The current national map of sand and gravel aquifers is variable in terms of the level of information available for each body as different areas have been delineated based on different mapping programmes and strategies. Much of the available Quaternary and subsoil mapping of the country indicates sand and gravel as a geological stratum just below the surface. 'Full' Quaternary stratigraphic mapping, showing the three-dimensional extent of these sands and gravels bodies, has not been completed in many areas. There are thus sands and gravels deposits 'hidden' beneath till across the country, and there are discontiguous areas separated by peat/cutover peat and till. Other occurrences of new, discrete sand and gravel bodies have only been recently discovered.
The definition of sand and gravel groundwater bodies for the initial WFD characterisation was desk-study based with a reliance on the surface extents from the original Teagasc mapping and its inherent methodology. Further characterisation is required to provide field evidence on the true nature of these deposits in the third dimension. As well as mapping extent and depth of the bodies, the investigations consider the hydraulic properties; important for example in examining how sands and gravels along and underneath water courses controls flow in the water course.
The programme comprises three phases:
- Desk study and fieldwork preparation;
- Fieldwork including mapping, data collection; and
- Data collation, analysis and reporting.
The sand and gravel field mapping regions from 2015 to 2017 are shown below: