Medium flood

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Medium flood is a term that is used for different things:

  • in the maritime sector (for coastal waters ) to designate a specific, regularly recurring height of the tidal high water on the coasts. Storm surge warnings usually relate to the mean flood.
  • for inland waters to designate a weather-related , irregular and exceptional height of the water level of rivers or lakes

In coastal waters


The mean high water ( MHW ), English Mean High Water (MHW) , also Mittleres Tidehochwasser  (MThw), is a measure of the water level of the sea level on coastlines during the tides . It denotes a long-term mean value of the height of the flood. We measure the water level with a "coastal gauge", a mostly automatic level measuring point .


In Germany, the values ​​are averaged over 20 years. The reference height for height information on land is the normal height zero (NHN) . The water level forecast for the German North Sea coast indicates the expected value of the flood and relates to the mean flood. The height of the tide ( tidal range ) for depth information for tidal waters, however, refers to the nautical chart zero .

On the North Sea coast , the mean flood refers to the official coastline in relation to NHN .

On the Baltic Sea, on the other hand, as in other waters without (large) tides (tidal range less than 30 cm), the coastline is defined by the mean water .

United States

In the USA, the values ​​are averaged over 19 years.

In inland waters

In inland waters, i.e. rivers, lakes and other fresh waters , the mean flood is understood to mean:

  • Mean flood discharge (MHQ), that is the long-term mean value of the level or discharge measurement data
  • a moderate flood

There are several different national systems of flood warning levels .

Individual evidence

  1. BSH: Terms from tidal science ( Memento of the original from April 6, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot /
  2. Tidal date . Retrieved January 16, 2015.