The Kystdirektoratet is investigating a 63 kilometer long dike on Lolland, which could provide important information.

Danish dikes must be secured against flooding, and therefore residents of Lolland can see machines running around and taking samples at the dikes.

The Danish Coast Directorate is actively conducting bore samples to determine what lies within the dikes. According to the directorate's office chief, Thorsten Piontkowitz, they want "a little more knowledge about the resistance and strength of the Danish dikes, and the dike's composition plays a central role in this."

The ideal composition they hope to find is dikes built with a sand core and a layer of clay around it, which protects against intruding water, followed by topsoil and grass that keeps everything in place. However, it is far from certain that the samples will show this.

"The construction of the dike is quite important, in terms of how strongly it stands in a storm surge situation," Piontkowitz said.

Some of the dikes date back to 1872. This is according to the chairman of The Lolland Dike Association, Henrik Marcussen. In 1872, a storm flood cost 81 lives at Lolland and Falster, and work began on building a dike.

"They were built after 1872 with the materials available at the time, and there may be places where there wasn't much clay, where other materials had to be used instead," Marcussen said.

When Frederikssund prepared for storm Malik in 2022, they laid water tubes to protect Kronprins Frederiks Bridge against the rising water level. (Photo: © Mads Claus Rasmussen/Ritzau Scanpix)

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Exploring dikes on a combined 240 kilometer

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It is the engineering company Geo that is conducting the borings for the Coast Directorate, and they are about halfway through on Lolland. In total, there will be approximately 139 borings along the 63 kilometer long dike.

And in addition to the dikes along the Lolland coast, approximately 240 kilometers of dikes will be explored in other parts of Denmark - including Fanø-Esbjerg, Nordfyn, Randers, and dikes near Juelsminde and Vordingborg.

There are a total of 1,100 kilometers of dikes in Denmark, according to the Coast Directorate, but it is the dikes with the least information that are currently being tested.

The dikes are being tested by the engineering company Geo using bore samples, which are taken using a machine called a minirig, as seen in the photo. (Photo: © Coast Directorate.)

Approximately half of the borings have been completed, which began in May.

"It's important because the construction of the dike is quite important, in terms of how strongly it stands in a storm surge situation," Piontkowitz said.

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Climate change sets new demands for dikes

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The dikes were previously typically built by local farmers with the materials that were no longer available, and it may have worked well with the old wind and weather.

But due to the more extreme weather caused by climate change, the old dikes may be put to the test, according to Piontkowitz.

"We risk having the dikes fail during a major event, and having a dike breach where water rushes into an area and floods it," he said.

42 million kroner was set aside in the 2023 budget for the Coast Directorate to map out the dike's composition.

"It's important that we find out what it takes to withstand future influences," Marcussen, chairman of The Lolland Dike Association, said.

The Coast Directorate is also developing a model where the collected data is combined with other data to calculate how strong each dike can withstand various events, such as powerful storm surges, and what improvements may be necessary to make them more resilient.

"The model will be made available to the dike associations or municipalities, who can determine whether the strength is sufficient or if there needs to be reinforcement of the dikes," Piontkowitz said.

A water tube could not hold back the water in Aabenraa during the storm surge night between October 20 and 21 last year, where up to 70 houses were flooded. Read also: Vejle and Nakskov are bracing themselves, how expensive it is to protect the coast (https://www.dr.dk/nyheder/indland/vejle-og-nakskov-bakser-med-hvor-hundedyrt-det-er-sikre-kysten)

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Association wants a national standard

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One who is waiting for the results of the tests is the chairman of the Danish Dike Association, Bent Alminde.

"It's necessary that we find out if there are dikes in Denmark that are not ready to withstand the weather we have today. I hope that such a mapping can provide an answer," he said.

He also hopes that there will be a national standard for coastal protection when the Coast Directorate's results are available.

"If there is a standard that, for example, says that dikes should be able to withstand 100-year events in 2050, then the municipalities and dike associations know which standard to follow, and I think that's necessary," Alminde said.

Alminde, who is also vice chairman of The Lolland Dike Association, also believes that there should be a national action plan to secure the coasts.

"We have protected ourselves as best we can, but we must also look ahead, and that's why we will be forced to have a national action plan where the Coast Directorate and the state are also involved," Marcussen said.

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