Flooding is possible at high water levels. One of the reasons for this is that the countryside around the Rhine is increasingly being used by people. Building houses, factories and offices leaves less and less space for the river. The water gets higher. Take a wide dish and pour some water into it. Pour that water into a narrow glass. The water level in the glass will be higher.
less space, higher water level
Smaller opening, stronger water jet
Water cannot flow away in a glass, but in a river it can. If the river has less space to flow, the water has to be carried along more quickly. The river flows faster. But think about what happens when you pinch a garden hose. The water has to pass through a smaller opening, and the stream becomes stronger. The water in the Rhine is now flowing more than twice as fast as in the past!
Briefly, because we give the rive less space, the water is flowing fast and water levels are rising.
Cultivated landscape
Landscape that has been shaped by people is called a cultivated landscape. Over the years, the catchment area has become more of a cultivated landscape.
The area around the Rhine is used for farming, and there are houses and factories along the river. Dikes have been built at many points to protect these areas against the water. Dikes are also part of a cultivated landscape.
Natural landscape
A landscape that is entirely shaped by nature is called a natural landscape. For example, woods and lakes. The catchment area used to contain more natural landscape. At that time, a lot of extra water could remain behind in the area around the Rhine. And it didn’t matter if they flooded occasionally!
Precipitation that falls in areas that have been left to nature remains on the ground for a while or slowly seeps into it. It takes a while for it to reach the river. But in areas where people have built houses the water is quickly removed by drainpipes and sewers, for example. This means that rain which falls in a cultivated landscape usually reaches the river more quickly!
Areas prone to flooding
In a natural landscape, there are areas which have always been prone to flooding. We call them ‘flood-prone areas’.
Not all the flood-prone areas we have now are natural. They were often due partly to human intervention, for instance the building of a summer dike and a winter dike. The low dike close to the river is called the summer dike, and water rarely gets further than this dike in summer. In winter, water levels are higher and water flows past this dike. This is why there is a higher dike further on, called the winter dike. The area between the two dikes is called the artificial flood plain. This is an area deliberately left for flooding. At high water it floods because there is enough space for water here.
There are fewer artificial flood plains in the Rhineland than there used to be, and those which do remain are smaller, because we have built on them. Have a look at the maps of the Rhine north of Breisach in Germany.
[Translate to en:] De Rijn ten noorden van Breisach (DE) (Beeld: Landesvermessungsamt Baden-Württemberg)
1. Floodplain 2. River bed 3. Wetland A. Overflow dam B. Main dam