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What is “flood risk”?

Risk situations.
Risk situations.
Source: Rijkswaterstaat, The Netherlands

There are different types of floods. However, all floods begin with a hazard. A fierce storm is a hazard. The storm drives up the sea and caused high waves that hit the coast. A hazard does not always lead to a disaster. If the country is high enough or if it is well protected by dikes and dunes, then the storm does not lead to a flood. If the sea water flows over the protection, or breaches the dikes or dunes, than the land behind it will be subject to flooding.

Risk is a combination of probability and consequences. The Dutch national water authority “Rijkswaterstaat” uses this drawing to the right to explain the concept of risk. The consequences may be victims and damage to homes, businesses and nature.

If the probability of a major flood is high and the consequences are severe you speak of a “high” risk. For instance when a flood would cause many victims and there would be a lot of damage. If the probability of a flood is small and the consequences are too small then the risk is also “small”. These situations are clear.

The other two situations are less clear. What risk do you think is worse? Floods that can happen often with small consequences, or floods that happen very seldom, but with very serious consequences? You can calculate risk by using various methods, but whatever method you use the question remains: what is the risk we are willing to accept?

In which of these four categories would you to say the risk in your country or your part of the country is? Why do you say so? Use an elevation map, a map with a map showing land use and a map with population density to explain your answer.

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