The rise of the water level as a result of the tides (tide) is called high tide. This period ranges from a low water to the following high water . On the coast, the term accumulating water is also used to differentiate between inland floods or inundations. The subsequent drop in sea level is called the ebb ( running water ). The flood is not to be confused with the high water. High tide indicates a direction of movement, while high tide marks the highest level of water.
The height of the tide above sea level is not the same everywhere. In the Baltic Sea, which is relatively cut off from the oceans , it is 10 cm, on the open North Sea it is mostly 100 cm. The tidal range of the Atlantic is only 50 cm in the area of the mid-Atlantic ridge . It is much higher on coasts , bays and estuaries , where the water mountain has to pass narrow points. In the estuaries of rivers, for example the Elbe and Weser , up to 4 m is reached, in storm surges up to 10 m. The tidal range can still be felt on rivers inland, provided there are no barriers and the difference in altitude is small ( tidal flow ), e.g. B. Amazon , Thames , Elbe , Weser, Wümme , Ems . The tidal range on the English Channel is up to 12 m, on the Bay of Fundy from 15 to 21 m. Anthropogenic changes can change the mean water levels at high tide (as well as at low tide), as can be seen from the example of the Elbe. Here the mean high water level has risen steadily with the start of the expansion work in the Elbe estuary.
In storm surges , the force of the wind increases the water level above normal. This allows water levels to be reached that are 3 to 5 meters above normal mean high tide (MTHW). In the past, storm surges have claimed considerable casualties , particularly on the coasts of the North Sea . B. 1962 in Hamburg .
- Fickert, M .; Strotmann, T .: Hydrodynamic development of the tidal Elbe . Hamburg 2007.