Hydrogeological entities - Metropolis

The hydrogeological entity is a part of the geological space, aquifer or non-aquifer, corresponding to a physical system characterised in terms of its state and hydrogeological characteristics.

The hydrogeological entity must be understood in a systemic sense and corresponds to a division of the geological space carried out at a given stage of knowledge, in particular for deep systems.

The constitution of hydrogeological entities comes from the knowledge at a given date of the underground environment (geological map, geological section, geological log, structural scheme and piezometric map).

Hydrogeological entities can be multipart.

Hydrogeological entities cover the entire territory ensuring a horizontal and vertical relationship of entities in accordance with the principle of completeness.

A hydrogeological entity is a part of the geological space:
- delimited to a certain scale (level of use)
- related to a type of geological formation (theme)
- defined by its aquifer potentials (nature)
- characterized by a type of porosity (middle)
- characterized by the presence or not of a tablecloth, which can be free, captive or free and captive (state)

They have been defined according to rules developed within the framework of a common national methodology and validated by a national steering committee under the responsibility of the ministry in charge of the environment.

A hydrogeological entity will be represented by its orthogonal projection to the ground. The reference scale is 1/50 000th, i.e. the scale of the national geological repository.

Each entity has a code that is assigned by the BRGM (Order of 26 July 2010, SNDE).

(According to Sandre, dictionary of the SAQ V 2.2 hydrogeological repository)