Hydrogeological entities — Métropole

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

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

The constitution of hydrogeological entities is derived from knowledge at a given date of the underground environment (geological map, geological cutting, geological log, structural diagram and piezometric map).

Hydrogeological entities can be multi-part.

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 on a certain scale (level of use)
— attached to a type of geological formation (theme)
— defined by its aquifer potentialities (nature)
— characterised by a type of porosity (mid)
— characterised by the presence or not of a tablecloth, which may be free, captive or free and captive (state)

They have been defined in accordance with rules developed within the framework of a common national methodology and validated by a national steering committee under the responsibility of the Ministry responsible for the environment.

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

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

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