Historic General Quality Assessment (GQA) Headline Indicators of Water Courses - Chemistry
The General Quality Assessment (GQA) Headline Indicator scheme or GQAHI (previously known as GQA) was the national indicator for water quality in rivers and canals. It was designed to provide an accurate and consistent assessment of the state of water quality and how it changes over time. These assessments were made for Biological, Chemical and Nutrients and undertaken for discrete river stretches. This datasets relates to the chemical assessments. In Wales we maintained the full GQA network until 2010 based on 800 sampling sites which provided information for approximately 4700km. Grades of river quality for the chemical GQA, Chemical grade Likely uses and characteristics:en - A: Very good, All abstractions, Very good Salmonid fisheries, Cyprinid fisheries, Natural ecosystems. - B: Good, All abstractions, Salmonid fisheries, Cyprinid fisheries, Ecosystems at or close to natural. - C: Fairly good, Potable supply after advanced treatment, Other abstractions, Good Cyprinid fisheries, Natural ecosystems, or those corresponding to good Cyprinid fisheries - D: Fair, Potable supply after advanced treatment, Other abstractions, Fair Cyprinid fisheries, Impacted ecosystems. - E: Poor Low grade abstraction for industry, Fish absent or sporadically present, vulnerable to pollution, Impoverished ecosystems - F: Bad, Very polluted rivers which may cause nuisance, Severely restricted ecosystems *Provided other standards are met where the grade is caused by discharges of organic pollution.
- Identification
- Extent
- Distribution
- Quality
- Keywords
- Spatial Reference System
- Content
- Constraints
- Maintenance
- Metadata
Identification
- Identifier
- NRW_DS116325
- Alternative Title
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- AfA162 Historic GQA Headline Indicators of Water Courses – Chemistry
- Metadata Language
- English
- Lineage
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Chemistry GQAHI/GQA sites were sampled twelve times a year, the samples being taken at the same spot on each sampling occasion to ensure consistency. In Wales each chemical sample was measured for biochemical oxygen demand (BOD), ammonia and dissolved oxygen (the most common types of organic pollution from sewage treatment works, agriculture and industry). A category was assigned using three years worth of samples for each sampled chemical and assigned a category assessed against chemical standards expressed as percentiles The data collected over three years were used to determine average nutrient concentrations. So the classification for the year 2008 includes the results for 2006 and 2007. Subsequently a category was assigned to each length of river according to the lowest standard achieved by any of the two or three measurements. The Chemistry GQA used in Wales described quality in terms of three chemical measurements that detect the most common types of organic pollution from sewage treatment works, agriculture and industry. In 2007 the GQA river network was reduced to the GQAHI river network. The assessment was changed to be based on total ammonia and dissolved oxygen only. Biochemical oxygen demand (BOD) was removed from the assessment and all past grades re-calculated. The data described have been amended to be consistent and comparable for all years.
- Dataset Reference Date (Publication)
- 2016-07-01
Extent
Extent
- Geographic Extent
- Wales (WLS)
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Distribution
Distribution
- Format Type and Description
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Documents
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- Specification
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Excel
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Documents
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)
- Resource Locator
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Download Data
World Wide Web page
Quality
Data quality
- Quality Scope
- Dataset
- Conformity
- Commission Regulation (EU) No 1089/2010 of 23 November 2010 implementing Directive 2007/2/EC of the European Parliament and of the Council as regards interoperability of spatial data sets and services
- Explanation
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This dataset has not been assessed for conformance to the referenced INSPIRE regulation.
- Degree
- false
- Lineage
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Chemistry GQAHI/GQA sites were sampled twelve times a year, the samples being taken at the same spot on each sampling occasion to ensure consistency. In Wales each chemical sample was measured for biochemical oxygen demand (BOD), ammonia and dissolved oxygen (the most common types of organic pollution from sewage treatment works, agriculture and industry). A category was assigned using three years worth of samples for each sampled chemical and assigned a category assessed against chemical standards expressed as percentiles The data collected over three years were used to determine average nutrient concentrations. So the classification for the year 2008 includes the results for 2006 and 2007. Subsequently a category was assigned to each length of river according to the lowest standard achieved by any of the two or three measurements. The Chemistry GQA used in Wales described quality in terms of three chemical measurements that detect the most common types of organic pollution from sewage treatment works, agriculture and industry. In 2007 the GQA river network was reduced to the GQAHI river network. The assessment was changed to be based on total ammonia and dissolved oxygen only. Biochemical oxygen demand (BOD) was removed from the assessment and all past grades re-calculated. The data described have been amended to be consistent and comparable for all years.
Keywords
Keywords
- Type
- Theme
Citation
- Date (Publication)
- 2008-06-01
Keywords
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NRW Thesaurus
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- water quality monitoring
- Type
- Theme
Citation
- Date (Publication)
- 2026-03-04
Spatial Reference System
- Code
- NONE
Content
Content Information
NRW Profile
Custom Elements
Constraints
Constraints
Limitations on Public Access and Use
- Restriction type
- Other restrictions
Access Constraints Directive
- Limitations
- no limitations
Access Constraints Text
- Other constraints
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There are no access restrictions on this data. NRW may release, publish or disseminate it freely.
Use Constraints
- Use constraints type
- Other restrictions
- Other constraints
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© CNC/NRW Data may be re-used under the terms of the Open Government Licence providing it is done so, acknowledging both the source and NRW's copyright. It is the recipient's responsibility to ensure the data is fit for the intended purpose. Attribution statement: Contains Natural Resources Wales information © Natural Resources Wales and Database Right. All rights Reserved.
Metadata
Metadata
- File Identifier
- 4f4c4942-4343-5764-6473-313136333235 XML
- Metadata Language
- English
- Parent Identifier
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Historic General Quality Assessment (GQA) Headline Indicators of Water Courses
NRW_DS118585
- Resource type
- Dataset
- Metadata Date
- 2026-06-26T08:09:27.559Z
- Metadata Standard Name
- NRW
- Metadata Standard Version
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1.0