Cluster showers and flooding 

Nuisance caused by flooding

When ditches, streams, or canals overflow their banks, or when a dyke breaches, flooding causes disruption. Fortunately, this happens very rarely. When it does happen, the water authority takes action to resolve the problems.

Disruption after heavy rain

During a downpour, a large amount of rain falls in a small area in a short period of time. All that water cannot always be drained away immediately and remains on the streets or land. Basements can get wet and, in the worst case, water can enter the house. This is because cities often have a lot of hard, stony surfaces: pavements, streets, buildings, and parking spaces. These surfaces do not allow rainwater to pass through. Agriculture also suffers greatly from overly wet soil. 

When it rains really hard, a lot of water flows from roofs and roads into the municipal sewer system. Sometimes the sewer system cannot cope with this. Water then flows from the sewer into a ditch, stream, or canal, or onto the street. We call this a sewer overflow.

Groundwater flooding

When do we talk of flooding?

When you get an average of 10 litres of water per square metre within 24 hours, the municipal sewer system must be able to handle it. Flooding of up to 15 cm once every two years is still reasonable. Adjacent buildings should remain dry, as the floor level is normally 5 cm higher.

Up to six times a year, overflow of excess sewage may occur in a separate sewer system. In such a system, dirty water from households is discharged separately from clean rainwater. Because overflow can affect the quality of surface water, large cellars are sometimes constructed to collect sewage termporarily. The dirty water can then be discharged through the sewer system. This prevents it from ending up in surface water.

Why are heavy downpours a problem for the sewer system?

During heavy downpours, a large amount of precipitation falls in a short period of time. The sewer system cannot handle that much water at once. This can cause drains to overflow and streets to flood temporarily. It can also lead to sewer overflows.

How does rainwater cause flooding?

Due to overflow in a combined sewer system

During heavy rainfall, the capacity of the sewer system is not always sufficient, and the sewer system can no longer cope with the amount of rainwater. Even manhole covers can be lifted by water pressure from the sewer. This results in overflow. The excess rainwater (mixed with wastewater) then flows directly from the sewer into surface water. Or it ends up on the street. This can lead to traffic disruption, especially in urban areas.

Due to flooding

Flooding can also occur when ditches and ponds fill up and overflow their banks . Or when rainwater remains on the streets (which is better than the water flowing into homes).

What do we do in the event of flooding?

When there so much rain that flooding occurs, we will take action to deal with it. How we do this is set out in our emergency plan. This also specifies who we consult and how we inform our community and the media. More information:

• Emergency