What does the flood hazard map of Wallonia say?

The flood hazard map (cartographie de l’aléa d’inondation), approved by the Walloon Government on 4 March 2021, shows where water can reach, with a hazard from very low to high. In a hazard zone the municipality can refuse a permit or attach conditions (CoDT art. D.IV.57, 3°). A high-hazard zone also matters for insurance: for a building newly built there after the zone was delimited, an insurer may refuse natural disaster cover.

Two kinds of water

The map distinguishes a watercourse overflowing its banks (débordement, shown as zones) from rainwater running off over the ground (ruissellement, shown as lines). It does not show sewer backflow, rising groundwater or water in karst. The map of the areas flooded in July 2021 is not a reference: only the approved map counts.

Other things often matter on the same plot too, such as the BDES and its extract and crime figures by municipality. You can see how a report brings them together in the sample report.

Four classes

Very low (très faible) and low (faible): water can reach there, but rarely or shallowly.
Medium (moyen): an intermediate class; a building project may need a note on its effects on water.
High (élevé): among other things a flood that can occur at least every 25 years, with at least 30 cm of water.

Building in a hazard zone

After the floods of July 2021 a circular of 23 December 2021 asks not to build up land in a high-hazard zone any more unless a hydraulic study shows it can be done, and a technical note for a medium hazard. It is a guideline, not a ban: the municipality decides application by application.

In a high-hazard zone most exemptions from a permit also fall away: a veranda, a garden shed, a carport, a swimming pool or a fence needs a permit there (CoDT art. R.IV.1-1).

Insurance

The insurance act allows an insurer to refuse natural disaster cover for a building in a risk zone that was built more than eighteen months after that zone was published. In Wallonia the risk zones are the high flood hazard zones. For an existing house built before that, the right to refuse does not apply; do ask your insurer what the premium is for this address.

At the sale

The planning information states whether the property is exposed to a natural risk such as flooding (CoDT art. D.IV.97, 9°), and the notary includes it in the preliminary contract and the deed.

What the Perceelscan shows

Section 11 of the report shows the highest flood hazard on the plot, with its type (a watercourse overflowing or surface run-off), and section 09 says which exemptions a high hazard removes there.

Where to check it yourself

On WalOnMap, with the flood hazard layer. Legally only the paper map at 1:10,000 signed by the minister counts; if in doubt, ask the municipality.

Can I build in a high flood hazard zone in Wallonia?

Not automatically. The municipality can refuse the permit or impose conditions, such as a higher floor level, and the circular of December 2021 asks for a hydraulic study showing that it can be done. Small works that are exempt elsewhere need a permit there.

Am I insured in a Walloon flood zone?

An existing house remains insurable against natural disasters. The insurer may refuse only for a building put up in a high-hazard zone more than eighteen months after that zone was published.

In the other regions

In Flanders: What do the P-score and the G-score mean?
In Flanders: What is the water test (watertoets)?
In Brussels: How do you check the flood risk in Brussels?

Sources

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Updated on 26 October 2026