In recent years, the soil in the peatlands of the western and northern Netherlands has subsided more quickly than before, according to a new soil subsidence map by researchers at TU Delft. In addition, the new map makes it clear that sandy soils in the north and east of the country are also starting to subside due to the falling groundwater level.
This subsidence causes damage to subsiding streets, bridges, sewers and other pipes, in short, everything that is placed in the public space of tax money. In 2016, the Netherlands Environmental Assessment Agency estimated this subsidence damage at 2 to 6 billion euros for the next thirty years.
According to lead researcher Gert Jan van den Born, that estimate would now be considerably higher. ‘More and more areas are affected by subsidence, the desiccation is forcing us to carry out repairs more quickly and building has become more expensive.’
1 million homes
The damage to homes is also higher than previously thought: 80 billion euros. ‘We estimate that one million homes will have to be rebuilt in the next thirty years, for an average price tag of 80,000 euros each,’ calculates Dick de Jong, director of the government foundation Kenniscentrum Aanpak Funderingsproblematiek (KCAF).
‘It will soon become critical for many old city and village centers on the peat soils in the Green Heart and in Friesland,’ fears Professor Ramon Hanssen, one of the authors of the map. In those areas more and more houses are sagging, heralded by cracks in the walls and skewed window frames and doors. The wooden posts on which most of these buildings rest also rot when they dry up and crumble.
The greatest risk are homes in peat meadow areas built before 1970, because they are often built on wooden stilts. In the past, the KCAF mainly received reports of subsidence from Gouda, Amsterdam, Rotterdam, Haarlem and Dordrecht, peat areas where construction is traditionally built on wooden piles. In the past three dry summers, however, the soil also started to shift on sandy soils and in the river area.
Homeowners
De Jong: ‘Two years ago there were about sixty municipalities from which residents came to us with foundation problems. The alarm signals are now coming from one hundred and eighty municipalities, that is half of the country. If we get three more such dry summers, I hold my heart. ‘
Although the damage is caused by the drop in groundwater levels in an entire area, the costs are borne by individual homeowners. ‘These are often very sad situations,’ says De Jong. ‘People who have put their heart and soul into a house, and are then told by us that they have to lay a new foundation for eighty thousand euros. While they don’t have that money at all. ‘
In the past year, KCAF received almost fourteen hundred reports of subsiding homes, twice as many as three years ago. According to the law, municipal responsibility for groundwater management ends with the residential area and most municipalities therefore hardly support residents with subsided buildings. And although appraisers are legally obliged to check the foundation risks when a sale is made, that often falls short. That is why many homeowners who suspect foundation problems prefer not to report this on the big clock: half of the reports to the KCAF are anonymous.
Municipalities
Municipalities could do much more to assist their residents in this, says De Jong. The KCAF, in collaboration with the National Mortgage Guarantee, has set up the Sustainable Foundation Repair Fund, from which residents can borrow to restore their foundations, but only a handful of municipalities are affiliated with this. ‘The government should take up this responsibility. Municipalities have a role to play in supporting residents in risk scans and foundation restoration, but lack the financial strength to make a significant contribution to the new foundations themselves. ‘
A spokesperson for the Association of Dutch Municipalities (VNG) points out that some municipalities are indeed taking action. Woerden, for example, has an action plan against subsidence. In addition, the VNG states that provinces and water boards also bear a responsibility to prevent pile rot and subsidence with good groundwater management.
New subsidence map provides precision image
The new soil subsidence map from the Netherlands Center for Geodesy, SkyGeo and TU Delft not only offers new insight into national developments, but also an unprecedented level of detail. This allows governments to keep an eye on individual highways, bridges, railway lines and power plants, and, for example, all 17,000 kilometers of dike in the Netherlands.
Hanssen: ‘We know that many of those dikes need to be replaced, but the question is: which ones?’ Surveyors can only check a small area at a time. While the bottom is different everywhere: while one part is subsiding, the dike a little further away can be fine. With this map you can check such an entire dike in one go.
Everywhere in the Netherlands the soil subsides, rises, shrinks, swells and shifts in different ways, leading to problems for buildings and infrastructure. Hanssen zooms in on a random piece of the map: ‘Look, a railway near Utrecht is sinking here. This dredging depot at IJmuiden is just rising. And here, on the A1 near Diemen, one lane drops away while the other stays neatly in place, you see? That will soon be grinding. ‘
On bodemdalingskaart.nl citizens and governments can view the map themselves and download the underlying data.
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More about drought in the Netherlands
Her house became ‘a ramp.’ Urban planner Riek Bakker knows what subsidence does
1 millimeter per year, that seemed to landscape architect Riek Bakker to be a subsidence that was manageable when she bought a farm. Until the cracks appeared and everything had to be demolished.
Is it time for wetter meadows?
In order to combat soil subsidence and CO2 emissions, it is time for the national government to seriously work on the rewetting of peat meadows. Herman Lenes, who farms on peat soil in Friesland, is considering participating in a project, but is also cautious. ‘If it gets too wet, your growing season can suddenly be ruined.’
Why is central government doing so little about soil subsidence and CO2 emissions in peat meadow areas?
In the peat meadow areas, the soil subsides annually by almost one centimeter and a lot of CO2 is released due to the artificially low water level. High time for action, experts say politicians have been postponing this problem for decades, concludes the Council for the Living Environment and Infrastructure.
Dossier: The ‘assassin’ called drought
Wildfires, failed harvests, broken dikes and endangered species. The Netherlands is ravaged by drought. De Volkskrant In this dossier, examines what the consequences are, how things could have come to this – and how the drought can be resolved.
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