It is said that the cold snap in Germany could help in the fight against flood damage to dikes. But homeowners in flood zones fear the frost. The matter is complex.
The flooding is causing hardship for many people in Germany. Now the frost is coming – and with it the hope that the cold could give the dikes in particular more stability. Is that safe? And what do the sub-zero temperatures mean for agriculture, animals and buildings in flood areas?
Dikes
It cannot be said in general to what extent frost has a positive or negative effect on dike stability, says Anne Rickmeyer, director of the Lower Saxony State Office for Water Management, Coastal and Nature Conservation (NLWKN), to the German Press Agency. Therefore, their advice is: The situation on the dikes must continue to be monitored closely. “The individual case must always be considered here. To maintain flood protection, weather conditions must always be taken into account and are only one component in the overall assessment of the situation.”
Frost can have a positive effect
If a dike is exposed to frost without any water effect, the soil will solidify at a certain depth – depending on the temperatures and the duration. “This can have a positive effect on stability and tightness if water accumulates.”
However, the situation is currently different in many places: water levels are still high in some places and masses of water are pushing against dikes. “If there is relatively warm water on the dike before the frost period, the area below the water level will not freeze and no positive effects will occur there.” Above the water, however, the earth’s surface of the dike will freeze and prevent further precipitation from penetrating. “That would then be seen as positive.”
Agriculture
Flood plus frost – you also have to differentiate carefully when it comes to the consequences for agriculture. “Frost is usually a blessing for our soils,” says Prof. Christoph Tebbe from the Thünen Institute for Biodiversity in Braunschweig. The normal winter frost is good because it loosens the ground. “Our soils need frost.” But things look different when the arable land is completely submerged in water at very low temperatures, explains Tebbe. “The soil then doesn’t regenerate over the winter and it is too dense.” It would then no longer be able to absorb as much water in the spring. Ultimately, this could affect harvests.
Floods
Flooded streets, emergency dikes, constant rain warning: pictures from the flood areas
Animals
The environmental foundation WWF (World Wide Fund For Nature) is not worried about the animals and plants in the flooded areas – even when there is frost. “Animals and plants have adapted to flooding in their habitats,” says Albert Wotke, WWF expert for area nature conservation, to the German Press Agency. “There are also losses.” This is not unusual and is a “natural situation”. After all, floods have always existed.
But the floods are tragic for the people affected. “The problem is that approved houses are in areas where they actually shouldn’t have been built,” reports Wotke. In this context, he complains about “flood dementia”: At first there is great excitement during floods and after six months a lot of things have often been forgotten.
Building
Homeowners in particular fear the combination of flooding and frost. The masonry can be damaged if it is damp. “When water freezes, it expands by ten percent,” says Prof. Norbert Gebbeken, an expert in structural engineering at the Bundeswehr University in Munich. “And this expansion can create such a high pressure that material or components are really destroyed” – especially if parts of the building are already soaked with moisture. When temperatures are around ten degrees below zero, homeowners have to try not to let the cold penetrate into wet parts of the building, for example with bales of straw or thermal insulation panels from the hardware store.
Homeowners should pump out basements during floods
However: “Moderate and not long-lasting frost will not cause standing water in the basement to freeze,” says Christine Buddenbohm from the Central Association of the German Building Industry. The depth to which frost penetrates is deeper in the mountainous south than in the north. In the middle of Germany it is 80 centimeters. Homeowners should still pump out full basements if possible, but at the same time take other risks into account.
Carelessness
The expected freezing temperatures could cause locally flooded areas to freeze. The fire department warns against entering such ice surfaces or even taking out your skates there. “‘Looks good’ is not an indicator that the ice is stable,” said Jörg Rühle, spokesman for the Hanover fire department. Rühle expects that the ice surfaces could also attract careless people.
Over the past two weeks, careless people have repeatedly been spotted traveling in flood areas on kiteboards or canoes. “This is of course life-threatening,” said Rühle. The authorities constantly warn against going into flood areas. Since the flood began, there have been more water rescue operations. The exact number was not known.
emergency services
Cold can also be stressful for people – but the Federal Agency for Technical Relief (THW) does not expect any major problems for its emergency services in Lower Saxony due to the expected sub-zero temperatures. “Despite the falling temperatures, we have no worries about our emergency services at the moment,” said a spokeswoman for the THW in Lower Saxony. All helpers are accommodated on site in permanent and heated accommodation. Their clothing is suitable for all weather conditions and can, for example, be made even more cold-resistant with special fleece inserts. “If it gets colder over a longer period of time, the shifts of the emergency services could also be shortened. However, this is not yet on the cards,” said the spokeswoman.
Bundeswehr partly in action
For the first time in the current flood situation, soldiers from the Bundeswehr are on duty. Around 200 temporary and professional soldiers have been helping to fill and distribute sandbags in the Mansfeld-Südharz district in the south of Saxony-Anhalt since Friday, a spokeswoman for the Bundeswehr said. The initial aim is to stabilize a section of the dike in Sangerhausen. The water has been pushing against the dike there for days.
Due to the tense flood situation in Lower Saxony, Bundeswehr helicopters are still on standby to provide assistance from the air. According to the state command, this involves a total of ten machines from the army, navy and air force, which are spread across several locations in the state. If an operation is necessary, the helicopters could, for example, support evacuations and the transport of heavy sandbags.
In Bremen, for example, where there is a warning of major flooding in the Wümme area, the situation remained rather static on Saturday night, according to the fire department. There were no corresponding operations. Nevertheless, one cannot speak of a relaxed situation, said a spokesman.
The water levels on rivers in Lower Saxony could fall in the coming days. A tendency towards falling water levels is expected, said Anne Rickmeyer, director of the state agency for water management, coastal and nature conservation. However, it could still take several days or even a week until the water levels are below the more critical ones.