Glonn (Amper)

from Wikipedia, the free encyclopedia
Glonn
The Glonn near Odelzhausen, Taxa district, in March 2004

The Glonn near Odelzhausen , Taxa district, in March 2004

Data
Water code EN : 1648
location Upper Bavaria , Germany
River system Danube
Drain over Amper  → Isar  → Danube  → Black Sea
source at Mittelstetten
48 ° 14 ′ 52 ″  N , 11 ° 6 ′ 41 ″  E
Source height approx.  525  m
muzzle near Allershausen in the Amper coordinates: 48 ° 25 '59 "  N , 11 ° 36' 14"  E 48 ° 25 '59 "  N , 11 ° 36' 14"  E
Mouth height approx.  440  m
Height difference approx. 85 m
Bottom slope approx. 1.7 ‰
length 50.4 km
Catchment area 405 km²
Discharge at the Hohenkammer
A Eo gauge : 390 km².
Location: 6.4 km above the mouth 		NNQ (03/06/1948)
MNQ 1936–2006
MQ 1936–2006
Mq 1936–2006
 MHQ 1936–2006
HHQ (05/31/1940) 		460 l / s
1.32 m³ / s
3.28 m³ / s
8.4 l / (s km²)
 46 m³ / s
180 m³ / s

The Glonn is about 50 kilometers long, left tributary of the Amper in Upper Bavaria . In contrast to the Glonn (Mangfall) , this Glonn is also called the Northern Glonn .

Origin of name

The river takes its name from the Celtic: "Glanos", which means pure and shiny, or "glana", which means something like "pure, holy". The Romans adopted this name. In documents around the year 770 the river was called "Clana".

landscape

The Glonn flows through the Danube-Isar hill country in a Mulde valley . As a regulated river, the Glonn flows largely without meanders and with isolated oxbow lakes. Adjacent meadows and fields are intensively farmed. One consequence of this is that ecologically relevant guide values ​​for nutrient inputs such as nitrate and phosphate are exceeded . Sufficiently broad bank margins are mostly missing and oxbow lakes only exist in isolated cases. Partly there are landscape and nature conservation areas, such as B. the Weichser Moos and at Petershausen .

and display information about the image
Heron in the Glonntal near Asbach (Petershausen)

course

It rises south-east of Mittelstetten in the Fürstenfeldbruck district , in Wenigfeld (approx. 525 m above sea level ). The water of the nine springs that give the Glonn its origin emerges from the earth at the foot of a valley. Four springs arise in a small wood next to the road, the small stream pours into a pond, which is fed by the other 5 springs. The water of the springs is slightly red in color. When it comes into contact with oxygen, the iron contained in the water oxidizes and turns the earth rust-red.

The Glonn flows 39 kilometers through the district of Dachau , in the direction from west to east, and flows with two arms into the Amper as its most important tributary (approx. 440 m above sea level ) at the church of St. Joseph in Allershausen near Freising .

The slope of the Glonn is therefore around 85 m. The Glonntal has an average width of 1 - 1.5 km.

Discharge values and levels at Hohenkammer : MNQ 1.32 m 3 / s, MQ 3.28 m 3 / s and HQ 180 m 3 / s.

Character and environment

The 50.4 kilometer long Glonn flows through an agriculturally used area in the triangle between Augsburg , Freising and Dachau . The Glonn flows calmly through a naturally fertile valley in the tertiary hill country . With normal water flow in its trapezoidal bed, the water level of the mostly 12 m wide Glonn is approx. 1 - 1.5 m below the terrain. The Glonn flows through the landscape monotonously without any meander. The banks are in parts accompanied by a narrow wooded border or individual trees, the adjoining areas are characterized by agricultural use with the exception of a few hedges and groups of trees. Even more monotonous and barely visible, many side streams of the Glonn flow through the landscape.

Today the Glonn is a canal-like channel that is dammed in many places by weirs. The bottom consists partly of sandy-gravelly substrate, but in flow-calmed sections there are larger mud deposits. Near-natural habitats are only available in a few sub-areas.

Over time, the near-natural habitats, such as the original floodplains, have shrunk to small, valuable remnants. In 1973 the Glonn valley was designated as a landscape protection area. The most beautiful and last remnants of its alluvial forests, litter meadows and fen areas can be found near Weichs and Egenburg. In the core area of ​​the Weichser Moos near Weichs, the peat layer is still two meters deep, at the northern edge it is 70 centimeters.

The diversity of the landscape, which for a long time was regarded as wasteland, is enormous: wet and humid meadows alternate with tall herbaceous meadows , willows and willow bushes and sedge meadows . The ditches and littered meadows mark the area as a rural cultural landscape. For more than 40 years, large parts of the Glonn Valley have been protected in order to preserve and restore the natural area and to make it accessible as a recreational area.

Water quality

The Glonn is a heavily polluted nutrient-rich river. In addition to the pollution from the drains of 31 municipal sewage treatment plants, which are discharged directly or through the side streams, the water quality is also impaired by the discharge of domestic wastewater, mixed water relief and diffuse inputs, especially from agriculture. Due to the numerous non-natural discharges, the ability for biological self-cleaning is overstrained in most streams.

Some of the source streams of the Glonn are still very lightly polluted. From the first sewage treatment plant outflow in Mittelstetten to the confluence with the Amper, the Glonn is critically polluted and therefore belongs to water quality class II - III. Since 2001 no water quality map of the Glonn has been drawn up by the water management authorities in Munich or Freising.

The scientist Marion Immig examined the water quality of the upper Glonn in 2018. The result: the ecological condition of the river is unsatisfactory, the goals of an EU protection directive cannot be achieved in the medium term.

Use and regulation

Historical and current regulation, as well as use

Between 1919 and 1924, the Glonn was a largely regulated river with no dynamic development potential (so-called dynamic river system ). The straightening of the river leads to a deep digging of the Glonn with an impact on the water table .

Numerous barrages also regulate the river. In many places there are drainage channels that are used or have been used by mills, electricity generation plants or wood sawmills. The mills that are still in operation today include (from the source to the mouth): Egenburger Mühle, Vogacher Mühle, Furthmühle (first mill on the Glonn, mentioned in 1165, now a technical museum), Oberhandenzhofer Mühle, Arnbacher Mühle and Obermoosmühle. A large part of the original, historic mills is still used today to generate electricity.

With the construction of these mills, humans first intervened in the river's ecosystem. Economic use began around 1300 when the first mills on the Glonn were built. Over time, the number increased to 24 mills. Today there are still 13 mills, mainly for power generation, on the Glonn. In order to use the hydropower, the river had to be tamed. A constant amount of water, a favorable current and a flood overflow were important. After the water had driven the mill wheels for the grinding or sawmills, it flowed quickly in a deeply buried bed in the so-called mill shot. As can be seen on old maps, the water then spread out like a lake and calmed down again.

Silting up of the Glonn as a trigger for regulation

Almost all of the Glonntal suffered from severe swamping, caused by the numerous mills and engines that were lined up in an almost uninterrupted chain of jams. The dams kept the Glonn water level almost at ground level, so that the adjoining valley floors were deprived of any receiving water for the necessary drainage. The inadequate flow conditions of the old weir and grinding systems and the completely overgrown Glonnbett led to damage in the valley floor even with a small flood. So the valley meadows only produced low yields and poor quality forage. Many meadows almost exclusively bore sour grasses, moss and other marsh plants and so-called weeds, so that they could only be used for litter. Since the water from the Glonn flowed far too slowly through the dams, another consequence was the reduced transport of bed load. This led to a flooding, which also contributed to the waterlogging of the meadows. For this reason, a regulation of the Glonn was sought as early as the 19th century.

River regulation and straightening project

Correction of the Glonn began in 1919 and was completed in 1924. It was carried out on a cooperative basis by the cultural offices in Munich and Ingolstadt. One of the aims of this measure was to drain the valley floor and thus create fertile meadows for agriculture. This was done by deepening the river bed to 2 to 2.5 m; The aim was to lower the water table by around 50 cm. In addition, the water level at the mills was lowered by an average of 90 cm in order to reduce the risk of flooding. Due to the river regulation, the landscape of the entire Glonn Valley experienced a revolutionary change. The many bends in the river, bends and pools disappeared. Today the course of the Glonn runs straight through the valley in a deep bed. The straightening represented a gigantic intervention in the natural balance and the landscape.

To carry out the project, five public cooperatives were set up and the Glonn was divided into five sections. The first construction phase was Allershausen-Petershausen in the area of ​​responsibility of the Freising district office. In this section, 370 landowners were involved with a total of 2,200 daily works.

The bed width at Petershausen was set at 15 m and the depth at an average of 3 m. The second construction phase, Petershausen-Indersdorf, was 12 km long, comprised 1630 daily works of land and 350 landowners. A flood channel near Weichs and an underwater channel near Glonn was built and the mills in Weichs and Asbach were lowered. The third section between Indersdorf and Erdweg was 10 km long and comprised 1,450 days of work and 340 landowners. The stream bed was 2 to 2.5 m deep here and 10 to 12 m wide at the bottom. The lateral drainage ditches were 1.2 to 1.5 m deep and 0.5 to 1.5 m wide. Section four comprised the area Unterweikertshofen-Taxa and section Five Taxa-Egenburg.

The regulated river stretch is 45 km, the additional engine ducts are 9 km long, the entire river stretch was 54 km before the regulation. In addition, 70 km of drainage canals were built. The earth movements required for this amounted to over 2 million m³. The numerous wooden bridges and footbridges leading over the Glonn have been replaced by massive stone bridges. A total of 52 bridges and 14 engines were built. Today the old rights still exist between the mill owners and the district of Upper Bavaria. For the owner, they include the rights to use water power, but also the maintenance obligation for the banks of the Mühlbach and a section of the Glonn.

Consequences of regulation

The strong change in the course of the river and the increase in its gradient significantly reduced the self-cleaning power of the water. This biological function would be extremely necessary today, because a lot of polluted water, u. a. through the sewage works, is discharged into the river. Due to the numerous river weirs, the Glonn is fragmented and no longer even remotely a natural flowing water. Today the water of the Glonn is mainly used to generate electricity. The strong intervention in the Glonn ecosystem is far too high in relation to the low power generation.

With the regulation, the bushes lining the river, the black alders and the willows have largely disappeared . As a result of the dead straight bank embankments, habitats for the fish fry were lost and the conditions for the small organisms that are important as a food source for the fish deteriorated considerably. Not to be underestimated is the fact that the work that took several years and the backfilling of numerous river loops destroyed a considerable part of the fry. All of this led to a sudden break in the sensitive ecosystem from which the river no longer recovered.

Today's protection zones

The landscape protection areas are often very narrow and most parts of the Glonn are used for agriculture up to the banks. In Mühlbach there is a backwater that is not watered by the Glonn itself but by Möslbach. Larger landscape protection areas or nature reserves are located near Weichs and Petershausen.

Fish population and its use

In earlier years the Glonn was one of the most fish-rich waters in Bavaria. Their high fish population was partly due to the relatively mild water temperatures - in contrast to the much colder rivers that arise in the Alps. The temperature in the spring area is 8 to 10 ° C during the summer half-year, which means that the small organisms as a food source for the fish can develop much better and faster. The natural population of the Glonn consisted mainly of rods , whitefish , barbel , bream , tench , aiteln and pike , less of carp .

The conditions for the fish in the Glonn have changed a lot, so that today without artificial stocking by the fishing clubs you would hardly find any fish in the Glonn. Only a few species can reproduce naturally in the Glonn. Since the food supply, the small organisms in the Glonn, is very low for predatory fish due to the pollution, the chances of survival deteriorate. The negative effects on a river were already known at the beginning of our century, as can be inferred from a report from 1903 on the possible damage to fisheries through the correction: "Like any artificial intervention in the natural course of a river, certain changes in the living conditions Due to the fish world, the fishing in the Glonn will undoubtedly suffer considerable damage as a result of the planned correction. On the one hand, it is due to the shortening of the course of the river due to the filling of the river loops that have been corrected . In all regulated rivers the fish population has declined noticeably since the correction was carried out and can only be saved from complete disappearance by taking appropriate measures. " From the point of view of that time, however, the cultural importance of river correction outweighed fishing. The value of the Glonn as fishing water has been significantly reduced. By creating an artificial, canal-like water channel, by removing the natural bank vegetation and the irregularly shaped bank area, many ecological niches that are missing in the river landscape today have disappeared.

Until before the First World War, fishing in the Glonn was only practiced professionally. The main fishing gear was net and trap. Professional fishermen fished the Glonn with flat boats, the so-called barges, and tow nets, especially during Holy Week. The rich catch was sold locally, but above all at the fish market in Dachau and at the Viktualienmarkt in Munich. The earlier tavern in Petershausen with the associated fish water developed into a well-known fish restaurant at the beginning of the century, where fish lovers from near and far stopped for refreshments.

Fed by the water of the Glonn or its tributaries, there are numerous ponds stocked with fish in the Glonntal.

Around 25 different types of fish currently live in the Glonn, the most common of which are food fish such as carp , tench , eel , barbel , pike and pikeperch .

Flora and fauna

The typical tree on the Glonn is the willow. In addition, dead trees, so-called dead wood , mark the river as a territory for re-introduced beavers .

Even black and white poplar are part of the floodplain. This area is called softwood floodplain because of the light, soft wood. The further one moves away from the actual river bed, the finer-grained and loamy the floodplain becomes and the less frequently it is flooded. A completely different kind of forest can develop here. Ash , but especially elm and English oak, characterize the image of the hardwood floodplain that accompanies the river . In the floodplains, the force of the flood breaks without causing any significant damage. One of the functions of the vegetation is to hold the soil with the dense roots. This largely prevents runoff, so that the suspended matter content of the water remains low and the water relatively clear, which could perhaps explain the name of the river in ancient times. In some places of the Glonn you can still see the emerald green color of the water.

Typical bird species are: great reed warbler , reed warbler , marsh tit , sand martin , dipper and chiffchaff .

Tributaries and tributaries

  • Kollbach
  • Röhrersbach (left)
  • Tegernbach (moat) (left)
  • Rettenbach (left)
  • Schweinbach (right)
  • Wood trench (right)
  • Hartgraben (right)
  • Umbach (left)
  • Miegersbach (left)
  • Rossbach (left)
  • Rohrbach (right)
  • Steinfurter Bach (left)
  • Steindlbach (right)
  • Waldbach (right)
  • Zeitlbach (left)
  • Riensbach (right)
  • Hofer Graben (left)
  • Dorfbach (right)
  • Eichhofner Bach or Albersbach (left)
  • Rothbach (right)
  • Gittersbach (left)
  • Langenpettenbach (left)
  • Erlbach (left)
  • Albertshofer Graben (Pasenbach) (right)
  • Ebersbach (left)
  • Asbach (right)
  • Kollbach (right)
  • Möslbach (right)
  • Marbach (left)
  • Old moat in Hohenkammer (left)
  • Moosgraben (right) .

Municipalities on the Glonn

The historical Glonn

Originally, the Glonn flowed dynamically in numerous turns through the wide valley bordered by gentle hills. The banks were bordered by a dense riparian forest . Alluvial forests were originally the natural protection of the surrounding land. A floodplain is the spatial term for those valley zones that are within the area of ​​influence of floods . In the sections further downstream with lower flow velocities, the flood zone often becomes much wider and shows a typical sequence of vegetation: near the river bed, where the river exposes sandy raw soil, a narrow band of willow bushes emerges. This is followed by a forest of tree willows on the same soil conditions.

The development in this country began in the river valleys. Rivers provided the immigrant people with a good orientation aid and the possibility of moving along the banks or in the river bed. The first settlements arose on the slightly higher terraces that were safe from flooding. A typical example of such an elevated settlement is Mühldorf between Petershausen and Hohenkammer.

A change in the river valleys by human hand happened first through the agricultural use of the alluvial forests as forest pastures and later, after the clearing of the forests, as permanent pastures. Occasional floods did not harm either form of use.

The original river bed of the Glonn was much wider and more extensive than it is today, and the water could find new ways depending on the water level. The subsoil in the shallow river bed consisted of light-colored gravel and sand, which at the same time formed into banks. As is shown exactly on old maps, the Glonn divided into several arms for short stretches and formed many meanders in its entire course .

The changes in the course over many decades can still be seen today on old land maps and aerial photographs. River loops were separated from the main river by heavy floods and the oxbow lakes formed from it. The gravel banks constantly changed their shape and small islands and pools appeared and disappeared in the river.

The water depth was very shallow in many places, so that the river could be crossed without a bridge. Until the regulation there were also so-called fords for driving through the particularly shallow water at these points.

Measures for the renaturation of the habitat

Fish ladder on the Glonn west of Asbach ( Petershausen )

The implementation of the water framework directives specifies the goals for the development of the waters, in this case the Glonn. Measures have been implemented in recent years to improve the condition of the Glonn. The required “good status” of the water has not yet been achieved. The “Glonn Working Group” at the Dachau district office has existed since 2001, which deals with the coordination of measures in the entire catchment area of ​​the Glonn.

A resolution of the Bavarian State Parliament of April 27, 1995 states: "The state government is requested to immediately submit an investigation program for floodplain restoration in Bavaria, which also provides for ways of reducing the flow rates and speeds of floods. The following possible solutions in particular should be examined : Reduction of the flow velocity through renaturation of rivers with widening of the channel and the possibility of natural channel relocation; replanting of alluvial forest areas in still or regularly flooded retention areas of rivers and streams. "

For the Glonntal the district office Dachau is part of a high density of auetypischen habitats such as Billabong , fens sought, wet meadows and riparian forests with vital populations-native plant and animal species that also offer enrichment for recreation and space for nature experience.

Individual evidence

  1. ^ Deutsches Gewässerkundliches Jahrbuch Danube region 2006 Bavarian State Office for the Environment, p. 210, accessed on October 4, 2017, at: bestellen.bayern.de (PDF, German, 24.2 MB).
  2. ↑ a b c d e f Lydia Thiel: Glonntal. In: Die Glonn (3rd edition). Bund Naturschutz Landkreis Dachau, accessed on November 7, 2019 (German).
  3. ↑ a b Water Management Office Munich: Water portrait Glonn. Water Management Office Munich, 2018, accessed on November 7, 2019 (German).
  4. ^ Lydia Thiel: Appearance of the Glonn. In: Die Glonn (3rd edition). Bund Naturschutz Landkreis Dachau, accessed on November 7, 2019 (German).
  5. ↑ Lydia Thiel: Water quality map of the Glonn. In: Die Glonn (3rd edition). Bund Naturschutz Landkreis Dachau, accessed on November 7, 2019 (German).
  6. ↑ Horst Kramer: Troubled prospects. In: https://www.sueddeutsche.de/ . SZ Süddeutsche Zeitung, February 26, 2019, accessed on November 7, 2019 (German).
  7. ↑ a b c d e Lydia Thiel: Economic use of the Glonn. In: Die Glonn (3rd edition). Bund Naturschutz Landkreis Dachau, accessed on November 7, 2019 (German).
  8. ↑ a b c d e Lydia Thiel: Glonnregulierung. In: Die Glonn (3rd edition). Bund Naturschutz Landkreis Dachau, accessed on November 7, 2019 (German).
  9. ^ Lydia Thiel: Design of the river landscape. In: Die Glonn (3rd edition). Bund Naturschutz Landkreis Dachau, accessed on November 7, 2019 (German).
  10. ↑ Marcel Fath, First Mayor: The Glonn. In: https://petershausen.de/ . Petershausen community, accessed on November 7, 2019 (German).