Dry, hot summers put Dutch dikes at risk

It was 2 a.m. when the floodwaters came, inundating an entire residential area in the village of Wilnis, near the Dutch city of Utrecht. Some 1,500 people had to be evacuated.

An old dike had broken over a length of 60 meters (around 200 feet). It was the middle of summer — August 26, 2003 — not during a winter storm, when such an incident is more likely.

But it was a very dry summer, and specialists quickly understood that the dike had literally dried out. It had lost its weight and stability and had simply not been able to withstand the river water.

Hundreds of kilometers of dikes in the country are built out of peat, which acts like a sponge. If it gets too dry, it becomes light and porous — and dangerous.

Checking dike after dike

So far this year the dikes have all held, despite the heat. But Dutch authorities have put a drought emergency plan into effect, which also includes increased controls on the dikes.

"The drought causes some holes and cracks in the surface. This can be dangerous for the stability of the dikes," said Arjan Goossen from the water management authority in Zeeland, a province in the country's south.

Specialists and volunteers are now checking the dikes for cracks. "We know the weak spots and look with our bare eyes," Goossen told DW. "What we do is monitor the cracks. Normally in the autumn, when the rainy season starts they would fill up again. If not, we fill them up."

Irrigating the large dikes in Zeeland, which are supposed to hold off the waves of the North Sea, would make little sense at this stage, he explained. They are so dry that water would simply fizzle out in the summer heat.

The dikes that are directly at the coast are not made of peat, but rather of earth and clay. They cannot break as easily but in winter, when the storm surges come and the sea gnaws at the structures, cracks have to be filled up again. "We will have a lot of work in the autumn," predicted Goossen.

Watering the dikes

Smaller dikes made of peat and built mainly inland, along canals and rivers, are irrigated with special boats, which pump water from the canals onto the embankments.

They are being deployed more and more frequently, with the country experiencing droughts in 2018, 2019 and 2020. There hasn't been enough rain to water the dikes and fully replenish the groundwater. Farmers in the south of the Netherlands are no longer allowed to use water from canals and rivers to irrigate their fields.

Agriculture is essential for the Netherlands, but this year farmers' associations fear the harvest will be poor. They are already at loggerheads with the government over forthcoming restrictions on pesticides.

"The Netherlands is a country of water. And water is very precious here," said Mark Harbers, the minister for water management, when the government declared a state of emergency last week. "The priority now is that the vital dikes remain safe. After that comes the drinking water and then the energy supply."

Two-thirds of the population live in regions below sea level. Rotterdam and Amsterdam would be flooded without intact dikes and pumping systems. In Amsterdam, city workers use fire hoses to keep the dams moist and thus heavy enough to hold back the water.

Building higher dikes to counter climate change

In Zeeland, right by the sea, the rising sea level is the biggest problem. Due to global warming and melting ice at the Earth's poles, the pressure on the dikes is increasing each year.

"We are therefore carrying out a program to strengthen them. We are making the dikes stronger and higher against climate change," explained Goossen. But the basic design isn't being changed.

For years, water management authorities in the country have observed that there hasn't been enough rain to replenish the water system. This is also leading to salinization of the groundwater and affecting shipping. The use of many locks has had to be restricted this summer, because the sea is pushing saltwater into the rivers.

So far, the Netherlands has relied on regular rainfall — the country has no underground water reservoirs in caverns or large reservoirs that would work as a retention system. That might have to change in future.

Several proposals have been made: Either underground storage for rainwater should be built, or distributaries of the Rhine, which flows from Germany into the North Sea near Rotterdam, should be used.

However, it won't be easy to find the space in the Netherlands, which is so densely populated. 

This article has been translated from German