3. FUNDAMENTAL ENTITIES

3.1 The GROUNDWATER_FEATURE entity

A groundwater_feature is (or has been in the past) capable of producing data about hydrogeological conditions. Basic observations and measurements of a groundwater system can be taken from both natural and constructed features. Natural surface features such as springs and salt lakes are locations where the shallow watertable is exposed at the ground surface, enabling groundwater to be directly accessed. These groundwater outcrops may be slightly (or grossly) modified by man to increase this access. Natural underground features below the watertable, such as caves, may also be accessible. Structures such as bores, drains and trenches are specifically built to interact with the groundwater system for a variety of reasons (such as water supply, monitoring and dewatering). Other man made structures such as mine shafts, quarries, road tunnels and stopes may have been constructed for a different purpose, but act as defacto groundwater access points. Groundwater_features can be located on or under the land surface.

Groundwater_features can be categorised into types, based on their origin, surface expression and orientation (refer Figure 3.1a,b,c). Vertical, small diameter bores are very common features that allow access to groundwater. Bores are typically constructed using a drill rig, but other techniques such as driving or jetting may be used. Larger diameter vertical wells (eg. > 0.3m) tend to be manually or mechanically excavated. Bores are represented as points on a map, while the mapped expression of a well is scale dependent and may be represented as a point or a polygon. An inclined bore is orientated at an angle to the horizontal and is commonly used in mineral and petroleum exploration. Similarly oriented features with a large cross sectional area are termed inclines and are a feature of the mining industry. Constructed near-horizontal linear features that can access groundwater include surface depressions (trenches), small diameter underground conduits (drains) and larger underground passages (tunnels). The surface expression of drains and tunnels tend to be limited to access or maintenance points.

The geometry of groundwater_features can be complex. Surface workings that expose the watertable (excavations) such as quarries and pits may be represented as complicated polygons in plan view. Multiple holes and radial collectors can have vertical, inclined and horizontal components. Stopes are large underground excavations with an irregular geometry but no surface expression. Mines can consist of a complicated array of shafts, stopes and drives.

Natural groundwater_features also show variations in geometry. The term spring is confined to emergence of groundwater at a point on the land surface, while spring line is used to describe linear emergence, commonly caused by faulting or stratigraphic boundaries. A seepage is a diffuse outcrop of groundwater over a relatively large area, perhaps evident in a swamp or bog. Surface water bodies that receive groundwater are termed effluent lakes, while drainage lines that similarly receive groundwater are termed effluent streams. Access may be possible to natural underground cavities or caves that have variable geometry but limited surface expression.

Table 3.1 outlines the attributes of the groundwater_feature entity. Each groundwater_feature is uniquely defined across Australia by its feature_identifier. Hence, this is the primary key for the entity and is typically the identifier registered by the State or Territory groundwater agency prefixed by a single character identifying the State (refer Convention 4.1). A local name (eg. Canegrass No 1 Bore) can also be used to identify the feature.

Table 3.1 Attributes of the groundwater_feature entity

The owner is the person or company who has property ownership for the groundwater_feature. This is most commonly the owner of the land in which the groundwater_feature is within. The recommended format for an individual’s name is: last name, first name middle name (refer Convention 4.9). Only the most current owner of the feature is recorded, accompanied by the time that ownership was noted (owner_date). The owner_date, like all dates, may only be approximately known so the owner_date_reliability indicates how the date should be treated (refer Convention 4.5). The owner_type categorises the owner into classes such as private individual, private company or government agency.

The locator defines who chose the original location of the man made groundwater_feature, in terms of categories such as geologist, driller or owner. The total_length is the maximum dimension of the groundwater_feature. This is the maximum meterage relative to the ground surface for vertical or inclined holes, and the cumulative length of horizontal features such as drains and trenches. This may be greater than the final constructed length, as in the case when a hole is backfilled and a screen placed at a relatively shallow level.

The host_identifier and precursor_identifier define the self-referencing links for the groundwater_feature entity (refer Figure 2.1). A groundwater_feature may be part of a much larger groundwater_feature. This is the case where a piezometer has been drilled into the bed of a discharge lake, or when a stope is part of a large underground mine. The host_identifier allows the linkage to the larger groundwater_feature to be defined. The precursor_ identifier can also be used to provide linkages in time eg. it can identify the groundwater_feature that was abandoned and replaced by the new feature.

Figure 3.1a Types of groundwater_features

Figure 3.1b Types of groundwater_features

Figure 3.1c Types of groundwater_features