Flood zone (záplavové území)

Under Section 66 of the Czech Water Act, a flood zone is an administratively designated area that may be inundated during a natural flood. The water authority designates it by a measure of general nature (opatření obecné povahy) at the proposal of the river manager - the regional authority for significant rivers, otherwise the municipal office of a municipality with extended powers. Under Decree No. 79/2018 Coll. its boundary is the flood line of the flood with a 100-year return period, i.e. the 100-year flood.

What a flood zone map shows

The flood zone proposal includes flood hazard maps for floods with return periods of 5, 20, 100 and 500 years: the extent of flooding, water depths and velocities. A Czech flood map therefore usually shows several layers, from the most frequent 5-year flood to the extreme 500-year flood. In the built-up area, in areas zoned for development and elsewhere as needed, the authority also defines an active zone where water flows most dangerously.

What it means for a buyer

• In the active zone the Water Act bans new buildings, fences and storing material that can be washed away, with few exceptions (Section 67).
• For the rest of the flood zone the water authority sets restrictive conditions by a measure of general nature.
• Owners of flood-threatened buildings in a flood zone prepare their own flood plan (Section 71(4)).
• The boundary often runs right next to houses, so compare it with the outline of the building, not just the address point.

Frequently asked questions

If the map shows nothing, is the place safe?

Not necessarily. Not every stream has a designated flood zone. Where it is missing, authorities may rely on data from river basin and river managers (Section 66(5) of the Water Act). River flood maps also do not cover flash floods running off slopes and fields. The municipal flood plan and the experience of neighbours help.

Where can the flood zone be found?

Designated zones and their active zones are shown in the HEIS map of the T. G. Masaryk Water Research Institute (VÚV TGM); the authority that designated the zone also holds the documentation. Water depths and velocities for selected river sections are in the flood hazard maps of the Ministry of the Environment. The decision on the flood zone is also sent to those who prepare the spatial analytical data for planning.