Incidence area of the HCOV main units

Flanders is composed of an alternation of aquifers (sand, gravel, chalk, rock, etc.) and regionally occurring non-aquifers (e.g. clay). The sequence of these aquifers and aquitards has its own coding in Flanders: hydrogeological Coding of the Subsoil of Flanders (HCOV coding). The HCOV coding is composed of main hydrogeological units, sub-units and basic units. The main unit brings together a sequence of geological layers which have broadly the same hydrogeological characteristics and thus form a whole.佛兰德斯地区由含水层（aquifer）与区域分布的非含水层（non-aquifer）交替组成，含水层涵盖砂、砾石、白垩、岩石等，非含水层例如黏土。该区域内的含水层与弱透水层（aquitards）序列设有专属编码体系：佛兰德斯地下水文地质编码（HCOV编码）。HCOV编码由主要水文地质单元、次级单元与基本单元构成。其中，主要水文地质单元指具备大致相同水文地质特征、可作为统一整体的一套地质层序。