Major floods are not only caused by dike breaches, as demonstrated in July 2021 when the province of Limburg was hit by heavy rainfall resulting in enormous damage. What would happen if such extreme rainfall occurred in other parts of the Netherlands? This was investigated for thirteen Dutch regions commissioned by the Ministry of Infrastructure and Water Management.
These water images show what happens when 200 mm of rain falls within 48 hours, comparable to the amount of rain that caused the floods in Limburg. For reference: on average, 875 mm of rain falls in the Netherlands in a year. The chance of this event occurring is therefore very small, but no longer unimaginable, making it important to be well prepared. By knowing where the biggest problems may arise, we can determine where measures need to be taken.
Impact on the Province of Utrecht
The province of Utrecht has various types of landscapes. In the lower-lying areas and polders, during an extreme shower, water will often reach knee height (about 60 cm) and remain for one to three weeks. This is because the area is very flat and the water system cannot discharge such large amounts of water. Around the Utrechtse Heuvelrug, the situation is quite different due to elevation differences. Here, water can flow down quickly, resulting in large amounts of water at the bottom of the hill. The flow speed can also cause dangerous situations.
Long-lasting water nuisance can also occur in cities and villages. This affects accessibility and can also cause damage to buildings. The biggest challenge lies in places where important facilities are located, such as electrical cabinets, telephone connections, and main roads. Accessibility to hospitals and other critical emergency services/facilities is also a concern.
No street-level detail
The maps in the stress test do not show street-level details; they only provide a general view of how water behaves during a large-scale rainfall event. There may be more urban areas vulnerable than the maps indicate, as effects can be greater in reality when sewer problems are also taken into account. The water images can be viewed via the national Climate Effect Atlas external link.
Visualizing the consequences
The next step is to develop an impact assessment. For this, the province will consult with safety regions and water boards to map out the possible consequences of failure of vital and vulnerable functions, such as hospitals and dikes. Then it will be discussed which consequences are acceptable and where measures are needed. These discussions will take place from the end of 2025. By the end of 2026, the results of the impact assessments will be shared in the National Approach to Water Nuisance.
Being prepared for climate change
Due to climate change, we face more frequent heavy rainfall. The water system, including pumps and sluices, cannot discharge such large amounts quickly enough. By creating more space for water, potential water nuisance can be reduced.
Three regions within the province of Utrecht
The studies are divided into thirteen different regions, based on catchment areas. The province of Utrecht falls within three regions: Amsterdam-Rhine Canal-North Sea Canal area, Valley and Veluwe, and Rivierenland. Different models may have been used per region, meaning the effects are displayed differently on the map. This is the case, for example, with the Utrechtse Heuvelrug. In practice, similar water nuisance will occur on the west and east sides of the Utrechtse Heuvelrug.
For press information:
jiri.glaap@provincie-utrecht.nl
06 39 63 21 97
