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Likewise, management areas are also relational entities in the sense that they are typically necessarily linked with a unit or system and possibly a fluid body. Management areas
are earth bodies identified for groundwater management purposes and their boundaries can be delineated by social factors, such as policy or regulation, in addition to physical
factors related to hydrogeology or hydrology.
7.2 Fluid Bodies
These are distinct bodies of fluid liquid or gas that fill the voids in hydrogeological units. Fluid bodies are made of biologic e.g. organisms, chemical e.g. solutes, or
material constituents e.g. sediment. While it is expected that the major constituent of a fluid body will be water, the conceptual model allows for other types of major
constituents such as petroleum. Minor constituents are not necessarily fluids, but can be gases, liquids, or solids, and are included in the fluid body in various forms of mixture,
such as solution, suspension, emulsion, and precipitates. Fluid bodies can also have other fluid bodies as parts, such as plumes or gas bubbles. Surfaces can be identified on a fluid
body, such as a water table, piezometric or potentiometric surface, and some such surfaces can contain divides, which are lines projected to the fluid surface denoting
divergence in the direction of flow systems.
7.3 Voids
Voids are the spaces inside a unit e.g. aquifer or its material e.g. the sandstone material of an aquifer, and might contain fluid bodies. Voids are differentiated from porosity, in
that porosity is a ratio of void volume to total volume of unit plus voids, while voids are the spaces themselves. It is important to conceptually differentiate voids from units and
their containers, in order to represent, for example, the volume of fractures, caves, or pores in a particular unit or portion thereof.
7.4 Flow
Groundwater flow denotes the process by which a fluid enters or exits a container unit or its voids, or flows within them. Flow between one container or void and another is
named InterFlow, and flow within a container or void is named IntraFlow. Recharge is the flow into a groundwater container or void, and discharge is flow out of a groundwater
container or void. The reciprocal source or destination entity can be any appropriate container or void such as a river, lake, pipe, dam, canyon, flood plain, etc. A flow system
is then a collection of flows ordered in a sequence from recharge to discharge, such that the flow segments of the system make up a connected flow path from source to
destination. A water budget is a measure of the balance of recharge and discharge valid for a specific time and relative to a specific groundwater feature, such as a basin, aquifer,
management area, or well.
7.5 Wells
