Önz
|
Önz Chappelebach |
||
 Lower course of the Önz before the confluence with the Aare (above) near Stadönz, municipality of Graben. |
||
| Data | ||
| Water code | CH : 524 | |
| location |
Mittelland
|
|
| River system | Rhine | |
| Drain over | Aare → Rhine → North Sea | |
| Headwaters | near Affoltern in the Emmental in the Molasse hill country east of the Lueg 47 ° 4 ′ 23 ″ N , 7 ° 43 ′ 22 ″ E |
|
| Source height | 760 m above sea level M. | |
| muzzle | at Graben in the Aare Coordinates: 47 ° 13 ′ 32 " N , 7 ° 43 ′ 12" E ; CH1903: 621 304 / 230 567 47 ° 13 '32 " N , 7 ° 43' 12" O |
|
| Mouth height | 417 m above sea level M. | |
| Height difference | 343 m | |
| Bottom slope | approx. 14 ‰ | |
| length | approx. 24.8 km | |
| Catchment area | 87.6 km² | |
| Discharge at the estuary A Eo : 87.6 km² |
MQ Mq |
1.64 m³ / s 18.7 l / (s km²) |
The Önz is an approximately 25 km long right tributary of the Aare in the Swiss canton of Bern . It drains a section of the Bernese Mittelland and belongs to the catchment area of the Rhine . The catchment area of the Önz has an area of about 96 km².
geography
course
The headwaters of the Önz are located on the municipality of Affoltern in the Emmental , at around 760 m above sea level. M. in the Molasse hill country east of the Lueg . The source stream is called Chappelenbach and flows first in a northerly direction, later more and more in a westerly direction through an erosion valley. In doing so, it takes in numerous short side streams from both sides, which, with their valleys, give the hilly area of the Buchsi- and Wynigenbergs the characteristic relief with steep, often wooded slopes and protruding ridges (harrows).
At Wynigen , the Chappelenbach reaches the Wynigental. At low tide, around a third of the water is diverted to the Wynigenbach , which is part of the Ösch catchment area . The Chappelenbach draws a sharp curve in the area of the village, now flows to the north-northeast and is called Önz from here . She uses the Wynigental, which was once created by the meltwater runoff on the edge of the Ice Age Rhone glacier . The valley has a 300 to 500 m wide, flat valley floor, flanked by steep slopes. On its west side it is flanked by the rounded, once ice-covered forest heights of Ieschberg , Grossholz , Steinenberg and by the height of Steinhof, on which there are still numerous boulders today, mainly made of rock, as occurs in the Val de Bagnes in the canton of Valais . Between these heights there are three transverse valleys (formerly also meltwater channels), which today no longer show any flowing water. To the east of the Wynigental valley rise the Buchsiberge mountains , which were not or only briefly covered with ice during the last ice age and have a strong relief with steep slopes and many short side valleys.
The valley opens north of Hermiswil , and the Önz flows out into a wide gravel plain , which is framed by the ground and terminal moraine walls of the Ice Age Rhone glacier. At about the height of Herzogenbuchsee , the Önz begins to sink into this gravel plain. By erosion it has over time a 10 to 20 m deep and up to 200 m wide valley, called Önztäli , sunk into the environment. At 415 m above sea level M. the Önz flows into the Aare at Graben .
Catchment area
The 87.6 km² catchment area of the Önz lies in the Swiss plateau and is drained to the North Sea via the Aare and the Rhine .
It consists of 34.2% wooded area , 56.8% agricultural area , 8.5% settlement area and 0.4% water area.
The mean height of the catchment area is 578 m above sea level. M. , the minimum height is 416 m above sea level. M. and the maximum height at 886 m above sea level. M.
Hydrology
On the stretch of the river between Wynigen and the mouth of the river, the mean gradient is just 0.67%. The Önz is characterized by a pluvial discharge regime , with the mean discharge rate at Heimenhausen being 1.2 m³ / s. In contrast, in extreme flood events (especially when snowmelt in combination with heavy rainfall), discharge rates of up to 50 m³ / s can be achieved. The Önz has only two major tributaries, namely the Mutzbach (flows into Riedtwil) and the Altache (with the source brook Staffelbach ; flows into Bollodingen ).
The water quality of the stream is heavily polluted by the intensive agricultural use of the areas in the catchment area. In particular, the exposure to nitrate is well above the quality target, while ammonium and phosphate concentrations have been falling in recent years.
fauna
In the Önz there are populations of brown trout , rainbow trout , grayling , bullheads , sunfish , gudgeons and noses, as well as the brown lamprey, which is threatened with extinction in Switzerland .
Since 2004 the beaver has also returned to the Önz. Coming from the Aare, he hiked up the Önz and settled there. In the meantime his traces can be found as far as Hermiswil .
History and use
Since the Middle Ages , the Önz's hydropower has been used in various places to operate mills, sawmills and other businesses. A first major intervention in the course of the Önz was undertaken from around 1850 with the construction of the railway line from Herzogenbuchsee through the Wynigental to Burgdorf . Various minor corrections were then made, before major improvements were carried out between Hermiswil and Wynigen from 1960 to 1989 .
Today the course of the Önz between Wynigen and Herzogenbuchsee is squeezed into a canal bed and straightened, and even overturned on a short section near Wynigen. The Chappelenbach and the winding lower reaches of the Önztäli, which has been a nature reserve since 1983, are still in a near-natural, partially natural state. The lowest section of the route in the area of the estuary has been renatured, further revitalization measures are in the planning phase.
Web links
- Ecological assessment of the course of the Önz river (pdf) ( Memento from September 30, 2007 in the Internet Archive ) (3.04 MB)
- Önztal
Individual evidence
- ↑ a b c Geoserver of the Swiss Federal Administration ( information )
- ↑ Water network in the WebGis geographic information system of the canton of Bern
- ↑ a b Modeled mean annual discharge. In: Topographical catchment areas of Swiss waters: area outlets. Retrieved November 3, 2015 .