iv.  Submitting organizations

The following organizations submitted this Document to the Open Geospatial Consortium (OGC):

Geological Survey of Canada (GSC), Canada

U.S. Geological Survey (USGS), United States of America

Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia

Bureau of Meteorology (BOM), Australia

Federation University Australia (FedUni), Australia

Bureau de Recherches Géologiques et Minières (BRGM), France

Salzburg University (U Salzburg), Austria

 

The following organizations contributed to the initiation or development of this standard:

Geological Survey of Canada (GSC), Canada

U.S. Geological Survey (USGS), United States of America

Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia

Federation University Australia (FedUni), Australia

Bureau of Meteorology (BOM), Australia

European Commission, Directorate General – Joint Research Centre  (JRC), European Union

Polish Association for Spatial Information

Polish Geological Institute (PGI), Poland

Geological Surveys of Germany (GSG), Germany

Salzburg University (U Salzburg), Austria

Bureau de Recherches Géologiques et Minières (BRGM), France

British Geological Survey (BGS), U.K.

International Groundwater Resources Assessment Centre (IGRAC), UNESCO

v.  Submitters

All questions regarding this submission should be directed to the editor or the submitters:

1.    Scope

This document is an OGC® conceptual, logical and encoding standard for GWML2, which represents key groundwater data. GWML2 is implemented as an application schema of the Geography Markup Language (GML) version 3.2.1, and re-uses entities from other GML application schema, most notably the OGC Observations & Measurements standard and the OGC/IUGS GeoSciML 4.0  (OGC 16-008) standard. GWML2 version 2.2 (this document) updates version 2.1, which was developed by the GW2IE (OGC, 2016), by importing GeoSciML 4.0 instead of GeoSciML 3.2.0, and by using TimeseriesML (OGC 15-042r2) instead of OGC WaterML2.0 part 1 – Timeseries.

GWML2 is designed to enable a variety of data exchange scenarios. These scenarios are captured by its five motivating use cases, including:

1. a commercial use-case focused on drilling water wells with knowledge of aquifers,
2. a policy use case concerned with the management of groundwater resources,
3. an environmental use-case that considers the role of groundwater in natural eco-systems,
4. a scientific use-case concerned with modeling groundwater systems, and
5. a technologic use-case concerned with interoperability between diverse information systems and associated data formats.

GWML2 is designed in three stages, each consisting of a schema that builds on the previous stages. The three schemas include:

1. Conceptual (UML): a technology-neutral schema denoting the semantics of the domain,
2. Logical (UML): a GML-specific schema that incorporates the OGC suite of standards,
3. XML schema (XSD): a GML syntactical encoding of the logical schema.

In addition, this standard describes general and XML-specific encoding requirements, general and XML-specific conformance tests, and XML encoding examples. The standard is designed for future extension into other non-XML encoding syntaxes, which would require each such encoding to describe the related schema, requirements and conformance classes, as well as provide examples.

The GWML2 Logical and XML schemas are organized into 6 modular packages:

1. GWML2-Main: core elements such as aquifers, their pores, and fluid bodies,
2. GWML2-Constituent: the biologic, chemical, and material constituents of a fluid body,
3. GWML2-Flow: groundwater flow within and between containers,
4. GWML2-Well: water wells, springs, and monitoring sites,
5. GWML2-WellConstruction: the components used to construct a well,
6. GWML2-AquiferTest: the elements comprising an aquifer test (e.g. a pumping test).

Altogether, the schemas and packages represent a machine-readable description of the key features associated with the groundwater domain, as well as their properties and relationships. This provides a semantics and syntax for the correct machine interpretation of the data, which promotes proper use of the data in further analysis. Existing systems can use GWML2 to ‘bridge’ between existing schema or systems, allowing consistency of the data to be maintained and enabling interoperability.

2.    Conformance

This standard has been written to be compliant with the OGC Specification Model – A Standard for Modular Specification (OGC 08-131r3). Extensions of this standard shall themselves be conformant to the OGC Specification Model.

2.1    XML implementation

The XML implementation (encoding) of the conceptual and logical groundwater schemas is described using the XML Schema language and Schematron.

Requirements for one standardization target type are considered:

• data instances.

i.e. XML documents that encode groundwater data. As data producing applications should generate conformant data instances, the requirements and tests described in this standard effectively also apply to that target.

Conformance with this standard shall be checked using all the relevant tests specified in Annex A (normative) of this document. The framework, concepts, and methodology for testing, and the criteria to be achieved to claim conformance are specified in ISO 19105: Geographic information — Conformance and Testing. In order to conform to this OGCencoding standard, a standardization target shall implement the core conformance class, and choose to implement any one of the other conformance classes (i.e. extensions).

All requirements-classes and conformance-classes described in this document are owned by the standard(s) identified.

2.2    Use of vocabularies

Controlled vocabularies, also known as code-lists, are used in data exchange to identify particular concepts or terms, and sometimes relationships between them. For example, an organization may define a controlled vocabulary for all observed phenomena, such as water quality parameters, that are to be exchanged between parties. Some of these definitions may be related by hierarchical relationships, such as specialization, or through other relationships such as equivalence.

GroundWaterML2.0 does not define a set of vocabularies for groundwater data exchange in this version. It is envisaged that specific communities will develop local vocabularies for data exchange within the community. Future work within the Hydrology Domain Working Group could address standardized controlled vocabularies for the groundwater domain. Such vocabularies require a governance structure that allows changes to be made as definitions evolve, possibly using the OGC definition namespace (http://www.opengis.net/def/gwml/2.2), which is governed by the OGC Naming Authority (OGC-NA). The OGC-NA is responsible for processing requests to change or add new definitions to this namespace. The procedures for the OGC-NA are outlined in OGC document 09-046 (OGC-NA – Procedures) and the structure of URIs is outlined in OGC 09-048 (OGC-NA – Name type specification – definitions).

The following convention has been used throughout the document to identify attributes requiring controlled vocabularies:

• In the conceptual model, such attributes are typed with a name ending by “Type” (ex : PorosityType); and
• In the logical model this suffix becomes ‘TypeTerm’ (ex : PorosityTypeTerm).

2.3    Groundwater data

Groundwater data conforming to this standard are encoded in GML-conformant XML documents, for this version of GWML2. It is anticipated that future versions or extensions will develop additional encodings such as JSON or RDF.  The standard MIME-type and sub-type for GML data should be used to indicate the encoding choice as specified in MIME Media Types for GML, namely: application/gml+xml.

Conformance with this standard shall be checked using all the relevant tests specified in Annex A (normative) of this document. The framework, concepts, and methodology for testing, and the criteria to be achieved to claim conformance are specified in the OGC Compliance Testing Policies and Procedures and the OGC Compliance Testing web site[1].

In order to conform to this OGC™interface standard, a software implementation shall choose to implement:

a)     Any one of the conformance levels specified in Annex A (normative).

All requirements-classes and conformance-classes described in this document are owned by the standard(s) identified.

3.    References

The following normative documents contain provisions that, through reference in this text, constitute provisions of this document. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. For undated references, the latest edition of the normative document referred to applies.

OGC: OGC 15-043r3, Timeseries Profile of Observations and Measurements (2016)

OGC: OGC 08-131r3, The Specification Model – A Standard for Modular Specification (2009)

OGC: OGC 10-126r4, WaterML2.0 part 1 – Timeseries (2014)

OGC: OGC 15-042r2, TimeseriesML 1.0 – XML Encoding of the Timeseries Profile of Observations and Measurements (2016)

OGC: OGC 15-082, OGC GroundWaterML 2 – GW2IE Final Report (2016)

OGC: OGC 16-008, OGC Geoscience Markup Language 4.0 (GeoSciML) (in publication)

OGC: OGC 06-121r9, OGC Web Services Common Standard (2010)

ISO / TC 211: ISO 19103:2005, Conceptual Schema Language (2005)

ISO: ISO 8601:2004, Data elements and interchange formats – Information interchange – Representation of dates and times (2004)

OGC: OGC 10-004r3, OGC Abstract Specification Topic 20 – Observations and Measurements (aka ISO 19156:2011) (2011)

OGC: OGC 08-015r2, OGC Abstract Specification Topic 2 – Spatial Referencing by Coordinates (aka ISO 19111:2007) (2007)

OGC: OGC 07-011, OGC Abstract Specification Topic 6 – Schema for Coverage geometry and functions (aka ISO 19123:2005) (2005)

OGC: OGC 01-111, OGC Abstract Specification Topic 11 – Geographic information — Metadata (aka ISO 19115:2003) (2003)

OGC: OGC 07-036, Geography Markup Language (aka ISO 19136:2007) (2007)

OGC: OGC 10-004r1, Observations and Measurements v2.0 (also published as ISO/DIS 19156:2010, Geographic information — Observations and Measurements) (2010)

OGC: OGC 10-025r1, Observations and Measurements - XML Implementation v2.0 (2011)

OGC: OGC 08-094r1, SWE Common Data Model Encoding Standard v2.0 (2011)

ISO/IEC: Schematron: ISO/IEC 19757-3:2006, Information technology — Document Schema Definition Languages (DSDL) — Part 3: Rule-based validation — Schematron (2006) (see http://standards.iso.org/ittf/PubliclyAvailableStandards/c040833_ISO_IEC_19757-3_2006(E).zip)

OGC: OGC 12-000, SensorML (2014)

Schadow, G and McDonald, C.: Unified Code for Units of Measure (UCUM) – Version 1.8 (2009)

OMG: Unified Modeling Language (UML). Version 2.3 (2010)

W3C: Extensible Markup Language (XML) – Version 1.0 (Fourth Edition) (2006)

W3C: XML Schema – Version 1.0 (Second Edition) (2004)

4.    Terms and Definitions

This document uses the terms defined in Sub-clause 5.3 of [OGC 06-121r8], which is based on the ISO/IEC Directives, Part 2, Rules for the structure and drafting of International Standards. In particular, the word “shall” (not “must”) is the verb form used to indicate a requirement to be strictly followed to conform to this standard.

For the purposes of this document, the following additional terms and definitions apply.

4.1       coverage

Feature that acts as a function to return values from its range for any direct position within its spatial, temporal or spatiotemporal domain.

[ISO 19123:2005, definition 4.17]

4.2 domain feature

Feature of a type defined within a particular application domain.

NOTE: This may be contrasted with observations and sampling features, which are features of types defined for cross-domain purposes.

[ISO 19156, definition 4.4]

4.3 element <XML>

Basic information item of an XML document containing child elements, attributes and character data.

NOTE: From the XML Information Set ― each XML document contains one or more elements, the boundaries of which are either delimited by start-tags and end-tags, or, for empty elements, by an empty-element tag. Each element has a type, identified by name, sometimes called its ‘generic identifier’ (GI), and may have a set of attribute specifications. Each attribute specification has a name and a value.

[ISO 19136:2007]

4.4 feature

Abstraction of a real-world phenomena.

[ISO 19101:2002, definition 4.11]

4.5 GML application schema

Application schema written in XML Schema in accordance with the rules specified in ISO 19136:2007.

[ISO 19136:2007]

4.6 GML document

XML document with a root element that is one of the elements AbstractFeature, Dictionary or TopoComplex, specified in the GML schema or any element of a substitution group of any of these elements.

[ISO 19136:2007]

4.7 GML schema

Schema components in the XML namespace ―http://www.opengis.net/gml/3.2‖ as specified in ISO 19136:2007.

[ISO 19136:2007]

4.8 measurement

Set of operations having the objective of determining the value of a quantity.

[ISO/TS 19101-2:2008, definition 4.20]

4.9 observation

Act of observing a property.

NOTE:            The goal of an observation may be to measure or otherwise determine the value of a property.

[ISO 19156:2011 definition 4.10]

4.10 observation procedure

Method, algorithm or instrument, or system which may be used in making an observation.

[ISO19156, definition 4.11]

4.11 observation result

Estimate of the value of a property determined through a known procedure.

[ISO 19156:2011]

4.12 property <General Feature Model>

Facet or attribute of an object referenced by a name.

EXAMPLE: Abby’s car has the colour red, where “colour red” is a property of the car instance.

4.13 sampled feature

The real-world domain feature of interest, such as a groundwater body, aquifer, river, lake, or sea, which is observed.

[ISO 19156:2011]

4.14 sampling feature

Feature, such as a station, transect, section or specimen, which is involved in making observations of a domain feature.

NOTE: A sampling feature is purely an artefact of the observational strategy, and has no significance independent of the observational campaign.

[ISO 19156:2011, definition 4.16]

4.15 schema <XML Schema>

XML document containing a collection of schema component definitions and declarations within the same target namespace.

Example Schema components of W3C XML Schema are types, elements, attributes, groups, etc.

NOTE: The W3C XML Schema provides an XML interchange format for schema information. A single schema document provides descriptions of components associated with a single XML namespace, but several documents may describe components in the same schema, i.e. the same target namespace.

 [ISO 19136:2007]

4.16 sensor

Type of observation procedure that provides the estimated value of an observed property at its output.

Note: A sensor uses a combination of physical, chemical or biological means in order to estimate the underlying observed property. At the end of the measuring chain electronic devices often produce signals to be processed.

[OGC SWE Common 2.0, definition 4.5.]

5.    Conventions

5.1    Requirements class

Each normative statement (requirement or recommendation) in this standard is a member of a requirements class. Each requirements class is described in a discrete clause or sub-clause, and summarized using the following template:

All requirements in a class must be satisfied. Hence, the requirements class is the unit of re-use and dependency, and the value of a dependency requirement is another requirements class. All requirements in a dependency must also be satisfied by a conforming implementation. A requirements class may consist only of dependencies and introduce no new requirements.

5.2    Requirement

All requirements are normative, and each is presented with the following template:

where /req/[classM]/[reqN] identifies the requirement or recommendation. The use of this layout convention allows the normative provisions of this standard to be easily located by implementers.

5.3    Conformance class

Conformance to this standard is possible at a number of levels, specified by conformance classes (Annex A). Each conformance class is summarized using the following template:

All tests in a class must be passed. Each conformance class tests conformance to a set of requirements packaged in a requirements class.

W3C Schema (XSD) and ISO Schematron (SCH) files are considered as part of this standard, although available online only, due to concerns about document size. Many requirements are expressed in a single XSD or SCH file although tests are listed individually in the conformance annex (one test for XSD and one test for SCH). 

Schematron files explicitly specify which requirements are being tested in the title of the schematron pattern.

<pattern id="origin_elevation">
    <title>Test requirement: 
        /req/well-xsd/origin-elevation</title>
    <rule context="gwml2w:GW_Well">
        <assert
            test="count(gwml2w:gwWellReferenceElevation
            /gwml2w:Elevation[gwml2w:elevationType/
            @xlink:href=’http://www.opengis.net/
            req/well/origin_elevation’]) 
            = 1">A GW_Well needs at least one 
            origin Elevation</assert>
    </rule>
</pattern>

5.4    Identifiers

Each requirements class, requirement and recommendation is identified by a URI. The identifier supports cross-referencing of class membership, dependencies, and links from each conformance test to the requirements tested. In this standard, identifiers are expressed as partial URIs or paths, which can be appended to a base URI that identifies the specification as a whole in order to construct a complete URI for identification in an external context.

The URI for each requirements class has the form:

http://www.opengis.net/spec/groundwaterml/2.2/req/[classM].

The URI for each requirement or recommendation has the form:

http://www.opengis.net/spec/groundwaterml/2.2/req/[classM]/[reqN].

The URI for each conformance class has the form:

http://www.opengis.net/spec/groundwaterml/2.2/conf/[classM].

The URI for each conformance test has the form:

http://www.opengis.net/spec/groundwaterml/2.2/conf/[classM]/[testN].

5.5    External package abbreviations

Concepts from schemas defined in some other International Standards are designated with names that start with alpha codes as follow:

GF                   ISO 19109:2005 General Feature Model

GFI                 ISO 19156:2011 General Feature Model Instances

TM                 ISO 19108:2002 Temporal Schema, Temporal Objects

MD                 ISO 19115 Metadata

CV                   ISO 19123:2005 Schema for Coverage Geometry and Functions

OM                 ISO 19156:2011 Observations and Measurements

DQ                  ISO 19157:201X Data Quality

WML2                        OGC® WaterML 2.0: Part 1- Timeseries

GW                 GroundwaterML 2.0

TS                   TimeseriesML

5.6    Abbreviated terms

In this document the following abbreviations and acronyms are used or introduced: 

API                                    Application Program Interface

GeoSciML 3.2                   GeoScience Mark-up Language version 3.2

GeoSciML 4.0                   GeoScience Mark-up Language version 4.0

GML                                 OGC Geography Mark-up Language

GWML1                            Groundater Markup Language version 1.0 (Natural Resources Canada)

GWML2                            Groundwater Markup Language version 2.0 (this standard)

GWML2-Main                  UML Logical Model of the primary GroundWaterML2 elements (namespace http://www.opengis.net/gwml-main/2.2)

GWML2-Flow                  UML Logical Model of the elements required to capture groundwater flow (namespace http://www.opengis.net/gwml-flow/2.2)

GWML2-Constituent       UML Logical Model of the groundwater fluid body constituents and their relationships (namespace http://www.opengis.net/gwml-constituent/2.2)

GWML2-Well                   UML Logical Model of the features and properties associated with water well (namespace http://www.opengis.net/gwml-well/2.2)

GWML2-WellConstruction   UML Logical Model of the well drilling and construction details (namespace http://www.opengis.net/gwml-wellconstruction/2.2)

GWML2-AquiferTest       UML Logical Model of the features and properties associated with aquifer test (namespace http://www.opengis.net/gwml-aquifertest/2.2)

INSPIRE                            Infrastructure for Spatial Information in the European Community (Directive 2007/2/EC)

ISO                                    International Organization for Standardization

IUGS                                 International Union of Geological Sciences

NACSN                             North American Commission on Stratigraphic Nomenclature

NADM                              North American geological Data Model

OGC                                  Open Geospatial Consortium

O&M                                 OGC Observations and Measurements Conceptual Model

OMXML                          Observations and Measurements XML Implementation

SensorML                          Sensor Model Language

SOS                                    Sensor Observation Service

SWE                                   Sensor Web Enablement

TSML                                TimeseriesML

UML                                 Unified Modeling Language

UTC                                  Coordinated Universal Time

URI                                    Universal Resource Identifier

URL                                   Universal Resource Locator

WML2                               WaterML 2.0 – Part 1

XML                                 Extensible Markup Language

XSD                                   W3C XML Schema Definition Language

5.7    UML notation

The diagrams that appear in this standard, including the GWML2 Conceptual and Logical schemas, are presented using the Unified Modeling Language (UML), in compliance with ISO/IEC 19505-2.  

Note:Within the GWML2 conceptual and logical diagrams, the following color scheme is used to identify packages in some cases. This is just for information purposes.

Amber: GWML2 defined within this standard

Green and Purple: from GeoSciML 4.0

Blue: from O&M

5.8    Finding requirements and recommendations

This standard is identified as http://www.opengis.net/spec/groundwaterml/2.2. For clarity, each normative statement in this standard is in one and only one place, and defined within a requirements class table and identified with a URI, whose root is the standard URI. In this standard, all requirements are associated to tests in the abstract test suite in Annex A. using the URL of the requirement as the reference identifier. Recommendations are not tested but are assigned URLs and are identified using the ‘Recommendation’ label in the associated requirements table.

Requirements classes are separated into their own clauses, named, and specified according to inheritance (direct dependencies). The Conformance test classes in the test suite are similarly named to establish an explicit and mnemonic link between requirements classes and conformance test classes.

6.    Background

6.1    Technical Basis

This standard builds on a number of standards for encoding XML data, including:

• OMXML (OGC 10-025r1)
• sweCommon (OGC 08-094r1)
• GML  ISO 19136:2007 (OGC 07-036)
• ISO 19139 (Metadata)
• W3C XSD

This standard also builds on existing schema, primarily Observations & Measurements (OMXML) and GeoSciML 4.0 (OGC 16-008). It accomplishes this by (a) extending these schemas with groundwater specializations, (b) referring to a class in these schema in order to type a named property, or (c) using a class from the schemas as one of the two participants in a binary relationship.

6.2    Overview of Observations & Measurements

ISO19156 – Observations and Measurements is a generic GML schema for observations. As shown in Figure 1, it defines an observation as “…an act associated with a discrete time instant or period through which a number, term or other symbol is assigned to a phenomenon. It involves application of a specified procedure, such as a sensor, instrument, algorithm or process chain. The procedure may be applied in-situ, remotely, or ex-situ with respect to the sampling location. The result of an observation is an estimate of the value of a property of some feature.”

6.2.1    Sampling features

Sampling features in O&M are defined as a “feature, such as a station, transect, section or specimen, which is involved in making observations concerning a domain feature.” Sampling features in the groundwater domain are features along which, or upon, observations are made. The most relevant are water wells and boreholes, which effectively host observations along staged intervals; a collection of these intervals and their observations constitutes a log.

6.3    Overview of GeoSciML 4.0

GeoSciML 4.0 is a GML schema for core geological entities including geological units, structures, and earth materials. It is particularly relevant to GWML2 because bodies of rock serve as containers for subsurface water bodies. Such rock bodies possess variable hydrogeologic properties according to their material composition and topological organization. Thus, geological units and earth materials are the key GeoSciML 4.0 entities required by GWML2.

GeoSciML 4.0 defines a geological unit as “a body of material in the Earth whose complete and precise extent is inferred to exist (NADM GeologicUnit, Stratigraphic unit in sense of NACSN or International Stratigraphic Code), or a classifier used to characterize parts of the Earth (e.g. lithologic map unit like ‘granitic rock’ or ‘alluvial deposit’, surficial units like ‘till’ or ‘old alluvium’).”

GeoSciML 4.0 defines an earth material as “naturally occurring substance in the Earth” and intuitively refers to various types of rocks such as sandstone, granite, and gneiss.

7.    Conceptual Model

The GWML2 conceptual model is designed to be technology-neutral, and focused on the semantics of the groundwater domain. It consists of five components, as well as related properties and other entities: hydrogeological units, fluid bodies, voids, fluid flow, and wells. Conceptually, these entities form a simple template for a subsurface water container: the fluid container (a unit or its materials), the fluid itself (fluid body), the spaces in the container occupied by the fluid (void), the flow of fluid within and between containers and their spaces (flow), and the natural and artificial artifacts used to withdraw, inject, or monitor fluid with respect to a container (wells, springs, monitoring sites).

Well construction details are excluded from the conceptual model, but are included in the logical model for two reasons: (1) thematic, inasmuch as well construction was considered on the periphery of groundwater science, but important to resource management as well as important to significant data exchange scenarios, and (2) practical, as it is sufficiently modeled in GWML1 and could thus be directly imported with few changes. This eliminates the need for its re-conceptualization in the GWML2 conceptual model, keeping it tightly focused.

7.1    Hydrogeological Units

These are distinct volumes of earth material that serve as containers for subsurface fluids. The boundaries of a unit are typically discriminated from those of another unit using properties related to the potential or actual ability to contain or move water. The properties can be geological or hydraulic, and typically include influences from the surrounding hydrological environment. More specifically, the conceptual model delineates two types of hydrogeological units, with slightly different orientations: aquifer-related units have boundaries delimited by the hydrogeological properties of the rock body, while groundwater basins have boundaries delimited by distinct flow regimes. Aquifer-related units are subdivided into aquifer systems, which are collections of aquifers, confining beds, and other aquifer systems. Confining beds are units that impede water flow to surrounding units, and supersede notions such as aquitards, aquicludes, and aquifuges, which are not included herein, as it is difficult to differentiate these in practice.

Several significant properties are typically attributed to hydrogeological units, such as porosity, permeability, and conductivity, but these and others are modeled more accurately here as occurring necessarily concurrent with (dependent on) voids or fluid bodies. For example, porosity, in its various forms, requires both the presence of a unit (container) and its voids, as it is typically defined as the proportion of void volume to total unit volume (i.e. volume of solid material plus voids). Likewise, properties such as hydraulic conductivity and yield require the presence of units and fluid bodies, as they are concerned with the rate of movement of a fluid through a unit. Note that permeability and hydraulic conductivity are differentiated here: permeability refers to intrinsic permeability, which measures the ability of a unit to host fluid flow, independent of fluid properties and based solely on the connectivity and size of voids, whereas hydraulic conductivity additionally considers fluid properties.

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 (including organisms), 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 within the fluid.

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 its portion.

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, reservoir, canyon, flood plain, ground surface, 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.

Many of these concepts are depicted in Figure 2. Shown is a flow system (A+B) and two subsystems (A, B) that are its parts. Each subsystem is composed of interior flows, indicated by the solid lines with arrows, as well as input and output flows indicated as recharge and discharge, respectively. These flow systems are contained by three distinct hydrogeologic unit bodies, with the middle body oriented at an angle and having a K (hydraulic conductivity) value of 10^-5. Intraflow is exemplified by a flow line within the right hydrogeologic unit body, while Interflow is exemplified by the flow from right body (the source container) to middle body (the destination container). The boundary between the bodies serves as the interface through which the flow occurs. While not shown, the three hydrogeologic unit bodies contain a groundwater body (i.e. a fluid body) in their pores (i.e. voids), and it is this groundwater body that is flowing.

7.5    Wells

Well-related entities include water wells, springs, and monitoring sites. Water wells are man-made constructions for monitoring, withdrawing, or injecting water from/into a hydrogeological unit, while springs are features where water discharges to the surface naturally. Both wells and springs possess important links to the hydrogeological environment, including their host units and materials, as well as the intersecting fluid body. Monitoring sites are locations where devices are placed to measure various properties of significance to hydrogeology, such as water level, flow rate, water temperature, or chemical composition, or to take samples. As such, monitoring sites are roles played by other features, for example, water wells or springs.

7.6    Conceptual Model Specification

7.6.1    DocumentCitation

The class DocumentCitation is abstract, and has no attributes, operations or associations. It serves as a placeholder for legislative and reference documentation for a management area. Legislative documentation refers to the legal instrument or document that required the establishment of the management area. Reference documentation might describe the environmental objectives and measures that are to be undertaken in the management area to protect the environment (a reference to a management or action plan), licensing information, and associated maps.

The ‘Legislation References’ and ‘DocumentCitation’ classes from the INSPIRE Generic Conceptual Model are possible candidates for DocumentCitation.

7.6.2    Elevation

Elevation of a feature in reference to a datum.

7.6.3    GL_EarthMaterial

From GeoSciML 4.0:

Earth materials are substances, e.g. sandstone or granite, that constitute physical bodies, e.g. hydrogeological units. This class enables various hydrogeological properties to be attributed to a specific occurrence of a material, e.g. the sandstone of a specific aquifer.

7.6.4    GL_GeologicUnit

From GeoSciML 4.0:

Conceptually, may represent a body of material in the Earth whose complete and precise extent is inferred to exist (NADM GeologicUnit, Stratigraphic unit in sense of NACSN or International Stratigraphic Code), or a classifier used to characterize parts of the Earth (e.g. lithologic map unit like ‘granitic rock’ or ‘alluvial deposit’, surficial units like ‘till’ or ‘old alluvium’).

7.6.5    GW_Aquifer

A body of earth material that contains / potentially contains / potentially contained sufficient saturated permeable material to yield significant quantities of water to wells and springs (after Lohman, 1972).

7.6.6    GW_AquiferSystem

Aquifer system - a body of permeable and poorly permeable material that functions regionally as a water-yielding unit; it comprises two or more permeable beds separated at least locally by confining beds that impede groundwater movement but do not greatly affect the regional hydraulic continuity of the system; includes both saturated and unsaturated parts of permeable material (after ASCE, 1987).

7.6.7    GW_AquiferUnit

Denotes aquifer-related hydrogeological units: aquifer systems, aquifers, or confining beds.

7.6.8    GW_Basin

A large hydrogeologically defined body of ground typically consisting of hydraulically connected hydrogeological units, whose waters are flowing to a common or multiple outlets, and which is delimited by a groundwater divide.

7.6.9    GW_BiologicConstituent

Characterisation of the biological composition of the fluid body, both natural and man-made.

7.6.10    GW_ChemicalConstituent

Characterisation of the chemical composition of the fluid body, both natural and man-made.

7.6.11    GW_ConfiningBed

A layer of rock having very low porosity and in consequence hydraulic conductivity that hampers the movement of water into and out of an aquifer (Heath, 1983).

7.6.12    GW_Constituent

General (abstract) entity denoting a material, chemical or biological constituent of a fluid body.

7.6.13    GW_ConstituentRelation

Relation between fluid body components, typically caused by a specific mechanism, e.g. coating (from adsorption), constitution (from chemical bonding forming a new material), aggregation (from physical bonding, e.g. pressure), containment (from absorption, digestion).

7.6.14    GW_Discharge

An outflow of fluid from a container such as an aquifer, watershed, pipe.

7.6.15    GW_Divide

“A line on a water table or piezometric surface, on either side of which the groundwater flow diverges" (IGH0556).

7.6.16    GW_Flow

Process by which the fluid enters or exits a hydrogeological unit or a void, or flows within a unit or a void. Can flow from/to other natural or man-made features such as rivers, filtration stations, etc.

7.6.17    GW_FlowSystem

Flow path from recharge to discharge location, through hydrogeological units. It is related to a fluid body, and consists of a collection or aggregation of at least two specific flows, as well as possibly other flow systems.

7.6.18    GW_FluidBody

A distinct body of some fluid (liquid, gas) that fills the voids of a container such as an aquifer, system of aquifers, water well, etc. In hydrogeology this body is usually constituted by groundwater, but the model allows for other types of fillers e.g. petroleum.

7.6.19    GW_FluidBodyProperty

Additional properties that characterize a fluid body. Can include synoptic values for the whole body or location-specific observations such as age, temperature, density, viscosity, turbidity, color, hardness, acidity, etc.

7.6.20    GW_FluidBodySurface

A surface on a fluid body within a local or regional area, e.g. piezometric, potentiometric, water table, salt wedge, etc.

7.6.21    GW_HydrogeoUnit

Any soil or rock unit or zone that by virtue of its hydraulic properties has a distinct influence on the storage or movement of groundwater (after ANS, 1980).

7.6.22    GW_HydrogeoVoid

Voids represent the spaces inside (hosted by) a unit or its material. E.g. the pores in an aquifer, or in the sandstone of an aquifer. Voids can contain fluid bodies. Voids are differentiated from ‘porosity’ in that porosity is the proportion of void volume to total volume, while voids are the spaces themselves. Voids are required in GWML2, for example, to capture the volume of fractures in an aquifer.

7.6.23    GW_InterFlow

Fluid flow between features through an interface, exiting one feature and entering another. Features into which fluid is flowing are usually units, voids, or fluid bodies, but can be natural surface water features such as rivers or lakes, or even man-made features such as dams or canals. Likewise for features where water is exiting.

7.6.24    GW_IntraFlow

Fluid flow within a feature such as a unit, void, gw body, or even a man-made feature such as a conduit of some kind.

7.6.25    GW_Licence

Licence relating to the drilling of a well, the extraction of groundwater, etc.

7.6.26    GW_ManagementArea

The GW_ManagementArea represents an area of ground identified for management purposes. The area can be delineated by human factors such as policy or regulation concerns, as well as by domain concerns (in this case hydrogeological or hydrological). The spatial boundaries of a management area do not necessarily align exactly with associated hydrogeological feature boundaries. GW_ManagementArea has the potential to provide a pattern for a more generic OGC ‘trans-domain’ feature management class. GW_ManagementArea is equivalent to InspireAM:ManagementRestrictionOrRegulationZone.

7.6.27    GW_MaterialConstituent

Suspended or colloidal material in a fluid body, e.g sediment.

7.6.28    GW_Mixture

The nature of the inclusion of the constituent in the fluid body, e.g. suspension, emulsion, etc.

7.6.29    GW_MonitoringSite

Site of observation related to groundwater.

7.6.30    GW_Porosity

Measure of the proportion of the volume occupied by voids over the total volume of material including the voids. Voids are differentiated from ‘porosity’ in that porosity is a proportion, while voids are the spaces themselves. Types of porosity include: primary, secondary, dual, specific, effective, granular, fractured, karstic, etc.

7.6.31    GW_Recharge

Fluid added to an aquifer by various means such as precipitation, injection, etc.

7.6.32    GW_Spring

Any natural feature where groundwater flows to the surface of the earth. 

7.6.33    GW_UnitFluidProperty

A measured or calculated physical or hydraulic property that can be inherent in either an aquifer or its material, and some fluid body, e.g. hydraulic conductivity, transmissivity, storativity, permeability, porosity.

7.6.34    GW_UnitProperties

Additional properties of an aquifer not included in the model.

7.6.35    GW_UnitVoidProperty

Properties inherent in the relation between a hydrogeological unit and a void: includes the proportion of voids to the unit (porosity) or to the connectivity / size of void openings (intrinsic permeability).

7.6.36    GW_Vulnerability

The susceptibility of a feature to specific threats such as various physical events (earthquakes), human processes (depletion), etc.

7.6.37    GW_WaterBudget

An accounting of the water input and output of a hydrogeological unit, at a particular point in time or over a period of time, with a description of inflows and outflows.

7.6.38    GW_Well

A shaft or hole sunk, dug or drilled into the Earth to observe, extract or inject water (after IGH1397).

7.6.39    GW_Yield

Yield is the rate of fluid withdrawal associated with a unit, well, etc., expressed as m³. There are several types of yield, that can be considered: specific yield, sustainable yield, safe yield, aquifer yield, etc.

7.7    Requirements

Target logical models that are compliant with the conceptual model shall implement components of the conceptual model respecting their semantics, i.e. their definition and intent. In other words, the logical model must be highly semantically similar to components of the conceptual model and must not specify any requirements that would contradict or result in non-conformance to the conceptual model. Semantic similarity can be tested in multiple ways, including but not limited to: (i) direct comparison of UML components, (ii) comparison after mapping components to a common expressive knowledge representation language, such as first order logic or common logic, or (iii) comparison after mapping components to a reference ontology. The target can reuse and adapt existing logical models.

8.    Logical Model

The logical model incorporates all concepts from the conceptual model, and maintains their general intent. It differs from the conceptual model in its introduction of technology-specific artifacts from the OGC General Reference Model and derived schemas. These include additions such as classes, relations, properties, constraints, and usage principles. Another difference is the incorporation of the well construction package from GWML1.

The logical model is not a syntactical encoding, but is an OGC-compliant schema that is syntax-neutral. Syntactical encodings are derived from the logical model, such as the reference GML encoding described herein.

The addition of OGC constructs to the conceptual model amounts to the integration of several OGC-compliant GML schemas, primarily GeoSciML 4.0 and Observations & Measurements, but also MD_Metadata and others. These are adapted using the following strategies.

1.   HydrogeologicalUnit in GWML2 specializes GeologicUnit from GeoSciML 4.0, recognizing that in its most basic sense a hydrogeological unit is a body of rock (a geological unit) exhibiting some hydrogeological properties including possibly fluid storage and transfer.
2.   Water wells and boreholes specialize O&M:SF_SamplingCurve, which allows them to have a shape described by 3D points at the start and end of each segment along the well or borehole. Wells and boreholes differ by purpose and use: boreholes are physical engineering artifacts consisting of a hole and potentially materials fitted inside the hole for some human use, and wells are constructions for the extraction or injection of water from/into the ground, and have specific hydrogeological properties such as water yield and intended use. As a consequence, well and associated borehole lengths can differ for the same well. A well can be seen as a specific role played by a borehole.
3.   Property values are assigned datatypes from O&M: properties that can be numeric and/or categorical are assigned the OM_Observation datatype. Two factors compel this choice: method metadata can be added to each value to describe determination of the value, and each property can be further soft-typed for greater precision. An example of the latter is the porosity property, which in pratice could refer to any of a wide range of porosity types such as effective porosity, primary porosity, or secondary porosity.
4.   Fluid body constituent values are modeled as observations: for example, a chemical analysis of a groundwater sample might be represented in the following way:
   • Each measured value is the result of an observation;
   • The observedProperty would be e.g. “As_Concentration;” and
   • The featureOfInterest would be an instance of e.g. GW_ChemicalConstituent with ChemicalTypeTerm = “As” and gwState = “solid”.

   This approach is quite flexible: it allows for different mixture types (e.g. suspension, solution, emulsion), states (i.e. liquid, solid, gas), and measurement types (e.g. concentration) for a constituent type (e.g. “As”).

5.   Aquifer Tests are completely modelled using O&M, except for the single signature class GW_AquiferTest. This class is a property-less extension of O&M Sampling Feature.  The logical model for Aquifer Test is thus the O&M logical model, as illustrated further in Figure 17. Time series generated by aquifer tests are represented using TimeseriesML1.0 (OGC 15-042r2).
6.   DocumentCitation is replaced by Any type (i.e. the ‘documentation’ role is assigned a datatype of Any), in order to satisfy the original intention of the DocumentCitation class of enabling re-use of relevant classes from other schemas. This allows, for example, use of classes such as GW_Licence, MD_Metadata, INSPIRE’s DocumentCitation or LegislativeReferences.
7.   If an entity in the logical model is stereotyped as GMF_Feature (from the OGC General Feature Model), then any name, description and identifier attributes from the conceptual model are replaced by equivalents from GMF_Feature (e.g. GW_FluidBody::gwBodyDescription maps to AbstractFeature::description).

The logical model is organized into six application schema packages, as mentioned in Section 1.

1. GWML2-Main: core items, e.g. aquifers, their pores, fluid bodies, and management areas.
2. GWML2-Constituent: the biologic, chemical, and material elements of a fluid body.
3. GWML2-Flow: fluid flow within and between containers, and water budgets.
4. GWML2-Well: water wells, springs, and monitoring sites.
5. GWML2-WellConstruction: the components used to construct a borehole or well.
6. GWML2-AquiferTest: aspects associated with an aquifer test.

Because most of the differences between the logical and conceptual model can be inferred directly from the logical model UML diagrams, all diagrams are included below. Complete class descriptions are subsequently included only for additions or alterations to the conceptual model. Additions primarily include borehole construction elements and geology logs, while the alterations mainly consist of a cardinality revision: all attributes and relations are now optional, primarily to enable sparse encodings that avoid empty data fields if so desired.

8.1    Logical Model Specification

8.1.1    BoreCollar

Topmost component of a borehole construction.

8.1.2    Borehole

General term for a hole drilled in the ground for various purposes such extraction of a core, release of fluid, etc.

8.1.3    Casing

Collection of linings of the borehole.

8.1.4    CasingComponent

A single part of a borehole casing.

8.1.5    ConstructionComponent

Elements used in borehole construction.

8.1.6    Equipment

Equipment installed in a borehole (like a pump or any other device).

8.1.7    Filtration

Collection of filtration components used to filter a fluid body in a well.

8.1.8    FiltrationComponent

Material used to filter the fluid in a borehole or well.

8.1.9    GW_GeologyLog

Specialization of the OM_Observation containing the log start and end depth for coverages.

For Stratigraphic logs the observedProperty will be a GeoSciML 4.0:GeologicUnit/name.

For Lithologic logs the observedProperty will be a GeoSciML 4.0:GeologicUnit/composition/CompositionPart/material.

8.1.10    GW_GeologyLogCoverage

A particular collection of values that represent the group of measurements taken in intervals along the length of the log. Overrides DiscreteElementCoverage to enable LogValues to be elements of the collection (GeologyLogCoverage).

8.1.11    LogValue

The value of the log property at a depth interval along the log.

8.1.12    Screen

Collection of components of the water pump screen.

8.1.13    ScreenComponent

Component of the well lining where water enters the well.

8.1.14    Sealing

Collection of materials that prevent undesirable elements from entering the borehole or well.

8.1.15    SealingComponent

A material used for sealing the construction of a borehole or well.

8.1.16    WellConstruction

Construction components of the well. These are particularly important when assessing results of pump tests.

9.    Requirements Classes (normative)

This section describes requirement classes for any target implementation conforming to GWML2.  Target implementations must meet related conformance class tests for at least one concrete requirements class (in Sections 9.2 and greater).  The core requirement class (Section 9.1) is abstract, therefore solely meeting the core requirements is insufficient to claim compliance with GWML2. Note, this section documents only those requirements that cannot be read directly from the UML logical model—the logical model denotes the first suite of canonical requirements, which are supplemented by those below.

9.1    Abstract requirements classes: GWML2 core logical model

This core requirement class describes requirements that must be met by all target implementations that claim compliance with GWML2 (this standard).  It also sets common requirements for all extensions of this standard.  Since this requirement class is abstract, a conformant target implementation SHALL also implement at least one concrete requirements class from Sections 9.2 and greater.

The properties, constraints, cardinalities and associations documented in the UML will be honoured by all the target implementations.

9.1.1    Quantities

The Quantities and Measurements units of measure shall be taken from a standard vocabulary governed by an appropriate community.

9.1.2    Code lists

All properties that should use formal vocabularies are modelled in UML as classes having the stereotype <<CodeList>>.  The list of valid terms should be taken from a standard vocabulary governed by an appropriate community. Vocabulary term identifiers should be HTTP URI conformant to RFC 3986.

9.1.3    Code list URIs

The URI used to identify vocabulary terms SHOULD be resolvable using Linked Data Principles, such that a URI identifier can resolve to multiple representations (or formats) for the term using HTTP content codings, MIME-type, and language negotiation mechanisms.

9.1.4    Identifiers

Features that use an HTTP URI as their identifier SHALL be resolvable following Linked Data principles (the HTTP URI is a link to possibly multiple representations of the resource). It is expected that a HTTP URI that is a feature identifier can be used to extract one or more representations of that feature by deferencing that URI, because the URI represents both its online location and its identity.

9.1.5    Feature

A valid instance document SHALL contain at least one valid GWML 2.2 feature.

9.2    Requirement class: GWML2-Main

9.2.1    Feature of interest for Association classes

OM_Observation is extensively used to represent property values wherever it is useful to include supporting metadata such as the methods used to obtain the values.  As stated in ISO19156/OGC 10-004r3, the OM_Observation’s feature of interest should be the bearer of the observed property (10-004r3, clause 7.2.2.7). All properties in GWML 2.2 that use OM_Observation in the model are carried by Features; the relationship between the observation and the bearer of properties is obvious, except for two cases: GW_UnitFluidProperty (Figure 18)andGW_UnitVoidProperty (Figure 19).

GW_FluidProperty is an association class linking a GW_HydroGeoUnit and a GW_FluidBody and carries properties that are inherently related to the association of a geological unit and the fluid occupying its voids.  Not being a feature, this class cannot be the feature of interest of the properties it bears.

Traditionaly, those properties (gwHydraulicConductivity, gwStorativity, gwTransmissivity and gwYield) are assigned by convenience to the hydrogeological unit (GW_HydrogeoUnit), because the fluid is a body of groundwater (GW_FluidBody) that is rarely explicitly identified. Therefore, the feature of interest of all the values of GW_UnitFluidProperty SHALL be the GW_HydrogeoUnit instance at the gwFluidBodyUnit end of the GW_UnitFluidProperty association.

Similarly, GW_UnitVoidProperty is an association class linking a GW_HydroGeoUnit with a GW_HydrogeoVoid, and this association class also then cannot be the feature of interest for the properties it bears (Figure 19). 

As void properties are traditionally assigned to the hydrogeologic unit, the feature of interest of all property values of GW_UnitVoidProperty SHALL be the GW_HydrogeoUnit instance, which is located at the gwVoidUnit end of the GW_UnitVoidProperty association.

9.3    Requirement class: GWML2-Constituent

Analytical results are modelled as OM_Observation having GW_Constituent as features of interest (see Figure 20).  A typical analytical procedure involves a sampling feature (such as a SF_Specimen) and a series of OM_Observations reporting on some properties of the feature of interest.

By referring to the real world identifiable feature using the sampledFeature property, and using the observation’s featureOfInterest to refer to the constituent of the fluid body, this pattern permits a detailed description of the composition of various parts of the fluid body.

9.4    Requirement class: GWML2-Flow

This requirements class does not contain any requirement.  All the requirements are inherited from /req/core and /req/constituent.

9.5    Requirement class: GWML2-Well

This clause describes groundwater abstraction and monitoring through artificial features (water wells, monitoring stations) and natural features (springs).  Artificial features are modelled as O&M sampling features (by the ISO-19156 definition) as they are used as support for observations.

9.5.1    Water wells

The shape of the well is a 3D curve, in absolute coordinates, that represents the path of the hole in the ground.  However, it is common practice to position observations, construction artefacts, and properties of the surrounding materials along this 3D path using a 1D coordinate system relative to the beginning of the hole.  Although most wells are often assumed to be straight vertical bores, this standard allows for the generic case, where the well path is not a straight line, and therefore any such property or element needs to refer to the well path to calculate its absolute position.

This standard also provides alternative representations for commonly used origin elevations, such as the location of the well on the surface of the earth, the location and elevation of the well collar, the reference elevation for down hole properties, etc.  Note that the reference elevation and the well path are distinct reference elements but it is best practice to ensure that the reference elevation point intersect the path.  Because of the variety of practices and because the reference elevation can actually change over time (replaced headwork, subsidence, etc.) it is not always possible to have a definitive reference elevation.

Several GW_Well features need to be located relative to the well path:

• GW_GeologyLog LogValue
• Construction elements
• Any related Observation
• Any related SamplingFeature

The following set of requirements defines how to report these values:

The elevation CRS must be a relevant EPSG vertical (1 dimension) CRS. Example: EPSG:5100 (Mean Sea Level : http://epsg.io/5100-datum).

9.5.2    Well shape

9.5.3    Relative position

The relative positions of all elements positioned relative to the 3D shape shall be calculated from the origin point of that shape, which is the first vertex of the shape.

The relative position is the linear distance along the bore path, expressed as a positive value, using the uom inferred from the CRS of the shape z axis (metres or feet in the vast majority of cases). Different GW_Well elements may have different ways to encode the relative positions.

9.5.3.1    Observations

Any Observation that needs to be positioned along the well must provide a reference geometry (a GM_Curve) and a position along that curve.  In a case where the path is the path of the well or a borehole, the reference geometry is expected to be the shape of the well or the borehole, but it is not required.  For instance, the relative location can be a “virtual path” somewhat related to a well or a group of wells.

The relative position shall be encoded in a specially named NamedValue.

9.5.3.2    Related SamplingFeature

Any sampling feature that must be positioned along the linear path shall encode the reference GM_Curve and the relative position using sams:parameter

The relative position shall be encoded in specially labelled NamedValue.

9.5.4    Geology Log

GW_GeologyLog is an OM_Observation, with a start and end depth, that shall capture downhole geological observations (including geophysical and geochemical) using the gwml:gwWellGeology property rather than other OM_Observation properties.

The geologic log is encoded as a GW_GeologyLogCoverage.

The GW_GeologyLogCoverage/LogValue is positioned at the origin of the support feature, which is a SF_SamplingCurve.

Depth shall be expressed as linear distance from the first vertex of the GM_Curve.  When the featureOfInterest is a GW_Well, the origin is implicitly gwWellLocation + gwWellReferenceElevation:elevation.

The fromDepth must be nearest the reference elevation.

9.5.5    Monitoring Sites

Elevation CRS must be a relevant EPSG vertical (1 dimension) CRS. Example EPSG:5100 (Mean Sea Level : http://epsg.io/5100-datum).

9.6    Requirement class: GWML2-WellConstruction

9.6.1    Borehole

BoreCollar:collarElevation CRS must be a relevant vertical (1 dimension) CRS. Example EPSG:5100 (Mean Sea Level : http://epsg.io/5100-datum).

9.6.2    Construction

Borehole shall identify a BoreCollar that must be used as the reference location.  The reference BoreCollar shall have a collarElevationType equal to http://resource.gwml.org/def/collarElevationType/originElevation.

Note that this BoreCollar need not be a physical feature, but would normally coincide with one.  In a typical instance, we would find 2 or more collars, one or more real physical features, and another one as the reference collar that might or might not match one of the physical collars.

The Borehole shape SHALL be a 3D geometry that represents the complete well that includes any construction elements above the ground.

Depth shall be expressed as linear distance from the Borehole shape’s first vertex. 

The ‘from’ value must be closer to the Borehole origin than the ‘to’ value.

9.7    Requirement class: Vertical Well (profile)

A vertical well is a special case where the shape of the well is a straight vertical line.  The rationale to create a special profile is to inform the data consumer that calculation of relative position into absolute position is greatly simplified.  Vertical wells are very common and several groundwater applications expect them to be vertical.   

GW_Well:shape shall have only 2 vertices.

The second vertex shall have the same x and y as the first vertex.

9.8    Requirement Class: GeologyLog (profile)

This requirement class describes the recommended pattern to encode a GeologyLog.

Geological logs are modelled as GML discrete coverages (CV_DiscreteElementCoverage) of elements of type LogValue.  Each Log Value is composed of a pair of properties to locate the element along the Well path (fromDepth and toDepth) and a SWE DataRecord that contains an arbitrary set of fields to report properties of interest along the path (see Figure 21).

SWE (Clause 7.3 of OGC 08-094r1) describes the requirements to encode a DataRecord. A community that defined a common Geologic Log encoding should agree on a definition and scoped name for the DataRecord, and definitions of the individual fields composing the record.

For example, a community that wants to use a GeoSciML 4.0 vocabulary to encode a geology log can agree on a field type (eg: SWE Category) and a definition (a URI) to flag that field in the DataRecord as having controlled content.  Another community might chose to constrain the complete DataRecord by agreeing on the scoped name of the DataRecord itself.

9.9    Requirement class: Aquifer test (profile)

Aquifer hydraulic parameters are routinely evaluated by a series of tests that involves pumping or injecting water at known rates and by observing the changes in the water table.  Other tests might involve injecting a tracer (radio element or dye) at some location and follow its progression at observation points.  From these observations, various methods have been developed to compute aquifer properties.  To adequately report an aquifer test, the data about initial conditions, test parameters, sampling features, measured and calculated observation must be packaged and put into context.  

Figure 17, above, shows the elements required to encode an aquifer test. An AquiferTest assesses an Aquifer using a method (eg: Packer test) that is encoded as an OM_Process.  The test is performed at a test site (the GW_AquiferTest defines a geometry corresponding to the test location) and consists of sampling features (usually the GW_Well) that are associated to the GW_AquiferTest through relatedSamplingFeature.  Each sampling feature has a role in the test (observation or test features). Some sampling features are sites where test activities are performed (referred to as “test feature”), such as pumping water out of a bore. Other features are sites where more passive observations are made, such as measuring the impact of pumping made at the test sampling feature on the water table. From this activity, a series of observation are made, typically time series along the timespan of the test. Then from these observations, a method is used to infer some aquifer properties (such as transmissivity, storativity or yield).  The findings are then documented in a report that can be attached to GW_AquiferTest using generic metadata properties.

A typical AquiferTest might be sketched as follows in Figure 22:

9.9.1    Aquifer Test O&M mapping

Observation and Measurement (O&M 2.0 : OGC 10-004r3), along with its GWML extensions, contains all the elements needed to model an aquifer test.  A complete aquifer test can be built around SF_SamplingFeature and OM_Observation, with the addition of GW_AquiferTest, a subtype of SF_SpatialSamplingFeature (Figure 23), to distinguish aquifer tests from other sampling features and to package observations and sampling features.  

9.9.2    GW_AquiferTest  (O&M profile)

GW_AquiferTest is a specialized sampling feature representing an aquifer test (or pump test). It packages all the sampling features and observations generated by the test and the computed results from those observations.  The following section describes implementation of aquifer test in O&M. 

9.9.3    SF_SamplingFeature properties

9.9.3.1    sampledFeature

In the context of an aquifer test, it links to the real world feature being assessed by the aquifer test (generally a GW_AquiferUnit).  O&M does not constrain SF_SamplingFeature to any particular feature type, but this standard requires that the sampledFeature shall be a subtype of a GW_HydrogeoUnit.

9.9.3.2    relatedSamplingFeature

In the context of an aquifer test, the related sampling feature property identifies all the sampling features participating in the aquifer test. The role of each feature is assigned by the SF_SamplingFeatureComplex:role property. The role of the sampling feature is scoped by the test. Therefore the same sampling feature can have different roles in different tests, but also within the same test (by having multiple SF_SamplingFeatureComplex referring to the same SF_SamplingFeature). Single bore tests are examples where the observation bore and the test bore are the same feature. This standard proposes a list of core roles to identify the observation features and test features.

The test feature is the “active” sampling feature where the test is performed (e.g. the well that is pumped or injected).

The observation feature is the “passive” feature where observations are made. It is the feature at which the effects of the test are measured.

A single sampling feature can be the target of several SF_SamplingFeatureComplex.  A data provider can add more than one SF_SamplingFeatureComplex to accommodate other roles (see Figure 24).

9.9.3.3    parameter

Test parameters, such as pumping rates during the test are not considered as being an observation, but as test parameters.  To document test parameters, there are two options:

·      Using SF_SpatialSamplingFeature:hostedProcedure of type OM_Process that can encode all possible details of a test using SensorML (OGC 12-000), MD_Metadata (ISO-19115) or any other suitable model. 

·      Use parameter of type SF_SamplingFeature:parameter:NamedValue using agreed value types for well-known test parameters.

Although the formal mechanism to report test parameters is through OM_Process, this standard recommends reporting community defined values in  simple parameter key-value pairs (KVP) using sf:NamedValue.

9.9.3.4    relatedObservation

All related observations, including the observations made at the test feature sites and observation derived from those observations should be available as related observations (sf:relatedObservation). 

From the raw observations measured during a test, new observations can be inferred or calculated.  The raw observations (related from the observation Features) and the derived observations (the result of the test) SHALL be related to each other using om:ObservationContext.  The role of the observation context defines which observation derives or supports the other one. ‘supportObservation’ and ‘derivedObservation’ roles can be considered complementary: if A is supportObservation of B, then B is the derivedObservation of A.

9.9.3.5    hostedProcedure

A hostedProcedure is used to document such things as methods to identify or localise the sampling feature, but its use is not constrained to anything specific.  The hostedProcedure property, of type OM_Process, may be used to accommodate detailed aquifer test parameters if needed by the data provider. 

The O&M standard does not prescribe any model to encode OM_Process, but suggests:

ISO 19115-2 provides MI_Instrument, LE_Processing and LE_Algorithm, which could all be modelled as specializations of OM_Process. OGC SensorML [16] provides a model which is suitable for many observation procedures

OGC 10-0043 / ISO-19156, clause 7.2.3, p. 14

For instance, a pump (used to pump water from the borehole) can be modelled as a SensorML sml:PhysicalSystem.

9.9.3.6    shape

SF_SpatialSamplingFeature does not constrain the geometry type (Point, Curve, Polygon, etc), therefore any geometry can represent a test.  In most situations, the geometry of the test is the test area, the zone of influence around the pumping test or even the volume of rock affected or in scope for the test.

This standard also does not constrain the geometry type.  Communities that wish to constrain the geometry type should create a profile of this standard.

9.9.4    OM_Observation

OM_Observations are used to represent values of properties observed or computed in the context of this test. There are at least two categories of observations generated through an aquifer test:

• Raw observations, normally taken at the observationFeatures; and
• Derived observations, calculated from the raw observations.

These two kinds of observations differ by their respective feature of interest. For the former (raw data) the feature of interest is the sampling feature from which observations are made (e.g. observation bore).  In the latter case, the feature of interest is the GW_AquiferTest itself.  Observations can be linked together using related observations (om:relatedObservation/om:ObservationContext), which provide a role (om:ObservationContext/om:role) for the targeted observation.  Figure 25 shows an example of “raw” observations (Drawdown1 and Drawdown2) measured at two observation wells (obs1 and obs2). The same figure also shows a derived observation (transmissivity) having the aquifer test itself as its feature of interest.  The derived observation provides a link back to the supporting observation used to compute the derived values.

Observations made during the test and computed observations are modelled as OM_Observations.

9.9.4.1    phenomenonTime, resultTime and validTime

As specified in Observation and Measurement; phenomenonTime reflects the time that the result applies to the property; the resultTime is the time at which the value has been obtained or became available and validTime is the time during which the value is usable.  Depending on the type of observation (raw or computed), those time might be different (see Table 2).

9.9.4.2    observedProperty

This property describes the phenomenon being observed (e.g. groundwater level).  The observed property is normally a reference to a property inherent in the feature of interest (“the real word feature is the subject of the observation and carries the observed property, OGC-10-004r3, clause 7.2.2.7).   But because of subtle variations in the semantics of such properties (such as specific Yield versus maximum Yield versus sustainable Yield, etc.), the observedProperty meaning should be formally defined by a community.  The value of observedProperty becomes a reference to that definition (expressed in SWE, SKOS or OWL for example).

ObservedProperty can also be a compound property (a collection of observedProperty).  Again, because of the close tie to use cases, compound properties should be defined by a community.

9.9.4.3    result

The result property reports the product of the observation process. In many cases, the aquifer test will produce a time series, such as drawdown data over time. When the result is a time series, it shall be modelled as a TimeSeriesML 1.0 (OGC 15-082r3).

Derived (or computed) observations will often produce compound values. It is possible to report each result component as distinct observations, but GWML2 shall use the more efficient alternative of wrapping compound results into swe:DataRecord.

9.9.5    Aquifer test overview

Figure 26 provides an example of the mapping of AquiferTest to O&M.

10.    XML Implementation (normative)

10.1    GWML2-XSD

Groundwater features and their properties will be encoded in XML using standard GML encoding rules (Annex E of OGC Geography Markup Language v3.2 (ISO 19136:2007). 

In examples, HTTP URIs that are used as resolvable resources (e.g. for vocabularies) are encoded using the DTD entity resource.gwml.org to avoid binding the examples to a specific URI.  Full instance documents will have an entity declaration in the xml header in the form.

XML snippets will use the following prefixes:

ISO-19136_2007 provides a mapping between UML classifiers and XSD entities.  All XSD types and elements must be created following those mapping rules.  This standard considers the XSD files (the schema files) to be normative (they contain the official interpretation of 19136 conversion of the UML classifiers into XML). 

Other rules, that can’t be expressed in XSD, are provided as schematron rules.  As the XSD files, schematron rules files are considered normative.

The date-time formats will conform to ISO standards.  Although this is already a GML 3.2.1 encoding rule (clause 14.2.2.7), this format shall also be used in any string that is not normally checked for an occurrence of dates.

Note that this precludes the use of time-coordinate systems such as UNIX time. This is specified in order to be maximally consistent with WML2 requirements. The time zone will be included in the time element.

Greenwich Mean Time (GMT or Zulu)

<om:phenomenonTime>
       <gml:TimeInstant gml:id="ab.ww.402557.wl.1.ti.1">
              <gml:timePosition>1981-09-12T00:00:00Z</gml:timePosition>
       </gml:TimeInstant>
</om:phenomenonTime>

Time Zone (example is Newfoundland time zone -3:30)

<om:phenomenonTime>
       <gml:TimeInstant gml:id="nf.ww.34212.wl.1.ti.1">
              <gml:timePosition>1981-09-12T00:00:00-03:30</gml:timePosition>
       </gml:TimeInstant>
</om:phenomenonTime>

Some SWE Common types are restricted to avoid ambiguity.

10.1.1    Identifier

A feature that can be accessed through Linked Data using a resolvable HTTP URI must use this HTTP URI as its global unique identifier.  In GML, this shall be  encoded using gml:identifier and code space = “http://www.ietf.org/rfc/rfc2616”.  In other words, the gml:identifier shall point to a representation of itself. 

Example of a feature that exposes its resolvable HTTP URI as a globally unique identifier

(…)
<gwml2w:GW_Well gml:id="ca.ab.gov.wells.402557">
<gml:description>Water well from Alberta water well database</gml:description>
       <gml:identifier codeSpace="http://www.ietf.org/rfc/rfc2616">http://ngwd-bdnes.cits.nrcan.gc.ca/Reference/uri-cgi/feature/gsc/waterwell/ca.ab.gov.wells.402557</gml:identifier>
       <gml:name codeSpace="urn:cgi:featureType:CA.AB:WaterWell">402557</gml:name>
       <gml:name codeSpace="urn:x-gin">ca.ab.waterWell.402557</gml:name>
(…)

10.1.2    By-Reference properties

Properties can be constrained to be by-reference only, or either inline or by-reference.  For a by-reference property that refers to an external feature, the reference shall be resolvable over the web.  The reference shall be either a resolvable HTTP URI that might also match the feature’s globally unique identifier (see /req/core/identifier)or an HTTP request (for instance, a WFS GetFeature with the stored query “urn:ogc:def:query:OGC-WFS::GetFeatureById”) to the a representation of the feature in GML. 

(…)
<gwml2:gwAquiferSystemPart 
  xlink:href="http://environment.data.gov.au/groundwater/feature/hydrogeologicalunit/hgu.nsw.5"
  xlink:title="Stuarts Point - Lower Quaternary Sands"/>
(…)

Note that elements under GWML2 namespaces can be mixed with other namespaces. For example, this standard does not have a dependency to WFS, but GWML can be serialised in a WFS document, along with features from other domains.  Failure to validate such a document does not necessarily mean that the GWML XML requirements are not met, as other external indirect instances might fail.  Therefore, this requirement class only addresses instances of GWML in an XML document.

All property by reference using xlink:href should provide a human readable label in xlink:title.

Example of a casing material showing the use of xlink:href (/req/xsd-xml-rules/vocabulary-references ) and xlink:title (/req/xsd-xml-rules/xlink-title):

<gwml2wc:casingMaterial 
  xlink:href="http://www.sandre.eaufrance.fr/?urn=urn:sandre:donnees:154::CdElement:5:::referentiel:3.1:xml" xlink:title="PVC"/>

Vocabulary references for all classes of stereotype «CodeList» are implemented as gml:Reference using xlink:href and ought to be a resolvable URI in the form of an HTTP URL.

10.2    Requirement class:  GWML2-Main XML encoding

All xml elements under namespace http://www.opengis.net/gwml-main/2.2 must validate against the schema located at http://schemas.opengis.net/gwml/2.2/gwml2-main.xsd. 

OM_Observation values, used as property values in GW_UnitFluidProperty must identify the instance of GW_HydrogeoUnit at the gwFluidBodyUnit end of the association between this feature and the GW_FluidProperty

<?xml version=“1.0” encoding=“UTF-8”?>
<gwml2:GW_Aquifer gml:id="aq.1">
       <gsmlb:geologicUnitType xlink:href="http://www.opengis.net/def/gwml/2.2/geologicunitype/aquifer_unit" xlink:title="Aquifer" xsi:type="gwml2:AquiferPropertyType"/>
       <!– (…) –>
       <gwml2:gwUnitFluidBody>
              <gwml2:GW_UnitFluidProperty>
                      <gwml2:gwYield>
                             <om:OM_Observation gml:id="aq.1.fp.1">
                                    <om:phenomenonTime>
                                           <gml:TimeInstant gml:id="aq.1.fp.1.ti.1">
                                                  <gml:timePosition>2015/7/28T12:00:00Z</gml:timePosition>
                                           </gml:TimeInstant>
                                    </om:phenomenonTime>
                             <!– (…) –>
                                    <om:featureOfInterest xlink:href="#aq.1" xlink:title="aquifer 1"/>
                             <!– (…) –>
                             </om:OM_Observation>
                      </gwml2:gwYield>
                      <gwml2:gwUnitFluidBody xlink:href="http://resource.org/id/fluid-body/fb1" xlink:title="fluid body f1"/>
                      <gwml2:gwFluidBodyUnit xlink:href="#aq.1" xlink:title="aquifer 1"/>
              </gwml2:GW_UnitFluidProperty>
       </gwml2:gwUnitFluidBody>
</gwml2:GW_Aquifer>

OM_Observation values, used as property values in GW_UnitVoidProperty must identify the instance of GW_HydrogeoUnit at the gwVoidUnit end of the association between this feature and the GW_VoidProperty

<?xml version=“1.0” encoding=“UTF-8”?>
<gwml2:GW_AquiferSystem gml:id="as.1">
       <!– (…) –>
       <gwml2:gwUnitVoid>
              <gwml2:GW_UnitVoidProperty gml:id="v1">
                      <gwml2:gwPorosity>
                             <om:OM_Observation gml:id="aq.1.fp.1">
                                    <om:phenomenonTime>
                                           <gml:TimeInstant gml:id="aq.1.fp.1.ti.1">
                                                  <gml:timePosition>2015/7/28T12:00:00Z</gml:timePosition>
                                           </gml:TimeInstant>
                                    </om:phenomenonTime>
                                    <!– (…) –>
                                    <om:featureOfInterest xlink:href="#as.1" xlink:title="Aquifer System 1"/>
                                    <!– (…) –>
                             </om:OM_Observation>
                      </gwml2:gwPorosity>
                      <gwml2:gwUnitVoid xlink:href="http://www.opengis.net/def/nil/OGC/0/unknown" xlink:title="Unknown"/>
                      <gwml2:gwUnitVoid xlink:href="#as.1" xlink:title="Aquifer System 1"/>
              </gwml2:GW_UnitVoidProperty>
       </gwml2:gwUnitVoid>
</gwml2:GW_AquiferSystem>

10.3    Requirement class: GWML2-Constituent XML encoding

All xml elements under namespace http://www.opengis.net/gwml-constituent/2.2 must validate with the schema located at http://schemas.opengis.net/gwml/2.2/gwml2-constituent.xsd. 

10.4    Requirement class: GWML2-Flow XML encoding

All xml elements under namespace http://www.opengis.net/gwml-flow/2.2 must validate with the schema located at http://schemas.opengis.net/gwml/2.2/gwml2-flow.xsd. 

10.5    Requirement class: GWML2-Well XML encoding

All xml elements under namespace http://www.opengis.net/gwml-well/2.2 must validate with the schema located at http://schemas.opengis.net/gwml/2.2/gwml2-well.xsd. 

Well shall provide an origin elevation as a reference for relative positions along the borehole path.

Elevation geometries must have a relevant vertical 1D srsName.

Examples of reference elevations (measured using different methods); note, one of them is designated as the origin (‘reference’) elevation for relative positions:

<gwml2w:gwWellReferenceElevation>
    <gwml2w:Elevation>
        <gwml2w:elevation srsDimension="1" 
            srsName="http://www.opengis.net/def/crs/EPSG/0/5711" 
            uomLabels="m AHD">139.06</gwml2w:elevation>
        <gwml2w:elevationAccuracy 
            xlink:href="http://www.opengis.net/def/nil/OGC/0/unknown" 
            xlink:title="unknown"/>
        <gwml2w:elevationType 
            xlink:href="http://www.bom.gov.au/water/groundwater/ngis/elevation-type/natural-ground-surface" 
            xlink:title="natural ground surface"/>
        <gwml2w:elevationMeasurementMethod 
            xlink:href="http://www.bom.gov.au/water/groundwater/ngis/elevation-method/dem" 
            xlink:title="Digital Elevation Model"/>
    </gwml2w:Elevation>
</gwml2w:gwWellReferenceElevation>
<gwml2w:gwWellReferenceElevation>
    <gwml2w:Elevation>
        <gwml2w:elevation srsDimension="1" 
            srsName="http://www.opengis.net/def/crs/EPSG/0/5711" 
            uomLabels="m AHD">139.06</gwml2w:elevation>
           <gwml2w:elevationAccuracy 
            xlink:href="http://www.opengis.net/def/nil/OGC/0/unknown" 
            xlink:title="unknown"/>
           <gwml2w:elevationType 
            xlink:href="http://resource.gwml.org/def/elevationType/originElevation" 
            xlink:title="reference elevation"/>
           <gwml2w:elevationMeasurementMethod 
            xlink:href="http://www.bom.gov.au/water/groundwater/ngis/elevation-method/dem" 
            xlink:title="Digital Elevation Model"/>
    </gwml2w:Elevation>
</gwml2w:gwWellReferenceElevation>

10.5.1    Well shape

The CRS of the shape must be a 3D CRS that is coherent with the planar CRS of gwWellLocation and the elevation CRS of origin Elevation.

Example of a well shape represented as a vertical line, using a relevant srsName:

<sams:shape>
    <gml:Curve gml:id="ab.ww.402557.shape.1" 
        srsDimension="3" srsName="urn:ogc:def:crs:EPSG:4955">
           <gml:segments>
               <gml:LineStringSegment>
                   <gml:posList>49.671622 -114.625045 0.00 
                       49.671622 -114.625045 11.58</gml:posList>
               </gml:LineStringSegment>
           </gml:segments>
    </gml:Curve>
</sams:shape>

10.5.1.1    Observations

Any observation that is positioned relative to a geometry, such as well or borehole path, SHALL identify the geometry as a spatial reference

The relative position of the observation must be encoded in the om:parameter using a specific encoding.

Example of Observation positioned along the path of a bore: