Groundwater bodies

In order to manage the groundwater, the Flemish subsurface is divided into several three-dimensional units: groundwater bodies. Within these groundwater bodies, environmental objectives are assessed and, if necessary, measures imposed. The delimitation of groundwater bodies is required by the European Water Framework Directive 2000/60/EC, which defines a body of groundwater as "a distinct body of water in one or more aquifers". The classification of the subsoil into different groundwater bodies is mainly based on the physical characteristics of the groundwater reservoirs and on the regional groundwater flow. The succession of aquifers (sand, gravel, chalk, solid rock, ...) and regionally occurring non-aquifers (clay, ...) and the prevention of clear barriers to groundwater flow (thick clay layers, fractures, groundwater separations, strongly draining rivers, salinisation limits, ...) are the most important starting points. The demarcation of the groundwater bodies was therefore based on the Hydrogeological Coding of the Subsurface of Flanders (HCOV coding) and on the classification of the subsurface of Flanders in groundwater systems. The groundwater bodies are three-dimensional and can occur both side by side and above each other. In total, there are 42 groundwater bodies. They are very different from each other: * area from 50 km2 to 6000 km2 * thickness from 20m to 1000m * Kh from 0.000005 to 2300 m/day * from sweet to salt * composed mainly of limestone, sand, gravel, peat, silt, ... * ... Groundwater bodies have both a name and a code. The code is structured as follows: The naming of a groundwater body is always based on the HCOV code of the main aquifer. Each groundwater body has also been given a meaningful code "GWS_HCOV_GWL_NR". The code consists of an abbreviation of the groundwater system in which the groundwater body is located (e.g. CVS, Central Flemish System), followed by the HCOV code, which corresponds to a main aquifer (e.g. 0600 stands for the Ledo-Paniselian-Brusselian Aquifer system). Then the abbreviation "GWL" is added, after which a serial number NR indicates the further spatial division of the aquifer into different regions. Finally, in some cases the letters "s" and "m" were added, indicating that a groundwater body was divided into a part that can be situated in the Scheldt district on the one hand or in the Meuse district on the other. To help clarify the three-dimensional aspect of groundwater bodies, horizons were added, i.e. the order in which groundwater bodies occur in the depth. This dataset contains a comma-separated list of horizons in which the groundwater body occurs. E.g. "1" means that the groundwater body is only the first (least deep) groundwater body; "1,2,3" means that, depending on the location in Flanders, the groundwater body is the first, second or third groundwater body in the depth; "3,4,5" means that the groundwater body has a minimum of two and a maximum of four groundwater bodies above it. In order to know the exact order of groundwater bodies for a given place, the layer ‘groundwater bodies (horizonts)’ can be used.