Land subsidence in the Netherlands
I usually only blog when I’m on field trips, not when I’m going to a conference. This time, however, the meeting was the 10th International Land Subsidence Symposium (TISOLS), held in Delft and Gouda, the Netherlands. In addition to meeting other people working on land subsidence around the world, I also learned and learned more about how the Dutch transformed their country so that about 1/4 of its land area is below sea level. As they say: “God made the earth, but the Dutch made Holland”.
Sign at the former peat dig site Schiphol Airport.
A famous graph shows how, over the past 1,000 years, multiple human interventions have caused the land in the Netherlands to sink due to rising sea levels.
The story begins about 1000 years ago with the invention of the bulldozing plow or dieboard plow. It turns the organic-rich peat soils of the Netherlands. To improve drainage, the Dutch began digging channels.However, draining the land exposes the peat to the air, where they are oxidized, converting much of the soil into carbon dioxide2 and water. Land subsidence led to deeper and larger channels, which were then pumped by windmills. They also mined peat for fuel. The deepest areas are where peat was mined in the past. Some are 22 feet below sea level. The low-lying areas are preferably grasslands leading to the cattle industry and the Dutch cheese industry. The dikes, cheese and windmills in the Netherlands are all the result of land subsidence.
See Wageningen’s windmills, which are still used to grind wheat into flour.
I started my journey in Wageningen, in the middle of the country, where I wrote a paper with several colleagues, Carol Wilson of LSU, Steve Goodbred of Vanderbilt University, and Liz Chamberlain of Wageningen University. papers on Bangladesh. We also visited a windmill near the historic city center that is still used to grind flour. Carol and I also cycled to Nederrijn (Lower Rhine). We walk across the dikes that protect the town and see open pastures that protect the city by containing any flooding.
Earth embankment protecting Wageningen from floods. On the slope ahead there were sheep grazing.
3D model of the Netherlands terrain. Yellow to light green is land below sea level. The model has a high altitude cutoff of 40 m (131 ft).
After spending the weekend in Wageningen, Carol and I headed to the canal-laden city of Delft for the TISOLS conference. Our hotel is in the old town. Consisting of 4 old buildings, I had to walk up and down multiple stairs to get to my room as each building was on a different floor. We walked 20 minutes to the University for a conference.
One of Delft’s many canals can be seen from my hotel room.
We had demos and poster presentations on Mondays, Wednesdays and Thursdays. I will be presenting my research on subsidence in Bangladesh on Thursday. On Tuesday, we did a number of field trips. I joined Zegveld in the middle of the western Dutch settlement. The first stop is an old peat digging area, now a group of lakes. It has been turned into a nature reserve and perhaps new peat is being planted to reclaim the land.
An old peat dig site has been transformed into a well-preserved wetland.
Auger samples showing peaty (highly organic) soils in the Netherlands.
Next stop is the Environmental Research Station and Farm. Here they have equipment to measure land subsidence and sediment compaction, CO2 and methane emissions, and can be tested with different water levels and crops. I want to install something they have in Bangladesh. After a Dutch lunch of soup and cheese sandwiches, we headed to the villages of Kanis and Kamerik. This concludes our introduction to the problem of urban and rural land subsidence.
GNSS antenna and InSAR corner cube for monitoring elevation changes. Carbon dioxide and methane monitoring equipment can be seen in the background.
We learned that many buildings are built on different piles. The shallower ones may end up in oxidized peat, the deeper ones in the hard sand below. Some are wooden and will rot if exposed to the air, newer ones are concrete. In the 19th century church, thick mounds kept it from sinking, but the roads and parking lot were sinking. The village road was recently raised to compensate. However, the weight of a meter of new material can cause compaction of the peat below.
Due to land subsidence, the doors of the church are now high off the ground.
They cannot stop the ongoing land subsidence in the Netherlands, they can only control it, try to keep it to 3-5 mm/year. The country’s water levels are tightly controlled by water boards elected by the people since the 1400s. They are the oldest democratic institution in the country. Everywhere there is a balance of keeping water levels low to prevent flooding and keeping water levels high to prevent subsidence.
Signing up for Subsidence and Society Day in Gouda, it is important to understand land subsidence.
The importance of this issue was highlighted on Friday when we went to the historic Sint Jans Church in the town center of Gouda for a Day of Settlement and Society. The church itself is distorted by the different settlements on its sides. There are presentations and lectures, interviews and panel discussions. A focal point is the Kenniscentrum Bodemdaling en Funderingen (www.kbf.nl) or Gouda’s Land Subsidence and Foundations Knowledge Center. This is unimaginable outside the Netherlands, a country whose name means low-lying land.
Meeting inside Gouda Cathedral.
A stained glass window depicts the Spaniards lifting the siege of Leiden in 1574 by breaking dikes and flooding the area and bringing in the Dutch fleet from sea.
The day ended with a walking tour where we visited the old buildings and canals of the city. The land along the river, with its sandy sediments, is much higher than the peat and sediment-built parts of the Old Town. The current plan, not popular with all, is to hydrologically isolate part of the old town with locks and pumps to lower the water level by about 10 inches.
The canal is the low elevation part of Gouda, where the water is almost at street level on dry days.
The river shuts it with its locks. The ground here is much higher due to the sandy deposits next to the river. Both photos have the same water level.
While this is a scientific conference, the field trip and drop day deserves a blog post about it. Spend the entire week at or below sea level. Between sinking land and rising sea levels, many more areas will soon be below sea level. It’s impressive how much of the Netherlands’ water is an actively managed system, with water levels carefully controlled by dikes, locks and pumps. It is only because the Netherlands is a rich country that it is able to maintain so much land below sea level.
Gundam old house deformed by land subsidence.
