwanstein Musical Theater, on a newly built 45,000 m² plot of land in the Forggensee -Festspielhaus in Bayreuth is modeled after . The opening took place on April 7, 2000 with the world premiere of the musical Ludwig II - Longing for Paradise .

Schwangau - Forggensee Abstau 020414 - Forggen v NW 01.JPG
Remnants of the hamlet Forggen in the dammed Forggensee
Forggensee low level 2014 (9) .JPG
Tiefentalbrücke on the former federal road
ViaClaudiaForggensee.jpg
Via Claudia Augusta between Rieden and Roßhaupten
Boat landing stage Füssen.jpg
Boat mooring feet for the Forggensee shipping company
Musical Theater Neuschwanstein View from the terrace 2003.jpg
Musical theater Neuschwanstein; view

Gravel mining

The Forggensee is used for gravel mining, which is only possible in winter when the lake is drained, but then very easily in open-cast mining. It is listed in the Allgäu regional plan as the only priority area for gravel mining in southern Ostallgäu.

Hydrology

At 1596.66 km², the Forggensee has the largest catchment area of ​​all Bavarian lakes, and with 69.7 m³ / s it receives the most water. This enormous amount of water is also the reason why the Füssener See was on the one hand very quickly filled with sediments after the last ice age and on the other hand the drainage at the Illas Gorge deepened so that the lake finally drained completely. Otherwise, instead of the Forggensee, there would probably be a Zungenbeckensee similar to the other pre-Alpine lakes .

Water data
Conductivity: 230-280 µS / cm
pH value : 7.1 (late autumn) - 8.8 (summer)
Oxygen content: 7.4-8.8 µg / L
Phosphorus content normal: 10-20 µg / L
Extreme phosphorus content: 60 μg / l (early summer)
Ammonium nitrogen: 20-90 µg / L

Water properties

The Forggensee belongs to the type of the calcareous pre-alpine lake. According to the chemical and biological data, the Forggensee can be classified as mesotrophic to slightly eutrophic . The visibility depth in spring is only around 0.8 m due to the mineral suspended matter after the damming, while it is up to 6 m in summer and autumn.

Inflow and outflow

The largest tributary is the Lech, which with 1,423.62 km² also drains almost nine tenths of the entire catchment area. With an average discharge of 65.7 m³ / s, it supplies most of the water flowing into the Forggensee; only the Füssener Ache (mouth north of the musical theater) with 1.53 m³ / s and the Mühlberger Ache (mouth for wells ) with 1.26 m³ / s.

The location of the Forggensee at the outflow of the Lech from the mountains causes very strong fluctuations in the Lech level; During the flood of 1910 a maximum discharge of 915 m³ / s was measured, during the Whitsun flood in 1999 it was 1115 m³ / s, in August 2005 even 1262 m³ / s, and thus almost 20 times the mean discharge. Although the Forggensee has been drained as a precautionary measure since 2005 to prevent flooding, exceeding the highest storage target of 782  m above sea level is a must. NHN so not completely avoidable.

fauna and Flora

In the middle of the picture the formerly independent Illasbergsee, today part of the Forggensees. At the top right the dam wall with Lech.

The district fishing association Füssen manages the fishing of the Forggen lake. The annual stocking with pike , carp , pikeperch , rainbow trout and lake trout makes the Forggensee an interesting fishing water. There are also grayling , bream , perch and tench . The remaining lake, which shrank to an area of ​​approx. 3.2 km² in winter, offers the fish population the necessary wintering opportunity. In the past, the Forggensee repeatedly caused a sensation by catching large pike and bream .

The Forggensee is a breeding ground for water birds and a resting place for many migratory birds .

Larger aquatic plants cannot survive during the winter months due to the strong fluctuations in the water level and the almost complete drying of the lake bed. only on the shallow, gravelly bank areas in the southern part of the lake is sparse vegetation with reeds and willows to be observed. The Illasbergsee (a small annex of the Forggen lake, east of the outflow in the north) shrinks when it subsides in the winter half-year to a pond-like body of water surrounded by reed beds.

Panoramas

Northern end of the Forggensee with a view of the Illasberg Gorge
Southern end of the Forggen lake with a view of Füssen
Aerial view of Lake Forggensee at low tide from the southeast (March 2020)

See also

Individual evidence

  1. Christian Rost: The Forggensee stays dry this summer. Süddeutsche Zeitung, April 30, 2018, accessed on May 26, 2018 .
  2. ^ Roßhaupten Dam project - information on the renewal of the dam seal. Uniper , April 2, 2019, accessed April 30, 2019 .
  3. ^ Official register of places for Bavaria, edited on the basis of the census of September 13, 1950, Munich, 1952, column 1288
  4. Armin Guggenmos, Birgit Gehlen: Obituary S Guggenmos BA . In: Bavarian Archeology . ( academia.edu [accessed October 30, 2019]).
  5. ^ Auerbergland eV: Hydropower Information Center , accessed on April 16, 2014
  6. fuessen.de: Boat tour on the Forggensee with the Forggensee shipping
  7. Katharina Knoll: The decision to mine gravel has been made. In: Kreisbote Füssen. February 7, 2020, accessed August 3, 2020 .

literature

  • Peter Franke, Wolfgang Frey: Dams in the Federal Republic of Germany . DNK - DVWK 1987, ISBN 3-926520-00-0
  • Josef Frohnholzer: The Roßhaupten reservoir as the main link for the master plan for the Lech . Water management 43, issue 7 + 8, 1953
  • Georg Grieser, Peter Nasemann, Magnus Peresson: The Forggensee - Images from a sunken world . Schwangau, 2004
  • LA Haimerl: The Roßhaupten storage power plant . Schweizerische Bauzeitung , issue 10 + 11, 1961
  • Bernhard Kalusa: The Forggensee is 50 years old . WasserWirtschaft , issue 8/2004.
  • Hermann Schiechtl: Measuring and control devices in the Roßhaupten dam to assess the safety of the dam . XIV. ICOLD Congress Rio de Janeiro 1982
  • F. Driver: measurements and observations in the Roßhaupten dam . VI. ICOLD Congress New York 1958
  • Rupert Zettl: Lechauf-lechab . Wißner-Verlag 2002, ISBN 3-89639-316-2
  • E. Pfeuffer: “The untamed Lech. A lost landscape in pictures ”. Wißner-Verlag Augsburg 2011 ISBN 978-3-89639-820-8

Web links

Commons : Forggensee  - collection of images, videos and audio files