Bar (river morphology)

As gravel bars (also called Heger or Haeger ) refers to elongated, at low water falling dry surfaces in larger streams and rivers. The river carried from the stones ( boulders, gravel) and larger quantities of sand are deposited on those points of the riverbed, which have low depth and where there is little or no flow.

Although gravel bars form at all running waters that have sufficient flow velocity necessary to move coarse material -rich sediment, and the fluctuating over the course of the year water levels have, they are especially typical of rivers with a branched channel shape, which is also called Flussverwilderung. These forms, when the slope of the water and the sediment transport are high. In low gradient, it turns into a meandering channel forms. Branched flume exist at high water level of a network of diverging and soon again be united ( " anastomosing " ) partial waterways that can be freely between characteristically rhombic shaped " islands". With decreasing water level the shallower part of these waters dry up and the "islands" are larger, until only a body of water is left in extreme cases. Typical of branched flume is a broad, mostly vegetation -free flood bed (often with higher islands with tree plantings ) with a low-water bed, which can be shifted after each major flood in it. Due to the high dynamics arise particularly large gravel banks.

The gravel bars are colloquially, such as gravel islands referred to as islands. This is, however, just as in the case of sandbanks, scientifically incorrect.

Since the water level of almost all alpine rivers is constantly changing in the decimeter, gravel banks freshly formed soon be flooded again, partially eroded and transported to other parts of the river bed.

For geologists gravel banks have a special meaning: for the former, they represent a diversity, a virtually unsurpassable rock collection, the rapid notes brings to the petrography of the entire catchment area and allows to estimate also the amount of average erosion.

For the bird world, and especially dieWasservögel the gravel / sand / gravel banks, however, are treasure troves of another kind: there are in the pores plenty of small creatures, and still loose sediment provides a search against a large resistance. On the other hand, the accumulation of gravel banks excrement of birds important information on the nutritional and train behavior of the two-legged visitors for Ornithology.

Vegetation arms gravel banks are also important breeding grounds for birds, such as the Ringed Plover (Charadrius dubius ). Gravel banks, particularly those of the Alpine rivers and the Upper Rhine, are about hinau habitat for specialized invertebrate species. For example, the locusts were given. The in Germany endangered species gravel - grasshopper ( Chorthippus pullus ), Türk thorn Grasshopper ( Tetrix Turkish ) and Green beach cricket ( Aiolopus thalassinus ) live exclusively or predominantly on gravel banks.

In botany, the gravel banks of the Alpine rivers are known as a forward outpost of the presence of typical alpine plants. It is believed that the seeds of these species are brought in on the flowing water. The vegetation-free gravel bars correspond in many respects the alpine habitats, from which the species. Also, here is missing the competition from other plants. Occurrence of such Alpenschwemmlinge are known in the river Isar to Munich and the Lech to the north of Augsburg.

While occurring on gravel benches grain sizes range up to a maximum of about 10 cm sized pebbles, the heavier sediment is deposited elsewhere because must not exceed under - and for stones over about 1 kg of the flow very specific limits. However, at high water, all these formations relocate large scale