ebb
The sinking of the sea level as a result of the tides (tides) is called ebb or running water . The opposite is called flood (rising). The term ebb also describes the period between high and low water .
The colloquial term "ebb" for every low water or generally a low water level is therefore incorrect. However, this use of the word is widespread and is also used slang to denote a low level in general, e.g. B. The tide is ebb in the account , The treasury is ebb .
Effects
At low tide in are coastal and - shore parts of the sea - or river bottom exposed. In the Wadden Sea in the North Sea , the so-called mud flats fall dry. At this time, mudflat walks are possible. The tidal flats represent a special habitat for flora and fauna .
The duration of the drying out determines the zoning of the habitat and the corresponding animal and plant species.
Depending on the geographic location and the constellation of the moon, sun and earth, the difference between high and low tide is different. The highest tidal range of 14 to 21 meters occurs in the Bay of Fundy in Canada. In the North Sea it is three to four meters, in the Mediterranean and the Baltic Sea less than half a meter.
Anthropogenic changes can change the mean water levels at low tide (as well as at high tide), as can be seen from the example of the Elbe. Here the mean low water level has decreased to this day with the start of deepening work on the river bed in the Elbe estuary.
Ebb stream
The ebb current is the flow of water that occurs at ebb tide. The ebb current can develop considerable speeds depending on the tidal range and sea relief. In the Elbe in front of Cuxhaven , current speeds of over 6 km / h can occur during spring tides . Such a current becomes particularly strong when the water collects from a larger area in a tidal channel, i.e. a river bed-like depression in the sea floor, and flows away from the shore with great force. If a swimmer is caught in an ebb current, it can be carried far into the sea. If he cannot find help there or swim back on his own, he can drown . This also applies to the use of air mattresses, paddle boats, row boats and pedal boats, and ships with little motorization. That is why there is a lifeguard station or corresponding warning signals (flags) at bathing beaches that are at risk .
In the tidal river
Also tidal rivers like the Elbe , the brackish water or fresh water lead to have tides. The ebb or ebb time is also the period between high and low tide. The end of the ebb, i.e. the lower apex of the tidal wave, is known as low tide. The water level and tidal current do not always coincide, which is why, in addition to high and low water, the term capsizing of the high and low tide is also used. For example, in river mouths the ebb current can continue to run on the surface while the water level is already rising again, so that the ebb current only capsizes after low water.
Web links
- Calculation of tides at the Federal Maritime and Hydrographic Agency (BSH)
- Calculation of the currents at the BSH
Individual evidence
- ↑ Fickert, M .; Strotmann, T .: Hydrodynamic development of the tidal Elbe . Hamburg, S. 2007 .