Storm surge

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Storm surge with dike breach (1661)

A storm surge is a tidal current that is increased by a storm with onshore winds .

Definitions

DIN 4049-3 (2005) defines a storm surge as a "rise in the water on the seashore and in the estuaries in the coastal area caused by strong winds when the water levels exceed a certain value."

The classification of North Sea storm surges for Emden, Bremen and Hamburg by the Federal Maritime and Hydrographic Agency (BSH), which is widely recognized in Germany, describes reaching 1.5 to 2.5 m above mean flood (MHW) as a "storm surge"; from 2.5 to 3.5 m above the MHW as a "severe storm surge", and at over 3.5 m as a "very severe storm surge". The mean flood is a term for the mean flood level derived from a sufficiently long series of observations.

description

Elbe terraces in Otterndorf during storm surge

Storm surges occur more frequently on the German coast in spring and autumn. The German Bight is the view of the Federal Maritime and Hydrographic Agency (BSH) one of the hardest hit by storm surges threatened areas worldwide. Due to the geography of the North Sea coast and the funnel effect of the Elbe estuary , this phenomenon occurs more frequently there than elsewhere.

Storm surges pose a threat to the affected coastal regions from flooding if they break through the man-made dikes . Storm surges give waves a considerable amount of energy. In the Middle Ages , storm surges changed the course of the coast in the North Sea area and created large bays such as the Jade Bay and the Dollard .

History of storm surges on the North Sea coast

Affected area during a very severe storm surge of 4.5 m when a dike breached at Glameyer-Stack , Otterndorf

Storm surges and their effects have been known since Roman times . Reliable information is available - until recently - for the extent of the respective land losses. It is not known which storm surge was the most devastating in terms of deaths. The earlier data on the number of dead are very contradictory; It can be assumed that some figures were overstated with regard to the medieval settlement density on the North Sea.

On around 340 BC The great Cimbrian flood is dated. Around 120 to 115 BC In Jutland many people seem to have perished in a storm surge. However, there are great doubts that this could have been one of the factors behind the migration of the Cimbri and Teutons , as more weighty reasons are necessary for entire peoples to give up their habitat than a storm surge on the coast.

Around 1134 a storm surge occurred in Flanders . As a result, a sea arm ( Zwin ) was created, which extended as far as Bruges and later gave the city access to the sea via the canalized river Reie. During the Julian flood in 1164, around 20,000 people died in the Weser and Elbe regions and in East Frisia .

The most important storm surges of the Middle Ages are the First Marcellus Flood of 1219 and the Second Marcellus Flood or Grote Mandränke of 1362. In both floods, the course of the coast changed drastically: islands were destroyed, divided or created and large tracts of land on the mainland were lost overnight. There were tens of thousands of dead and dozens of villages lost. In the First Marcellus Flood, the Zuidersee , today's IJsselmeer , was created, killing around 36,000 people. In the case of the Groten Mandränke, the - perhaps somewhat exaggerated - estimates go up to 100,000 deaths. It is certain that 30 villages were destroyed in one night, as a result of the storm surge through the destroyed dikes, a total of 44 villages. Many other villages were cut off from the area for many years and became islands, including Asel near Wittmund.

Since the Middle Ages, a flood disaster has occurred in every century on Dutch territory, causing great damage and many victims:

  • In 1347 and 1376, the storm tides tore away large parts of the country and destroyed hundreds of villages and their inhabitants, the Dollart was created and the Jade Bay was enlarged many times over.
  • In the 15th century it was the Elizabeth flood in 1421 ,
  • in the 16th century the All Saints flood in 1570 ,
  • in the 17th century the Burchardi flood of October 11, 1634. With the approaching end of the Little Ice Age , economic conditions became more stable; after the Burchardi flood an important turning point in dyke construction took place, see history of dyke construction .
  • The Christmas flood of 1717 followed in the 18th century ,
  • in the 19th century the February flood of 1825 .
  • The flood disaster of 1953 is considered to be the worst storm surge of the 20th century in the Netherlands and England. The Dutch Meteorological Office only counts this in the category of severe storm surges in the 20th century, while the particularly devastating flood of February 17, 1962 in the Netherlands only expressed itself as a medium storm surge.

The victims of the storm surges of 1953 (especially in the Netherlands ) and the storm surge of 1962 (especially in Germany and Denmark ) prompted extensive coastal protection measures such as the Delta Works . These enormous investments in coastal protection, in particular through the construction of dykes and barrages , have ensured that the recent storm surges caused far less damage than earlier, lower storm surges.

Big storm surges

Record of water levels during storm surges

Memorial stone indicating the height of various floods at St. Margaret's Church in King's Lynn , East England
Heights storm flood data.svg

For the North Sea there have only been regular records of water levels since 1840 ; After the introduction of automatic level recorders, continuous records were made from 1880 onwards. From such sufficiently long observation series, average water levels are calculated and key data are derived which are used for the water level forecast, whereby meteorological data facilitate the forecast.

Water level (WS) is the current height of a natural or artificial water level in relation to a reference level for water level measurement, whereby different height systems and reference points are used depending on the country . For the North Sea, the Amsterdam level ( NAP; Normaal Amsterdams Peil ) is the most important reference point.

Mean water (MW) represents the mean water level over a longer period of time when measuring the water level, which is calculated as the arithmetic mean of equidistant, mostly hourly water levels over this period. This term is generally only used inland, where there is little or no influence from the tidal current. Mean flood (MHW) is the derived mean flood level or the mean flood height (MHWH). Tidal range (TH) is the difference in height of the water level as the tides change . Particularly high tides at full and new moon be Spring floods or colloquially (SPHW) Riptide called; they can develop into a storm surge due to tidal waves and wind ( drift current ).

If the water on the North Sea coast rises more than 1.5 m above the mean high water level (MHW), one speaks of a storm surge, from 2.5 m of a heavy and from 3.5 m of a very severe storm surge. It is created by the interplay of wind and tides , whereby both the wind strength and its duration play a role. If the moon and the sun are on one axis to the earth, the tidal forces add up to a spring tide at a new moon, which leads to particularly high water levels.

Storm surges are not uncommon on the North Sea coast. They have been handed down from 1000  AD , they changed the course of the coast and created large bays . They pose a threat to the relatively flat coastal regions from flooding, as far as they spill over the top of the dykes or even break the dykes. The inhabitants of the coastal areas have learned to deal with the complex of mounds , dikes , sluices , flood fight and windmills to protect (as scooping mills for drainage).

Nowadays storm surges are divided into light, medium and heavy floods according to the height of their water level. As long as there were no exact statistics of the water levels, they were rated according to the damage they caused. On average every two years a storm surge occurs on the Dutch North Sea coast, which is categorized as light and usually proceeds without major damage. Medium storm surges, which statistically only occur every 10 to 100 years, and heavy storm surges, which occur every 100 to 1000 years, are more dangerous, but also less frequent.

Storm surges and water levels

The following table contains the water levels measured during storm surges from 5 m above sea ​​level using the example of the Hamburg-St. Pauli and, in comparison, the water levels in Cuxhaven.

(N = new moon; V = full moon; Diff. = Difference)
date St. Pauli Cuxhaven Diff. Remarks
Jan. 3, 1976 N 6.45 5.10 1.35 Highest level measured so far
Dec. 6, 2013 N 6.09 4.64 1.45 second of three storm surges caused by hurricane Xavier
Jan. 28, 1994 V. 6.02 4.50 1.52
Jan. 10, 1995 V. 6.02 4.48 1.54
December 3, 1999 V. 5.95 4.50 1.45
Nov. 24, 1981 V. 5.81 4.75 1.06
Jan. 23, 1993 N 5.76 4.34 1.42
Feb. 28, 1990 N 5.75 4.44 1.31
Feb. 5, 1999 V. 5.74 4.50 1.45
Feb. 17, 1962 V 5.70 4.95 0.76 see storm surge 1962
Nov 9, 2007 5.40 4.41 0.99
Jan. 28, 2002 V 5.26 3.84 1.42
Feb. 4, 1825 B.C. 5.24 4.66 0.58
Jan. 30, 2000 N 5.16 3.94 1.22

Global warming

Population density and height above sea level in Hamburg and Bremen

In the course of global warming due to an increased greenhouse effect , scientists expect an increase in the risk of storm surges due to three effects: increased probability of storms, increased storm intensities and a general rise in sea level .

Storm surge risk analysis

The storm surge risk analysis was published in 2014 as part of the risk analyzes in civil protection carried out by the German Federal Office for Civil Protection and Disaster Assistance (BBK) .

The analyzed storm surge scenario assumes a two-day winter storm, which leads to a very severe storm surge and hits the entire German North Sea coast, the Netherlands and Denmark. The highest water levels occur in Hamburg, Bremerhaven and Husum. The water levels do not exceed the dyke heights, but waves overflow, which causes dike breaks and flooding of the hinterland, sometimes with considerable damage. The storm caused long-lasting power outages nationwide.

  • The winter storm hits 30 million people and causes 110 deaths.
  • The flooding affects 150,000 residents and causes> 150 deaths.
  • The long-lasting power outages affect more than 6 million people and cause around 1,000 deaths.

The frequency of occurrence is determined to be 1 × in> 10,000 years.

Others

Storm surges also became the subject of literary works such as in the novella Der Schimmelreiter by Theodor Storm , who also describes the development of dyke construction on the North Sea in the 19th century in a very interesting way . The storm surge is often referred to as Blanker Hans in German literature as well as in song lyrics .

See also

Storm surge column in Bremerhaven ( Gerhard Olbrich )

literature

Web links

Wiktionary: Storm surge  - explanations of meanings, word origins, synonyms, translations
Commons : Sea Storms  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b storm surge . ( Memento from September 23, 2015 in the Internet Archive ; PDF; 13.6 MB) bau.uni-siegen.de; accessed on July 4, 2019.
  2. ↑ WJ Beckers: Teutons and Cimbri in recent research. (PDF) rhm.uni-koeln.de; accessed on July 4, 2019 (PDF; 5.1 MB).
  3. ↑ Hans Georg Wunderlich: Introduction to Geology, Volume I, Exogenous Dynamics. Bibliographical Institute Mannheim / Vienna / Zurich, BI-Wissenschaftsverlag, Mannheim, 1968, p. 118.
  4. ↑ Chronicle of the storm surges. ( Memento from May 6, 2010 in the Internet Archive ) die-ganze-nordsee.de; accessed on July 4, 2019.
  5. ↑ Terms from tidal science. ( Memento of April 6, 2009 in the Internet Archive ) In: Federal Maritime and Hydrographic Agency website . Retrieved July 4, 2019.
  6. ↑ How are storm surges defined? ( Memento from December 26, 2017 in the Internet Archive ) In: Federal Maritime and Hydrographic Agency website. Retrieved July 4, 2019.
  7. ↑ Beukema: De orkaan van 1953. p. 14.
  8. ↑ Marcus Petersen, Hans Rohde: Storm surge. The great floods on the coasts of Schleswig-Holstein and in the Elbe. 3. Edition. Neumünster 1991, ISBN 3-529-06163-8 , p. 9 ff.
  9. ↑ dossier Stormvloed. ( Memento of January 9, 2008 in the Internet Archive ) KNMI website (Dutch) accessed on July 4, 2019.
  10. ↑ K. Stockmann: The North Sea storm floods from December 5 and 6, 2013 . ( Memento of December 10, 2017 in the Internet Archive ; PDF; 3.2 MB) Federal Maritime and Hydrographic Agency website; accessed on July 4, 2019.
  11. ^ Report on risk analysis in civil protection 2014 (PDF) In: 18th German Bundestag, printed matter 18/3682, 23 December 2014 - Storm surge risk analysis .