A precipitation bomb such as the one that hit the Limburg hills in the summer of 2021 will fall more often in the future. Moreover, there are no simple measures to prevent such rainfall from causing similar problems as then. Those conclusions can be drawn from a new research report. The message: learn to live with floods.
Back to July 2021. Sudden heavy rainfall in the south of Limburg, the Belgian Ardennes and the German Eifel led to an enormous supply of water in streams and rivers. In some places in the Ardennes, no less than 250 millimeters fell in two days, but near the Caumerbeek in Heerlen it was also a hit with 175 millimeters. To give you an idea: that is as much rain as normally falls in two to three months.
The precipitation led to severe flooding, which killed several hundred people in Germany and Belgium and caused at least 440 million euros in damage in the Netherlands alone. The fact that there were no casualties in our country is more luck than wisdom, concludes Deltares, the Delft research agency that has been investigating the floods for the past eighteen months.
Extremely tricky
“Given the circumstances, that could certainly have been done,” said researcher Nathalie Asselman on Thursday at the presentation of the report. For example, in Valkenburg, the most affected place, the situation near the Geul was at one point extremely precarious, according to a detailed reconstruction made by Deltares. In other places in the hills, people were also hit by suddenly rising water.
The first question that the researchers, commissioned by the province and the water board in Limburg, have tried to answer is how unique these events were exactly. The KNMI calculated that rainfall such as this can now occur once every five hundred years. However, an important nuance: due to climate change, this will go towards once every hundred years this century. The Belgian meteorological institute, the RMI, even thinks that that probability level has already been reached.
In short: the chance that the Limburgers will be confronted with such a natural disaster again is increasing. This makes the other question that Deltares answers in its report – what measures are possible to prevent such a deluge from causing so much damage again – even more relevant.
However, the conclusions are not very reassuring. “The prevailing image is that it will be very difficult to significantly reduce the risk of flooding in the entire catchment area,” writes Deltares. “The measures required for this in the water system are often too large, too expensive or too far-reaching.”
Metre-high wall
An example: to prevent the old center of Valkenburg from being flooded again, a wall of three and a half meters high would have to be built in the center. Another option – increasing the capacity of the Geul, the stream that flows through the town – would mean that an unknown number of houses would have to be demolished. Both are not attractive options for Valkenburg, which is the tourist attraction of the hilly area – quite apart from the question of how much it will all cost.
In their study, the researchers state that some measures are possible. In any case, they help to dampen the effects of new torrential rains. For example, the landscape can be adapted in such a way that more water is absorbed into the soil, and more storage can be created to store water.
However, it only helps to a limited extent, says Asselman. “The first option can theoretically lower the water level by 5 to 20 centimetres, but in Valkenburg there was 120 centimetres. And more storage options may provide an extra capacity of 1 million cubic meters, but ten million cubic meters would have been needed to keep Valkenburg dry.”
Learning to live with high water
The lesson: the Limburg hills will have to learn to live with the possibility of high water. This affects the way houses are built – they should no longer be located in places where there is a high risk of flooding. Residents of the area must also be better informed when danger threatens. Asselman: ,,Now they were told that there was danger, but they didn’t really know what to do. Just shouting that it’s code orange doesn’t tell people enough. Do you have sandbags ready? Do you have to leave your house? Residents really need to know what a certain situation means to them.”
The results of the study are used by the province and the water board in Limburg for the Flood Safety and Spatial Planning Limburg programme. The aim of this is to better protect the inhabitants of Limburg and to prepare them for the consequences of extreme weather.
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