In the Netherlands, the term flooding is used if too much water causes fields, streets, tunnels and cellars to flood. Flooding is caused by excessive rainfall which cannot be absorbed quickly enough through the soil or which cannot be discharged via the sewer of via the waterways. Causes can include extensive rainfall or a large downpour in a very short space of time.
The Dutch sewer system can only cope with a certain amount of rainwater. In fact the sewers are intended mainly for the discharge of waste water and enlarging the sewer system would cost a lot of money. The remaining rainwater therefore has to be absorbed into the soil.
In order to prevent flooding in the event of lengthy rainfall it is important that the water can seep down into the soil. This can be achieved by planting more greenery (such as grass or shrubs) or by laying permeable paving. Where necessary, the water boards will remove the water, for example via pumping stations.
The problem with heavy downpours is that so much rain falls in such a short space of time that the water cannot be entirely absorbed into the soil. Sewers can often remove some of the water, but not all of it. The water then flows across the surface to the lowest point in the landscape. In order to prevent flooding, it is important that the water can flow to somewhere where it does not cause any problems. Examples are ponds, green play areas, wadis and water squares where the water can be stored temporarily. Although these areas are usually dry, rain water can flow into them during heavy downpours.
Climate change means that extreme downpours will probably occur more frequently in the future and that we will experience more flooding.
Consequences of excessive water
- Flooding of streets and tunnels - less accessibility.
- Flooding of gardens, cellars and homes - damage to property.
- Damage for agriculture.
- Dirty water from the sewers can end up on the street, in gardens and in houses leading to increased risk of disease.
What is the government doing about this?
Water boards and local authorities are taking numerous measures to prevent flooding. Examples of measures to prevent flooding in the event of lengthy rainfall are:
- Maintaining ditches so that water can be discharged more effectively.
- Improving drainage.
- Discharging water early when it is known that lengthy rainfall is on its way.
- The planting of more greenery in built-up areas and permeable strips along roads. These allow the water to seep down into the ground instead of ending up in the sewer.
- Encouraging more greenery in gardens.
Examples of measures to combat nuisance caused by downpours are:
- Maintaining and improving sewers.
- Creating (routes to) lower areas in the built environment where rain water can be stored temporarily (such as water squares, higher kerbs and low-lying green areas).
- Discharging water early when it is known that a rainstorm is on its way.
More examples of projects can be found on the Our Water website.
Water level ordinance
Water levels are laid down in the water level ordinance of the water board (for regional waters) or Rijkswaterstaat (for the national waters). When it draws up a water level ordinance the water board assesses what the area is used for, for example agriculture, nature or buildings and the other local interests. These designated uses impose various requirements on the water level. Although, in the event of a low water level, the soil can absorb more rainwater, there is also a risk of agricultural areas and nature reserves drying out and of foundation-related problems for houses. A high water level makes it more difficult to work agricultural land.
In the event of extreme downpours the sewer often cannot cope with the amount of water. It helps if the water can then be contained elsewhere temporarily, for example in your own garden. You can install a water butt in your garden or plant more greenery. Make sure that your garden is not entirely paved and that the rain can sink down into the soil. A green garden also has a greater cooling effect in hot summers.
More tips about preventing flooding can be found at Our Water and via the links under 'read more about flooding' at the bottom of this page.