The tidal range ( ndd. Tide , tied = time) indicates the extent of tide-dependent increases ( high tide ) and decreases ( ebb ) of the water level. Tidal range is the difference between the lower water level ( low water , NW) and the peak level ( high water , HW). From the rise of the tide (TS) and the fall of the tide (TF) the tidal range results as an arithmetic mean . For the indication of the water levels of HW and NW, in addition to the respective official reference level , the sea chart zero (SKN) has been used as a reference level in recent years .
Since the tides depend on the position of the moon and the sun in relation to the earth, the sequence of high and low water, the tidal curve, changes in a period that depends on the phases of the moon . The time interval between two successive high tides is about 12 h 25 min, so that the times of high tide and low tide shift from day to day. The tidal range also changes. The maximum spring tide is called the minimum nipp tide .
In addition to the tides, the wind direction and wind strength influence the real mean water level and thus also the high water height (HWH) and low water height (NWH). It is particularly threatening when a storm surge coincides with a spring tide.
The geomorphology of the seas and their coasts has a considerable influence on the tides . The tidal range in the western Baltic Sea is only around 30 cm, on the German North Sea coast around 2 to 3 meters. In the estuaries of the tidal rivers , e.g. B. Elbe and Weser , the tidal range is up to 4 meters due to the funnel effect. Tidal waves like Ebbetal migrate upstream until they run out at the tidal limit. Since the tide of the Lower Elbe takes about 6 hours to reach the tidal limit, z. B. In Geesthacht high tide when in Cuxhaven is low tide, and vice versa. The lithosphere is also subject to a tidal range that is in the range of a few decimeters.
The tidal range is higher than in the German coastal waters at Saint-Malo in France or in the Severn estuary and in the Bristol Channel between Wales and England , where it can reach 12 meters (in Sudbrook ). There are also particularly high tidal fluctuations on the east coast of North America: Probably the largest tidal range on earth is found on the Bay of Fundy in Canada, between the Canadian provinces of New Brunswick and Nova Scotia . There the tide of the Atlantic Ocean presses into a bay and causes a tidal range of up to 15 meters; the southwest of Ungava Bay in the Canadian Arctic reaches a similarly high value . The maximum value for the Pacific Ocean is reached in the Peninsula Bay of the Sea of Okhotsk at almost 13 meters.
Expansion measures in tidal rivers can lead to an increase in the tidal range. Dike construction and the construction of barriers increase the funnel effect. Dredging and river straightening lead to an acceleration of the currents. The local peak of the tidal range shifts upstream. Since the flow acceleration affects not only the pendulum movement of the tidal current but also the overall movement of the river water towards the sea, the lowering of the low water is usually more pronounced than the increasing of the high water. The expansion of the Lower Elbe in the second half of the 20th century led to an increase in the mean tidal range at the St. Pauli gauge from 1.80 meters before 1840 to over 3.60 meters (1995).
- Tides , section tidal range , www.physik.wissenstexte.de (online)
- Hartmut Kausch: Can you deepen the fairway without limits? In: José L. Lozán, Hartmut Kausch (Ed.): Warning signals from rivers and estuaries. Scientific facts. Parey, Berlin 1996, ISBN 3-8263-3085-4 , pp. 162-168. In: Kathleen Giersch: Commented literature research on the subject of reed beds. University of Bremen 2002, p. 45.