Methods for updating the drainage class map in Flanders, Belgium

Phreatic groundwater dynamics are one of the most important land characteristics for agriculture, nature development and other land uses. In Belgium, these dynamics are usually estimated from the natural drainage classes, indicated on the Belgian soil map. This information is however partly outdated, due to human intervention (artificial drainage, levelling, groundwater extraction) and –possibly- climate change. Moreover, these morphological classes were not based on actual groundwater measurements. Two groups of methods to update the old map using measured groundwater levels were applied at two locations in Flanders. A first group are 'relabeling' methods. These methods preserve the spatial structure of the old map, but assign new classes to it based on the new groundwater level observations. A second method 'remapping' uses areawide high-resolution digital auxiliary information to remap the area and create new mapping boundaries. These methods were applied to two different locations in Flanders: the valley of river Dijle (800 ha, south of Leuven) and an area close to the village of Kluizen (300 ha, east of Ghent). Validation shows that remapping provides better results than relabeling methods, although both groups of methods improve the quality of the original map