Eddy

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Location of an eddy in a river
Eddy water (top side) on a whitewater facility
Play boat drivers wait in the eddy to surf a roller (above)

The term eddy water is used to describe areas in whitewater in which the current turns upstream or at least slows it down considerably. This “reversal” (or slowing down) of the flow direction of the water is caused by the formation of eddies behind obstacles in flowing water. The obstacles can be visible above the water surface or just hinder the main flow of a river under water; in the latter case the eddy is less pronounced and often more difficult to see. Particularly behind river pillars , the eddy water can develop into a vortex with a corresponding current .

The boundary between the main flow and the eddy is called the intersection line or eddy line. Close to the obstacle caused by the eddy (i.e. upstream) it is often actually a clear line. With increasing distance from the obstacle (i.e. downstream) and generally increasing turbulence of the flowing water, however, the line expands into a zone of turbulent water. The passage through the inverse water line requires due to the force acting on the boat different currents a special driving technique (particularly edges ) to at the boundary between eddies and flow - the so-called Verschneidungs- or return water line a - capsizing to avoid the boat.

Due to the often circular vortex movement of eddies, objects such as driftwood can collect here, which, thanks to the changing water levels, can float freely or hang on the bank and reach into the water. They are often impossible to see or difficult to see when approaching and are therefore a danger for paddlers. In addition, there are more often obstacles (mostly stones) directly under the surface of the water in eddies, which were not carried further by the lower current in the eddy and can capsize the paddlers or damage less resistant boats.

Use for whitewater paddling

Eddy waters are suitable for whitewater paddlers to get out of the main current and thus slow down the journey. This is helpful for a short break, to steer the boat into a good starting position for the next section or to get an overview of the further course of the river. In addition, it is easier and safer to get on and off in eddies on the bank than in a full stream.

It is also possible to drive upstream in eddies. On some sections of the river, the paddlers allowed despite strong currents, a lot to gain altitude ( Engl . To attain ): This will only be paddled in a eddies upriver and then quickly switched to the lower region of a further upriver return water as possible; there, further altitude is gained and then, if necessary, a switch is made to an eddy further upstream.

Eddy waters play a special role in play boating and squirt boating . Since eddies make it easier to travel up the river, eddies allow short, flow-intensive sections of the river to be traveled several times without leaving the boat or stopping at the flow of water. Surf waves in particular are therefore particularly popular if they can be ridden repeatedly thanks to an eddy next to them. In addition, play and squirt boat drivers use the eddy lines for tricks, in particular raising the boat ( candle ).

See also

literature

  • Bill Mason : The Art of Canoeing. The Canadian. German adaptation by Arno Gatz and Elmar Engel. 6th edition. Gatz - Verlag für Sport, Natur und Freizeit, Cologne 1998, ISBN 3-9803812-0-X
  • Gary McGuffin, Joanie McGuffin: The fascination of canoeing. HEEL Verlag, Königswinter 2000, ISBN 3-89365-849-1 .