Atlas of Flood Maps

EU Flood Risk Maps Q4310 September, 2007
Examples from EU countries
WL | Delft Hydraulics
4.2 Belgium
4.2.1 Flanders
For the Province of Flanders in Belgium, three types of flood plain maps are developed:
� The NOG-maps (Naturally flooded area map) contain the areas that are known as being
flooded through soil-mapping. These maps show the river sediments (alluvium) and
slope (gravity-caused) sediments (colluvium) zones in the soilmap that has been
constructed on a scale 1:20.000
� The ROG-maps (Recently flooded area map) show the recently flooded areas in the
period 1988-2006 based upon manual cartography, local terrain knowledge,
photographs, (areal) movies, water authorities, Provinces, municipalities, consultants
and others on topographical maps with scale 1:10.000. An automatic correction of the
ROG-map has been performed using the DTM-Flanders (5*5 m) and GIS-techniques.
This side-product is called the ROG-DHM map
� The MOG-maps (Modelled flooded area maps) shows the flooded areas for about 2000
km of rivers that have been modelled hydrological and hydrodynamical. The maps show
flood extent, flood depth, flood time, flood frequency (2, 5, 10, 15, 20, 25, 30, 40, 50,
75, 100, 150, 200, 250, 300, 500 and 1000 years). The MOG-map can be used till a
scale of 1:2500.
The flood extension maps are available from an interactive internet site 2 called the “Geoloket
Overstromingskaarten” and “Geo-loket Watertoets”; the same site is also used for
other map purposes, e.g. soil maps, colour orthophotos, satellite images, water quality, etc.
The dark blue in the “Overstromingskaarten” can be chosen for the ROG or NOG maps or
for a combination of the surveyed ROG together with the MOG with a return period of 25
years. In the “watertoets” the dark blue zones are the combination of the ROG and a MOG
with a return period of 100 years. The light blue zones are the NOG without the built-up
areas. Explanation on the interactive information, and how the flood extensions have been
calculated, are given in an accompanying digital document (“Risicozones overstroming –
Begeleidende Nota”). Examples of a map produced with this internet site are shown in
Figure 4.8 and Figure 4.9. There is a legend to the maps, but this is written in Dutch.
Comment on the maps
On the maps, colours are used to indicate areas that are floodable:
� from any water course (pink)
� from the sea (dark green)
� recently flooded (ROG – dark blue)
� floodable by excessive rainfall (brown)
� floodable by either excessive rainfall or from a water course (orange)
Especially the two last items are rare on flood maps.
2 http://geo-vlaanderen.gisvlaanderen.be/geo-vlaanderen/overstromingskaarten/
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