Storm surges on the Wadden Sea Coast

Klaus Melbye, Vadehavscentret & Anne-Marie Overgaard, Museum Sønderjylland

tide & lAndScApe

translation: nanna Mercer, Sirius translationpage 1 of 4

Many of the Wadden Sea coastal storm surge pillars mark the storm surge in 1636

StORM SURGeS On tHe WAdden SeA cOASt WHen tHe WAteR RUSHeS FORWARd

The inhabitants on the Wadden Sea coast have always lived with the threat of storm surges that flooded their fields, caused devastating damage to their properties and, at the worst, loss of life. Still, storm surges were not only the ultimate fight in the past between nature and culture, but also future dramatic landscape challenges for the Wadden Sea region.

A storm surge occurs when a storm causes the sea level on the ocean to rise faster than normal, thus causing devastating damage through flooding. The rise in the sea level is caused by a combination of water piling up, tidal flow and low atmospheric pres-sure. The water piles up when the ocean is pushed towards land by a strong onshore wind that causes the water to rise along the coast. The worst imagina-ble situation is therefore when a heavy storm hits the coast at the high tide after a long period with heavy onshore winds.

Under normal circumstances, the atmospheric pres-sure near the earth’s surface is 1013 hPa on ave-rage, but during a storm it drops to 970-980 hPa. Since a drop of 1hPa in the atmospheric pressure will cause the sea level to rise by 1cm, such a drop in atmospheric pressure will increase the sea level with up to 0.4 cm.

How or how long storm surges hit is therefore very diverse For example, the storm surge in 1981 de-veloped over 4 or 5 high tides, while the tornado on Dec. 3rd in 1999 only lasted between 2 and 3 hours

while also hitting at the low tide. In 1999, the incre-ased sea level was caused by the effects of the wa-ter piling up and the drop in atmospheric pressure, and the piling up contributed with a 5.5 m rise in the sea level.

the Great drowningsTwo storm surges stand out in the history of the Wadden Sea. The Great Drownings in 1362 and 1634 caused huge changes in the Wadden Sea landscape, and they both caused devastating da-mage and a huge loss of life.

The day in 1634, the second Great Drowning, is well documented and has left an indelible imprint not only on the landscape, but also in the consciousness of the people living on the coasts. The fishing village Sønderside, situated by the current Havnegrøft on Skallingen, had to be given up after the storm surge, and in Ribe Cathedral the sea level was marked on the stone pillar by the pulpit. Many of the storm surge pillars on the Wadden Sea coast also note the water level in 1636.

See SignS after Storm SurgeS in ...

AUTUMN WINTERSUMMERSPRING

Klaus Melbye, Vadehavscentret & Anne-Marie Overgaard, Museum Sønderjylland

tide & lAndScApe

translation: nanna Mercer, Sirius translationpage 2 of 4

From only low summer dikes made to protect the crops, man started building real ocean dikes, who-se primary function was to protect the people living along the Wadden Sea. The oldest dikes are found in Tøndermarsken, in Germany and in Holland whe-re settling in the marshland on man-made terps was very widespread. However, the dikes along the nar-rower marshland to the north are only between 100 and 150 years old. Here, people settled on the edge of the Geest.

the ocean dikesThe ocean-dikes with their sloping incline facing the ocean are more resistant to wave attacks since the waves slowly burn up their energy going up the slo-ping incline, rather than hitting the dike full on. At the same time, with an increased sea level, a dike is also exposed to amplified bottom pressure since this is where the water pressure is greatest because of the column of water overhead. Therefore, it makes sense that a dike is the widest and the strongest on the bottom for, among others, to delay the water per-colating at the base of the dike causing solifluction and collapse.

Today, there are dikes on most of the almost 500km long stretch from Ho Bugt and Esbjerg in the north to Den Helder in Holland to the south. Only a few places are without dikes: Ho Bugt and Varde Å, and where the moraines extend into the Wadden Sea near Hjerpsted and Emmerlev Klev.

the ”new” storm surgesThe storm surges in 1976, 1981 and 1999 have each raised questions about the strength of the dikes.

The storms on January 3 and 21, 1976 caused great damage to the dikes with a ca. 4.8 meter increase in the sea levels. On January 3rd, around 16:00, 20,000 people from the marshland regions near Ribe and Tønder were evacuated to more elevated ground. As something new, RadioSyd reported on the situation and since then the radio has been a part of Storm Surge Preparedness. These storms were the reason why Det Fremskudte Dige by Højer was built, just as the Ribe Dike was made higher.

The storm in 1981 developed over 5 high tides from November 23th - 25th with a 5.11m increase in the sea level by Ribe Kammersluse. With winds up to 30 m/s, the storm caused great damage along the coast, but it was worst on Mandø where the dike was

A storm surge is a situation where a storm causes the sea level to rise much higher than normal

The storm surge in 1825 did terrible damage to the then Danish island Føhr and the terps on Hallig Hooge. This natural disaster resonated in the minds of the Da-nish people and caught the attention of King Frederik IV. However, during his trip to the Halligen, the King was caught in a storm and had to stay overnight. To-day, the living room ”Königspesel” is one of the great local attractions.

the king waS SurpriSed ...

Klaus Melbye, Vadehavscentret & Anne-Marie Overgaard, Museum Sønderjylland

tide & lAndScApe

translation: nanna Mercer, Sirius translationpage 3 of 4

damaged in more than 100 places. The island was partially flooded when the water broke through the dike in seven places and Store Rende was flooded with 4.50 meters of water. All told, 200 sheep and 18 head of cattle downed. At the smallholdings along-side the town dike, the water came up to the middle of the windows. Most of the houses in Mandø town are situated in the dunes and so were not flooded.

On December 3rd, 1999, a hurricane hit the Wad-den Sea coast for the first time, but as luck would have it, at the low tide. The hurricane made landfall at around 19:00 causing an increase in the sea level of ca. 5 meters with record-high gusts of wind of up to 53m/s measured on Rømø and in Vester Vedsted. The water rose to just 30 cm from the top of the Ribe Dike.

Future storm surgesThe Intergovernmental Panel on Climate Change (IPCC) predicts a warmer climate, which will incre-ase the number of future storms on our latitudes. The dikes are therefore under pressure and the towns alongside the Wadden Sea confronted with huge challenges.

The number of storm surges with sea levels of bet-ween 2 - 3 meters have, according to statements going back to 1872 from Esbjerg Harbor office, more than tripled in the last four decades and at the same time, from 1975 - 1999 we have experienced the

strongest storm surges since the 1634 storm surge with sea levels of up to 5 meters.

As well, the IPCC expects the sea level to rise 9 - 88 cm over the next 100 years, and with a rise of 11cm during the last 100 years, the question is whether our dikes alongside the Wadden Sea coast are se-cure enough.

Today, there are dikes on most of the almost 500km long stretch from Ho Bugt and Esbjerg in the north to Den Helder in Holland to the south

1362 The Great Drowning1634 The Second Great Drowning1911 The last storm surge that reached Ribe 1923 The last time anyone drowned during a

storm surge in Denmark1953 1800 people perish in the Netherlands1962 350 people perish in Hamburg1968 Iced up river with 4.35m DNN packed ice by

Ribe Kammersluse1976 The dikes are severely damaged.

Radio becomes part of the Storm Surge Preparedness

1981 The Mandø dikes destroyed. 200 sheep and 18 head of cattle drown

1999 The worst hurricane ever recorded in Denmark

the worSt Storm SurgeS

Klaus Melbye, Vadehavscentret & Anne-Marie Overgaard, Museum Sønderjylland

tide & lAndScApe

translation: nanna Mercer, Sirius translationpage 4 of 4

Experience the Storm Surge Show at Vadehavscen-tret.

Visit the storm surge pillar by: • Janderup Ladeplads• Ribe Skibbro• Mandø beach• Mandø Ebbevej• Sønderho • Nordby• Marskmandshuset in Ballum Enge• Vidå Slusen• Højer Gamle Sluse

thingS to do

NaturKulturVarde Gl. Skovfogedbolig Roustvej 111 DK-6800 VardeT: +45 75 22 22 50E: [email protected] W: www.naturkulturvarde.dk

VadehavscentretOkholmvej 5 Vester Vedsted DK-6760 RibeT: +45 75 44 61 61E: [email protected] W: www.vadehavscentret.dk

Naturcentret TønnisgårdHavnebyvej 30 DK-6792 RømøT: +45 74 75 52 57E: [email protected] W: www.tonnisgaard.dk

Museum Sønderjylland - Højer MølleMøllegade 13 DK-6280 HøjerT: +45 75 44 61 61E: [email protected] W: www.museum-sonderjylland.dk/hojer-molle.html

Learn about Storm SurgeS here ...

Read Theodor Storm’s 1898 work The Rider on the White Horse and selected stories translated from the German by James Wright, about the farm boy Hauke who becomes dike master and then builds a new dike. About storm surges, ghosts, marshland peasants and passions.

hoLiday fiction?

Vadehavets Formidlerforum is a partnership of visitor centers that mediate the Wadden Sea’s natural and cultural heritage. VFF’s main activity is to coordinate projects that highlight the nature and culture heritage of the Wadden Sea..Learn more at www.vadehav.dk

about VadehaVetS formidLerforum...

The salt meadows in the Wadden SeaThe Tide and the Wadden SeaThe Wadden Sea LandscapeLife on the waddens

tipS for further reading ...