3.2 The SITE entity
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The site of a groundwater_feature is
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The purpose of the site is to represent a groundwater_feature as a point on a map.
Groundwater_features such as springs are by definition, point-like on the land surface, so the site entity can be used to adequately represent the surface geometry of these features. For bores (which are also point-like features in plan view), the site corresponds to the bore collar. For linear features such as drains or trenches, the site is the discharge point of the feature. For polygonal groundwater_features such as seepage areas, the site is the centroid of the polygon.
Bores and wells can be graphically represented by a vertical line (termed the reference line) passing through the site location. By using the geographical coordinates for the site and reference elevations (refer datum_plane entity), information associated with the bore or well (eg. stratigraphic log, water cuts, casing details) can be positioned down the hole. This can also be achieved for inclined holes and inclines when the azimuth and dip attributes are known (refer Figure 3.2).
Table 3.2 Attributes of the site entity
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Name |
Data Type |
Description |
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feature_ identifier |
character |
unique identifier for the groundwater_feature at the site |
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latitude |
number |
site latitude in GDA94 decimal degrees with negative values for southern hemisphere (Australia) |
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longitude |
number |
site longitude in GDA94 decimal degrees with positive values for eastern hemisphere (Australia) |
|
code |
method used to derive geographical coordinates of site |
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|
error |
number |
nominal error radius of site location in horizontal plane, metres |
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bibliographic_source |
character |
bibliographic reference if location derived from a map, report, air photo or image |
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scale |
number |
scale used in source map, report, air photo or image (1:n) |
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person |
character |
person responsible for determining coordinates of site |
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organisation |
character |
organisation who determined coordinates of site |
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siting_date |
date |
date/time that site coordinates were determined |
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code |
reliability of date/time that site coordinates were determined |
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azimuth |
number |
bearing in decimal degrees of reference line in the horizontal plane clockwise from the north |
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dip |
number |
angle in decimal degrees at which reference line is inclined from the horizontal, a positive dip angle is measured downward from the horizontal plane |
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directions |
character |
description of route used to travel to site, typically including road names and prominent landmarks |
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comments |
character |
comments about site of groundwater_feature |
A groundwater_feature can have only one site. Hence, the feature_identifier is the primary key for the site entity. The located point on the land surface for the groundwater_feature is defined by a latitude and longitude using the Geocentric Datum of Australia (GDA94) as the standard geographical coordinate system (refer Convention 4.3). The method defines how these coordinates were obtained with the associated level of accuracy recorded in error. The error defines the radius of a horizontal circle with its origin defined by the site longitude and latitude that would effectively encompass the actual location of the groundwater_feature. It is possible for many groundwater_features to be co-located, in the sense that they are all within the same circular area defined by the same latitude, longitude and error attributes.
Other attributes such as bibliographic_source, scale, person, organisation and siting_date define further how and when the site for the groundwater_feature was established. The Author-Date system (also called the Harvard system) is used to format the reference details stored in bibliographic_source. Refer to Convention 4.6 for guidelines on this method of citation. The recommended format for the person name is: last name, first name middle name (refer Convention 4.9).
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