An oxbow lake is a former arm of the river that no longer has any connection to the main stream and has therefore become a still water . With its preliminary stage, the oxbow lake , it is summarized under the term old water body .
An oxbow lake (also known as a dead arm ) is the part of a river that is cut off at one end from the main stream by natural (sand or gravel bank) or artificial ( weir or dam ) action. Old arms are flatter and closer to nature than the main arm. Since there is no more or only little flow through them, they tend to become swampy or even silt up , but serve as an emergency drain during floods. They form an important habitat for birds and insects and are mostly designated as nature reserves or landscape protection areas. Oxbows often arise from side branches. If there is no longer any connection to the main stream on either side, the backwater becomes the backwater.
- Connection to the main stream only at one end
- There is little flow (e.g. only via a bottom outlet ) or there is no longer any flow, except during floods
Example: Saumain in Schweinfurt
An oxbow lake is a part of a river with standing water that is completely separated by natural or artificial effects (see: oxbow river), i.e. a still water . They often arise naturally in rivers with a slight longitudinal gradient when they break through the meander , while rivers with naturally branched water beds (furcations) rarely form backwaters. Even more rarely, a river can completely shift its course within the floodplain (“river jumping”) during a disaster flood, for example the Elbe near Schönebeck in the Middle Ages . Backwaters are naturally part of the floodplain landscape . Since they are no longer traversed, backwaters, like all standing waters, are subject to natural silting and eutrophication , due to the entry of mineral sediments during floods and the accumulation of organic sludge or peat through plant production. In the lowlands they naturally have an age of up to a few hundred years. If their regeneration is prevented by restricting the natural flow dynamics, they will gradually disappear by themselves.
Like oxbow lakes, oxbow lakes form an important habitat for birds and insects. Some have now been designated as nature or landscape protection areas, for example the Kühkopf-Knoblochsaue nature reserve on the Middle Rhine.
Backwaters arise from side arms, backwaters, remnants of flood arms or from old stretches of a shipping canal that no longer have a connection to the canal. Where they are not sealed off, they form important emergency drains and natural retention areas (catch basins) during floods .
- No more connection to the main stream
- No longer flowed through, except possibly by smaller backwaters such as streams
Example: Sennfelder Seenkranz near Schweinfurt
In navigable waters, especially in shipping canals, an old voyage can arise if a new voyage is created in addition to the original route and both routes continue to be used for shipping.
Old stretches of a shipping canal are still connected to the main course of the canal on both sides or on one side, but are usually no longer of any significance for shipping.
Backwaters of rivers are ecologically classified in limnology according to a system developed by the French limnologist Claude Amoros . The typification is based on the connection to the river, in connection with succession and silting processes . The different types can, as a time series, be understood as different stages of a dynamic development of a certain section of the run. The system is used to describe bodies of water as habitats and their flora and fauna, especially the fish fauna.
- Eupotamon : The flowing water through which it flows. This may include the main arm and various secondary channels of an anastomosing river through which flow occurs .
- Parapotamon : old arm tied on one side. There is no noticeable current here at low tide, but the water is open to the main course, so that both water and organisms such as fish are exchanged.
- Plesiopotamon : At least completely separated backwater at low tide, for example a meander loop tied off on both sides. Due to the separation in the water chemistry and the temperature, the conditions can be completely different from the flow through the river or an oxbow river connected to it. Often, however, there are still small connections with little flow, which have hardly any effect on the physical or chemical conditions, but allow fauna to be exchanged.
- Paläopotamon : "ancient water". Heavily silted up backwater, often characterized by a thick layer of sediment made of mud, which is only in contact with the river during extreme floods. They gradually turn into troughs and troughs that no longer carry water.
- DIN 4054 hydraulic engineering; Terms; September 1977
- Volker Lüderitz, Uta Langheinrich, Christian Kunz: Old river water: Ecology and remediation. Vieweg + Teubner Verlag, Wiesbaden (Springer Verlag) 2009. ISBN 978-3-8348-9976-7
- C. Amoros, C., A. L. Roux, J. L. Reygrobellet (1987): A method for applied ecological studies of fluvial hydrosystems. Regulated Rivers: Research and Management 1: 17-36.
- Ulrich Schwevers and Beate Adam: Assessment of floodplains using the fish fauna - feasibility study. BfN-Skripten 268, 2010 BfN Federal Agency for Nature Conservation, Bonn.
- Tanja Pottgiesser: Typification of potamal backwaters in Saxony-Anhalt. Expert opinion on behalf of the LHW State Office for Flood Protection and Water Management Saxony-Anhalt, State Hydrological Service, Ecology Department, 2012. PDF
- Ecological parameter: hydrological preference www.freshwaterecology.info Database, accessed August 31, 2018.