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Water Levels As Public Data

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The West-European storm of last week managed to push even COVID news out of the picture, it was that ravaging. In multiple villages and cities in Wallonia, only thirty something kilometers from where we live, solid stone facades of houses even collapsed due to the raw pressure of the water. The water level rose to more than two meters high, people climbed roofs to wait for help while watching their cars, fridges, and sofas rush past in the strong current of the ever growing water. For 31 Belgians, it was too late. Many people are still missing. In parts of the Netherlands and Germany, the havoc is even worse. While parts of Oregon are burning up, we’re drowning here.

Last week was devastating. Whole villages are utterly destroyed. Roads crumbled, houses collapsed, and all possessions wrecked due to the high water and mud levels. Something experts said has never before been seen this century. We were lucky, the local river the Demer just about held it together. This picture was taken 100 meters from our house, at the 15th on 9h00:

Can you spot the bridge? Only two fingers removed from a disastrous flood...

Heavy rainfall is not particularly something we Belgians aren’t used to, but persistent rainfall of more than 8 mm every ten minutes is what we’d call extreme. To learn more about the difference between rain intensity and amount, I dug up our trusty weatherman’s website

Precipitation is measured in millimeters. One millimeter of precipitation corresponds to 1 liter of water per square meter. If one liter of water is poured onto 1 square meter and that water does not evaporate or seep into the soil, it is 1 mm high.

To measure intensity, the amount of millimeters is added up over a period of time, say 24 or 48 hours. The huge amount of rainfall in a short period of time on the 14th and 15th of July is called a water bomb. Frank’s website is also filled to the brim with measurement graphs from Ukkel. Strangely enough, the official KMI website (Koninklijk Meteorologisch Instituut or Royal Meteorological Institute) contains less useful information. For Flanders, public rainfall and water level data is accessible through

Not far from the bridge in the above photo, an indication in the concrete allows you to read the local Demer water level. Although the database seemingly contains information about two measurement points in our village, the data returns NaN and the CSV is empty. A pilot project is being set up, the data should start flowing in next year. Meanwhile, I took the opportunity to carry out a few rudimentary measurements (just after the small waterfall):

  • 14/07, 19:49h: 27.7 m
  • 15/07, 09:30h: 28.3 m
  • 21/07, 11:01h: 26.7 m1.6 m, and still going down!)

Station ID L09_136—according to the friendly people at VMM at the Kiezelstraat in Hasselt on the border with Diepenbeek—does contain water level data from 1982 and beyond. You can download the raw data yourself of fiddle with the settings of the following graph, displaying water levels form 21/07/2020 to 21/07/2021:

It is great to see that this information is readily accessible, although a bit on the clunky side. I was curious how difficult this was going to be after reading Peter’s radar sign data access request story in Canada, where the data is hidden behind both a paywall (although little) and an administrative queue. VMM (Vlaamse Milieu Maatschappij or Flemish Environmental Society) also provides detailed yearly flood reports, full of fancy graphics. The water bomb hit Wallonia the hardest though, and that data is of course not available on Another reason to unify our already too divided country…

The data reveals other great floods, also summarized at, of which the storm in November 2010 was the last one—only then, Wallonia/Liège was mostly spared. The article also contains pictures of the overflowed Maas in Dinant at January 1995. Embarrassing newspaper article headlines such as “Severe weather November 2010 costs insurers 104 million euros” ( reduce misfortune to financial numbers.

Geese prove that today the water is navigable again. The forecast declares a few more days of respite before the inevitable rain returns.

Those who wonder how many euros July of 2021 is going to cost should re-read how many people have lost their homes and lives.

tags icon Hasselt datavis

In reply to Water Levels As Public Data by Wouter Groeneveld You might try the European INSPIRE portal to see if there’s any water data there that covers la Wallonie. It wouldn’t be the first time that data which isn’t available locally is prov...

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I'm Wouter Groeneveld, a Brain Baker, and I love the smell of freshly baked thoughts (and bread) in the morning. I sometimes convince others to bake their brain (and bread) too.

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