Groundwater Body

A homogeneous section of an aquifer, lake or coastal zone. Groundwater bodies are a basic way of dividing up aquatic environments and are intended to be the WFD evaluation unit. A body of surface water is a distinct and significant section of surface water, such as a lake, reservoir, river or a canal, or a length of a river or a canal, transitional waters or a section of coastal waters. For waterways, bodies of water are mainly delimited using the size of the waterway and the concept of a hydro-ecoregion.

A groundwater body is a distinct volume of groundwater inside one or more aquifers. Bodies of water are grouped into homogeneous types, providing a basis for defining the concept of “good status”. Bodies of water are delimited using geological and hydrogeological criteria, with a body of water generally corresponding to part or all of the hydrogeological entities defined by the BD RHF reference system (see hydrogeological entity).

The boundaries of bodies of water are stable and long lasting (impermeable geological boundaries, stable piezometric watersheds.) A topology, based on the geological characteristics and the hydrodynamic behaviour of aquifer systems, is used to delimit them.

Any abstraction points providing over 10 m3/ day of drinking water or used to supply drinking water to over fifty people must be included in a body of water, with this principle meaning that practically all formations are incorporated. Deep groundwater, with no connections to surface waterways and ecosystems, from which no abstraction occurs and which is not likely to be used for drinking water due to its quality or due to technical-economic reasons, cannot constitute bodies of water.

Depending on its size, a body of water may to some extent be spatially heterogeneous, both in terms of its hydrogeological features and its qualitative and quantitative status.

Several bodies of water may be stacked on top of each other.

The topology of bodies of groundwater is based on the intrinsic (particularly the extent and type of hydraulic conductivity) and functional (type and speed of runoff etc.) characteristics of hydrogeological systems, and comprises two levels of characteristics:

A first level with two main characteristics enabling the water body to be allocated to one of the topology’s six classes and to delimit it:

• Types of water body, six types of water body have been identified: alluvial, bedrock, volcanic structure, non-alluvial predominantly sedimentary, composite hydraulic extremely folded mountain system, and a locally impermeable aquifer system: impermeable formations incorporating smaller unconnected aquifer units
• The type of runoff (unconfined / confined).

These characteristics are useful when calculating a water body’s intrinsic vulnerability to pollution.

There is also a second level of secondary characteristics which can be applied to a water body or part of a water body, and supplement each other. These characteristics may be shared by different types of water bodies. They should not lead to the water body being re-delimited. The selected secondary characteristics are:

• Karstification

• The presence of a coastal fringe (linked to the risk of saline intrusion).

• The characteristic of “grouped unconnected aquifers” which enables unconnected (either horizontally or vertically) entities, which belong to the same type of water bodies and are subject to the same sorts of pressures, to be grouped together.

A methodological guide describes in detail the method for delimiting groundwater bodies for each type that has been defined. The guide also provides examples.