Elementary polygons of groundwater bodies — Mayotte — Report 2016

A body of groundwater is a distinct volume of groundwater within one or more aquifers, constituting the elementary separation of aquatic environments to be the WFD assessment unit. It makes it possible to define environmental objectives, to assess the state of the media and subsequently to verify the achievement of those objectives. Groundwater bodies were reported to the European Commission in 2016 on the implementation of the WFD. The layers are distributed in a format consistent with the picker data dictionary of the Water Benchmark Ref. version 1.3. The breakdown chosen for water bodies follows the following main principles: Water bodies are delimited on the basis of geological and hydrogeological criteria; Recutting of water bodies to take account of the effects of anthropogenic pressures should remain limited. Water body boundaries must be stable and sustainable Like surface water bodies, the delimitation of groundwater bodies is organised on the basis of a typology. This typology is largely based on that developed for hydrogeological entities defined in the context of the revision of the HF DB. It is based on the geological nature and hydrodynamic behaviour or large operation of aquifer systems (nature, flow rate). It comprises two levels of main and secondary characteristics. Water bodies may have exchanges between them. All water supply catchments, supplying more than 10 m³/day of drinking water or used for water supply for more than 50 people, must be included in a water body. Deep groundwater, unrelated to water courses and surface ecosystems, in which no abstraction takes place and which is not likely to be used for drinking water because of its quality (salinity, temperature, etc.), or for technical and economic reasons (disproportionate cost of abstraction) may not constitute bodies of water. Given its size, a body of water may have a degree of spatial heterogeneity in terms of both its hydrogeological characteristics and its qualitative and quantitative state. At any point more than one water body may overlap. The PolygMasseDEauSouűine layer is the result of the single-file agglomeration of all groundwater bodies divided into elementary multipolygons corresponding to each of their depth level. The entire national territory is covered, the polygons overlap. In other words, if one seeks to identify the water bodies present at a point in the territory, this layer will be able to make 1 to 10 water bodies differentiated only in the order of the associated overlay. In line with the data dictionary V1.3, the layer consists of the same attributes as the MasseDEauSouine layer with: — The addition of the ‘Level’ field: Depth level of the elemental multipolygon of the groundwater body; — The addition of the “CdPolygMasseDEauSou-ine” field: Unique code for the elemental multipolygon of the groundwater body.