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Surface water flooding

Pluvial flooding is flooding caused by too much surface water. This type of flooding generally occurs in low-lying areas ("basins"), or in areas where water levels are already high after intense, heavy rainfall.  

 

Surface water flooding occurs when the amount of rainfall exceeds the capacity of the soil or drainage system to absorb the water (for example, because dry soil prevents infiltration, or because the drainage system is saturated).  

 
There are two distinct phenomena: 

  1. Surface water flooding. The drainage system has insufficient capacity, and water accumulates on the surface. This is a slow process, which allows people to get to safety.  
  2. Flash floods. After heavy rains, water levels rise rapidly. There is a significant difference in the level between the valley floor and more elevated ground. Flash floods are dangerous, as they carry debris and have very strong currents. 

 

Causes

/

Consequences

What can you do?  

BEFORE 

  • Find out where flood-prone areas are. 
  • Protect your home against water damage. Read the brochure of the WPS Environment. 
  • Keep gutters and ditches clean and unclogged. 
  • Envisage waterproof materials for cellar hatches, inspection chambers, etc. 
  • Envisage materials for raising the living areas on the ground floor and basement, such as bricks or sandbags. 
  • Envisage boots, buckets and squeegees. 
  • Protect your important documents and valuables from the water, for example by storing them at height. 
  • Make sure you know where the gas and electricity can be switched off.    

DURING

  • Do you need help from the fire service? 
    • Call for help via the digital counter 1722.be or the electronic form of your local fire service. 
    • Call 1722 if this number is active. 
    • Keep the number 112 available for people in danger. 
  • Is someone potentially in mortal danger? Always call 112. 
  • Limit your movements and avoid dangerous areas. 
  • Use sandbags to block the doorways to basements, exterior doors, etc. 
  • Remove carpets and place furniture and valuables at a safe height. 
  • Switch off gas, electricity and water if necessary. 
  • Park your car in a safe place. Do not leave it in your garage. 
  • Make sure that unsecured objects in the garden cannot be carried or washed away. 

Do you have to evacuate? 

AFTER 

  • Clean your home and disinfect damaged areas. 
  • Ventilate rooms adequately, but also heat them so that humidity evaporates. 
  • Follow the recommendations of the authorities regarding the use of tap water.  
  • Have you suffered any damage? 
  • Do you need help from the fire service? 
    • Call for help via the digital counter 1722.be or the electronic form of your local fire service. 
    • Call 1722 if this number is active. 
    • Keep the number 112 available for people in danger. 
  • Do you not need help from the fire service? Call in a qualified professional or carry out the repairs yourself (e.g. a tree that has fallen in the garden, a damaged garden shed, hail damage to your car). 
  • Take photos of the damage: these may prove useful for your insurance claim. 
  • Contact your insurance provider as soon as possible. They will answer all your questions and help you start the claims process. 
  • Check whether the Disaster Fund will intervene in your case. 

Read more advice from the WPS Environment. 

Impact and probability 

The figures relating to probability and impact describe considerable pluvial floods. The BNRA theoretically describes such a scenario as follows: 

  • Just one village is seriously affected, in a sparsely populated local area.  
  • The water flow velocity is relatively low (< 1 m/s). The amount of debris carried by the water is limited, so people are not carried away.   
  • The maximum flood depth is less than 0.3 m. This is the maximum height reached by the water above the ground. 

How should you interpret these results?

Within the BNRA, experts assessed three scenarios for each risk: considerable, major or extreme. On each page, you will find the results of the scenario with the highest score based on the combination of likelihood and impact. This does not mean that this scenario will occur or is the most likely. Read more here about how to correctly interpret the results. 
 

Probability

Strong

Human impact

Very weak

Societal impact

Very weak

Environmental impact

No impact

Financial impact

Very weak

What do the authorities do? 

The regional authorities take various preventive measures to avoid flood damage, such as imposing building regulations or planning flood zones or additional infrastructure (sluices, pumping stations, etc.). 

The regional authorities also continually monitor the water situation, in collaboration with the RMI. Based on observations, weather forecasts and thresholds, they attempt to predict the risk of flooding. When these thresholds are exceeded, they inform the local, provincial and national authorities. 

If rising waters cause flooding, the local and provincial authorities launch their special emergency and intervention plans for floods. 

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