Intertwined river
A braided river (English Braided river ; German also verwilderter flow , verzopfter flow , Zopfstrom ) is a special form of a branched flow barrel, in which the flow at low water splits into a network of small channels through small islands ( braid bars British in English aits or eyots ) are separated.
The channels and islands are often highly changeable, as their position changes again and again due to the rapidly advancing sediment deposition , and the course of the river often changes drastically as a result of individual floods. Intertwined rivers are typically found at the exit of high mountains (wide, flat valleys, low slopes, periodically fluctuating amounts of water) as well as in arid (here one speaks of torrents ) and arctic areas, they are often found in alluvial cones and on rump areas.
Demarcation
The branches found in the lowlands on the lower reaches and deltas of the rivers are often referred to as intertwined rivers, but count among the anastomosing rivers because they arise differently.
Anastomosing rivers build up due to the high sediment load and their low gradient and are also known as ramified dam bank rivers . The so-called alluvial fan does not grow evenly in height. Rather, the river sediments in the immediate vicinity and forms the typical bank walls. The latter cause tributaries to flow in parallel for longer stretches before they finally flow either into the river or into the sea parallel to it.
If oxbow lakes and pools lie somewhat lower in the rest of the wide valley and a bank wall breaks (e.g. after floods ), a tributary arises in these deeper areas until these are also filled with sediment. Depending on the height of the embankments, dam bank lakes can also arise, which are often boggy.
education
The formation of this flow form is promoted by
- heavy sediment load
- strong and regular changes in the flow rate
- easily erasable material from the banks.
The water flow is seasonal, for example on the snowmelt, which leads to very different water flow and strong floods.
Intertwined river systems arise, among other things, where a drastic reduction in the gradient of a river leads to sediments being deposited so quickly that the river cannot carry them away. Here it depends on the gradient whether a meandering or an intertwined river course is formed. A meander is created with a slight gradient, an intertwined river course with a larger gradient.
The individual channels of the river system meander due to their different water velocities: On the impact slope , on the outside of a curve, the river removes material due to the higher flow velocity, on the inside of the curve with its low flow velocity, material is deposited again.
The entire river bed can lie in an area delimited by relatively stable banks or it can occupy the entire valley floor. So who Rakaia River in the region Canterbury in New Zealand , for example, 100 m deep channel in the surrounding plain cut one, which is rather unusual for this valley shape.
The sediments, mostly sand and gravel, are deposited mainly at low tide. The river bed sediments are stratified horizontally and are not sorted according to grain size.
The constant change in the course of the river and the uneven terrain make the bridge construction difficult.
Occurrence
Extensive systems of intertwined rivers existed primarily in regions of the world that host young, heavily eroded mountains. Examples of intertwined rivers can be found widespread in Alaska , Canada, or the South Island of New Zealand. In the Himalayas , the Brahmaputra is an example of an intertwined river, and the course of the Yellow River is also part of this river class.
A well-known intertwined river in the United States is the Platte River in Nebraska . The sedimentation of the material from the arid Great Plains is increased here by the presence of the nearby sand hills in the north.
On the vast sandy areas in Iceland there are often intertwined rivers that have emerged from glacial rivers. So over the sander Skeiðarársandur in the southeast of the island with the rivers Skeiðará , Gígjukvísl or Núpsvötn flow some larger intertwined rivers.
In Central Europe, for example, sections of the Lech in Tyrol and the Tagliamento in Friuli should be mentioned.
Many other rivers in Central Europe also show evidence of the existence of intertwined river systems during the Ice Age, which today have been replaced by a meandering system due to the change in climatic conditions, such as the Weser.
See also
Individual evidence
- ↑ Geography lexicon: River branching ( Memento of the original from January 10, 2014 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. On: geodz.com
- ↑ Geography Lexicon: anastomosing river ( Memento of the original from November 25, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. On: geodz.com
- ↑ a b Manuel Pfaff: The Brahmaputra and its tributaries. (No longer available online.) Geographical Institute of Johannes Gutenberg University, Mainz, formerly the original ; Retrieved February 28, 2009 . ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ Hans Füchtbauer: Sediments and sedimentary rocks . 4th edition. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart 1988, ISBN 3-510-65138-3 , pp. 93 .
- ↑ Susanne Lipps, Gerfried Caspers: Late Glacial and Holocene on the Stolzenauer terrace in the Mittelwesertal. ( Memento of the original from March 5, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Ice Age and Present, Volume 40, ISSN 0424-7116 , doi : 10.3285 / eg.40.1.09 , pp. 111-119, 1990
literature
- Patricio Silva González: Braided rivers. Chapter 3.3.2.2, p. 51ff (pdf, 728 kB). In: The South Altiplano Basin (Bolivia) in the Tertiary: Sedimentary development and tectonic implications. Dissertation Free University of Berlin 2004
