Groundwater body characterisation for Water Framework Directive implementation: catchment trials in Scotland and Northern Ireland
Background to Research: Research into methodologies and trialling methodologies for characterising groundwater bodies as part of the implementation of the Water Framework Directive.
Objectives: To provide methodology for characterising groundwater bodies and carry out characterisation exercises to test the methodologies.
Key words: groundwater body characterisation, characterisation trialling.
Scotland and Northern Ireland differ from England and Wales in that they do not have CAMS and in general there is less data available with which to characterise groundwater bodies. Initial definition is based on as large an area of ground as possible. Following the Water Framework Directive (WFD) definition, all rock types in Scotland and Northern Ireland are aquifers, although till may be a non-aquifer in Northern Ireland in line with current thinking in the Republic of Ireland. In addition Ireland prefers to separate out superficial aquifers such as gravel from bedrock aquifers such as basement. Generally, islands included in groundwater characterisation are those where the population suggests that greater than 10 m3/d is abstracted (i.e. 50 people).
A generic classification of the aquifer types provides a first pass at identifying groundwater bodies, albeit at a coarse scale. Initial characterisation considers location of boundaries, pollution and abstraction pressures, and the nature of the superficial cover, if any. It also requires an assessment of the risk of the body failing the objectives laid down in Article 4 of the WFD, the quantitative condition tested with a water balance calculation and a conceptual model, the chemical condition is still subject to guidance to be issued by the UK Groundwater Task Team but aims to assess the risk of failing to meet status rather than to assess status.
The methodology has been trialled in two catchments, one relatively data rich in Scotland and one, relatively data poor in Northern Ireland. The approach to the Northern Irish Catchment, the Oona catchment in the Upper Bann, is strictly in the spirit of the WFD. The Scottish catchment, the Almond, has been carried out more from a traditional hydrogeological stance, i.e. collect all the data available and collate it to provide a hydrogeological description of the catchment. There are, therefore, some elements of data described in the Almond trial which are not actually used in the characterisation process.
The Oona study is a preliminary assessment, for the purposes of developing the methodology. The wider application of the methodology to other catchments is discussed. A GIS was used to manage, display and analyse the data. The reporting structure is two-stage, comprising a summary table listing the required data, and accompanying more detailed descriptions, where necessary, based around the same headings.
The methodology recognises that initial decisions on whether groundwater bodies are at risk of failing to meet the objectives of the Water Framework Directive will, at times, need to be pragmatic, due to lack of data, constraints on time and resources, and consequent limitations in understanding of catchment hydrogeology. However, trialling the methodology in the Oona Water catchment has shown that even with limited data it is possible to build up a conceptual model of a groundwater body that in most cases is likely to provide sufficient understanding to make an initial assessment of whether the body is at risk. This assessment includes an indication of the degree of confidence with which it is made, based on the amount and quality of the data behind the assessment.
It is recommended that the collation and processing of the relevant data sets are done as far as possible for the whole of Northern Ireland in one step, rather than individually for each catchment (as was necessary for the Oona Water trial). Once this is done, the critical stage of populating the summary table of data is not a lengthy process. In most cases, the data included in the summary table will largely be sufficient to allow initial ‘At Risk’ assessments to be made with a moderate degree of confidence. Only for bodies where confidence levels are too low for comfort, for example because the hydrogeology is thought to be particularly complex and there are limited supporting data, will it be necessary to go into more detail.
The River Almond catchment in Central Scotland forms part of a larger body. However, for the purposes of trialling the methodology it is typical of the environment found in Central Scotland and forms a useful test catchment. The catchment offers a variety of rock and superficial types, urban, industrial and agricultural provinces and former mine workings. It was found that data were adequate to carry out a water balance and to construct a conceptual groundwater flow model of the catchment. Again a GIS approach was found most suitable for the data handling and presentation. There are no identified significant quantitative pressures in the Almond catchment and the groundwater body is not considered to be at risk. Within the limits of the trial, the chemical status of the catchment is, however, considered to be at risk.
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