Occurrence areas of the HCOV main units

Flanders is made up of an alternation of aquifers (sand, gravel, chalk, solid rock, ...) and regionally occurring non-aquifers (e.g. clay). The sequence of these aquifers and aquitards has its own coding in Flanders: the Hydrogeological Coding of the Subsurface of Flanders (HCOV-coding). The HCOV coding is made up of hydrogeological main, sub and base units. The main unit groups a sequence of geological layers that have broadly the same hydrogeological properties and thus form a single whole.