Groundwater Resources Bedrock Aquifers 1:100,000 Ireland (ROI) ITM

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Groundwater is the water that soaks into the ground from rain and can be stored beneath the ground. An aquifer is a body of rock and/or sediment that holds groundwater. There are two main types of aquifer in Ireland – bedrock aquifers, and sand and gravel aquifers.

Bedrock is the solid rock at or below the land surface. Over much of Ireland, the bedrock is covered by materials such as sands and gravel. The sands and gravels occur naturally on top of the bedrock. They were laid down by meltwater from melting ice sheets, by rivers, or by wind.

There are two main types of bedrock aquifer. In most of them, groundwater flows through fractures and fissures. In about half of the limestone rocks, groundwater flows through cavities and caves. This type of limestone is called karst.

Not all sand and gravel layers are aquifers. This is because some of them are very thin or are dry. If the sands and gravels are saturated with water, they have the potential to supply large volumes of water through wells or springs.

The aquifer maps show the potential of areas in Ireland to provide water supplies. There are three main groups based on their resource potential:

Regionally important – the aquifers are capable of supporting large public water supplies sufficient to support a large town;

Locally important – the aquifers are capable of supporting smaller public water supplies or group schemes;

Poor – the aquifers are only capable of supporting small supplies, such as houses or farms, or small group schemes.

The three main groups are broken down into nine aquifer categories in total. Please read the lineage for further details.

Information used to assign bedrock aquifer categories include: rock type (Hydrostratigraphic Rock Unit Groups - simplified bedrock geology with similar hydrogeological properties), yield (existing wells and springs), permeability and structural characteristics. All of the information is interpreted by a hydrogeologist and areas are drawn on a map to show the aquifers.

This Bedrock Aquifer map is to the scale 1:100,000 (1 cm on the map relates to a distance of 1km).

It is a vector dataset. Vector data portray the world using points, lines, and polygons (areas).

The bedrock aquifer data is shown as polygons. Each polygon holds information on the aquifer code, description, rock unit name, rock unit description, Hydrostratigraphic Rock Unit Group Name, Hydrostratigraphic Rock Unit Group Changes, Bedrock Geology 100k newcode, stratigraphy code (rock layers with age profile), lithology code (rock type), Aquifer Category Original and Comments.

Geologists record information about how thick the sand and gravel layers on top of the bedrock are. They also note down how big the different grains of sand and gravel are. Information from quarries and deep pits is used. Information from boreholes (a deep narrow round hole drilled in the ground) is also used. All of the information is interpreted by a hydrogeologist and areas are drawn on a map to show the aquifers GSI Aquifer classes are divided into three main groups based on their resource potential (Regionally or Locally important, or Poor), and further subdivided based on the type of openings through which groundwater flows (through fissures, karst conduits or intergranular). There are nine aquifer categories in total.

This is a polygon dataset containing nine Bedrock Aquifer classes. Scale: 1:100,000

1) Regionally Important Aquifers: Regionally important aquifers are capable of supplying regionally important abstractions (e.g. large public water supplies), or excellent yields (>400 m3/d). Bedrock aquifer units generally have a continuous area of >25 km2 and groundwater predominantly flows through fractures, fissures, joints or conduits. Regionally important sand/gravel aquifers are >10 km2, and groundwater flows between the sand and gravel grains. This group is subdivided into the following types: Rk Regionally Important Karstified Bedrock Aquifer Rf Regionally Important Fissured Bedrock Aquifer Rg Regionally Important Sand/Gravel Aquifer Regionally important karstified aquifers may be further subdivided based on the whether groundwater flows mainly through conduits (Rkc) or more diffusely through solutionally-enlarged fissures (Rkd).

2) Locally Important Aquifers: Locally important aquifers are capable of supplying locally important abstractions (e.g. smaller public water supplies, group schemes), or good yields (100-400 m3/d). In the bedrock aquifers, groundwater predominantly flows through fractures, fissures, joints or conduits. Locally important sand/gravel aquifers are typically >1 km2, and groundwater flows between the sand and gravel grains. This group is subdivided into the following types: Lm Locally Important Bedrock Aquifer, Generally Moderately Productive Ll Locally Important Bedrock Aquifer, Moderately Productive only in Local Zones Lk Locally Important Karstified Bedrock Aquifer Lg Locally Important Sand/Gravel Aquifer

3) Poor Aquifers:

These bedrock aquifers are capable of supplying small abstractions (e.g. domestic supplies, small group schemes), or moderate to low yields (<100 m3/d). Groundwater predominantly flows through a limited and poorly-connected network of fractures, fissures and joints. This group is subdivided into the following types: Pl Poor Bedrock Aquifer, Generally Unproductive except in Local Zones Pu Poor Bedrock Aquifer, Generally Unproductive

The Aquifer maps along with the Groundwater Vulnerability map and Source Protection Area maps are merged to produce Groundwater Protection Zones. Each zone enables an assessment of the risk to groundwater, independent of any particular hazard or contaminant type. The Groundwater Protection Zones form one of two components of Groundwater Protection Schemes. A Groundwater Protection Scheme provides guidelines for the planning and licensing authorities in carrying out their functions, and a framework to assist in decision-making on the location, nature and control of developments and activities in order to protect groundwater. Use of a scheme will help to ensure that within the planning and licensing processes due regard is taken of the need to maintain the beneficial use of groundwater. Groundwater Protection Schemes are county-based projects that are undertaken jointly between the GSI and the respective Local Authority. The groundwater protection scheme comprises two components: * A land surface zoning map (or maps) called the groundwater protection zone map, and * Groundwater protection responses for existing and new potentially polluting activities. The role of the GSI is in the production of the land surface zoning map, whereas decisions on groundwater protection responses are the responsibility of the statutory authorities.

Data Resources (4)

SHP
ESRI Shapefile
DATA VIEWER
Data Viewer
ESRI REST
ESRI REST

Data Resource Preview - ESRI REST

Theme Science
Date released 2003-01-21
Date updated 2021-10-22
Dataset conforms to these standards The INSPIRE Directive or INSPIRE lays down a general framework for a Spatial Data Infrastructure (SDI) for the purposes of European Community environmental policies and policies or activities which may have an impact on the environment.
Rights notes ['Creative Commons Attribution 4.0 International (CC BY 4.0)', 'Data that is produced directly by the Geological Survey Ireland (GSI) is free for use under the conditions of Creative Commons Attribution 4.0 International license.\n\nhttps://creativecommons.org/licenses/by/4.0/\n\nhttps://creativecommons.org/licenses/by/4.0/legalcode\n\nUnder the CC-BY Licence, users must acknowledge the source of the Information in their product or application.\n\nPlease use this specific attribution statement: "Contains Irish Public Sector Data (Geological Survey Ireland) licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) licence".\n\nIn cases where it is not practical to use the statement users may include a URI or hyperlink to a resource that contains the required attribution statement.', 'license']
Update frequency Other
Language English
Landing page https://gsi.geodata.gov.ie/portal/apps/webappviewer/index.html?id=d333a8a9b6ab44378411fc0d973db4ef
Geographic coverage in GeoJSON format {"type":"Polygon","coordinates":[[[-10.47472, 51.44555],[-10.47472, 55.37999], [-6.01306, 55.37999], [-6.01306, 51.44555], [-10.47472, 51.44555]]]}
Spatial Reference Systems (SRS) Irish Transverse Mercator (ITM, EPSG:2157)
Vertical Extent {"verticalDomainName": "sea level", "minVerticalExtent": "0", "maxVerticalExtent": "0"}
Provenance information Bedrock Aquifers The process of assigning each aquifer to an appropriate category is termed ‘aquifer classification’. The detailed criteria and process can be found here: https://www.gsi.ie/en-ie/publications/Pages/GSI-aquifer-classification-flowchart.aspx. Bedrock aquifer classification is based firstly on the rock type (lithology), and the 1:100,000 simplified bedrock map is used as a basis. This dataset is called the Hydrostratigraphic Rock Unit Groups 1:100,000 Ireland (ROI) ITM, which was generalised to 27 hydrostratigraphic units. Yield is one of the main concerns in aquifer development projects, yields from existing wells are conceptually linked with the main aquifer categories: • Regionally important (R) aquifers should have (or be capable of having) a large number of ‘excellent’ yields: in excess of approximately 400 m3/d (4,000 gph). • Locally important (L) aquifers are capable of ‘good’ well yields 100-400 m3/d (1,000-4,000 gph). • Poor (P) aquifers would generally have ‘moderate’ or ‘low’ well yields - less than 100 m3/d. However, existing well yield information is often difficult to use because reliable, long term yield test data are quite rare (particularly for the less productive aquifers). In practice, then, the following criteria are used in aquifer classification: • Permeability and transmissivity data from formal pumping tests, where discharge and water levels readings have been taken over a period of many hours or days. • Productivity data from wells where either formal pumping tests have been undertaken or where at least one combined reading of discharge and drawdown data are available. The GSI has developed the concept of ‘productivity’ as a semi-quantitative method of utilising limited well test data (Wright, 2000). A ‘productivity index’ is assigned to a well from one of five classes: I (highest), II, III, IV, and V, using a graphical comparison of well discharge with specific capacity. • Occurrence of springs with ‘high’ flows (greater than 2160 m3/day total flow). • Occurrence of wells with ‘excellent’ yields (greater than 400 m3/day discharge). • Hydrological information such as drainage density where overlying strata are thin, and baseflows or flows in rivers (better aquifers will support higher baseflows and summer flows). • Lithological and/or structural characteristics of geological formations which indicate an ability to store and transmit water. Clean washed and sorted sands and gravels for example, are more permeable than poorly sorted glacial tills. Clean limestones are also more permeable than muddy limestones. Areas where folding and faulting has produced extensive joint systems tend to have higher permeabilities than areas where this has not occurred. • Aquifer assessments from Groundwater Protection Schemes in neighbouring counties and from existing reports. All seven factors are considered together; productivity and permeability data are only given ‘precedence’ over lithological and structural inferences where sufficient data are available. Data from neighbouring counties in similar geological environments are included. Some bedrock units have been grouped if they are of similar geological age and have similar lithological/structural characteristics. In considering the classifications provided, it is important to note that: • The bedrock aquifer classifications are based on the bedrock units mapped by the Bedrock Section of the Geological Survey Ireland at 1:100,000 scale - Bedrock Geology 1:100,000 Ireland (ROI) ITM There are seven bedrock aquifer categories: Regionally Important Aquifers: can support regionally important abstractions (e.g. large public water supplies), or give excellent yields (>400 m3/d). Bedrock aquifer units generally have a continuous area of >25 km2 and groundwater predominantly flows through fractures, fissures, joints or conduits. Regionally important sand/gravel aquifers are >10 km2, and groundwater flows between the sand and gravel grains. This group is subdivided into the following types: • Rk Regionally Important Karstified Bedrock Aquifer • Rf Regionally Important Fissured Bedrock Aquifer Regionally important karstified aquifers can be subdivided if it is known that groundwater flows mainly through conduits (Rkc) or more diffusely through solutionally-enlarged fissures (Rkd). Locally Important Aquifers: can support locally important abstractions (e.g. smaller public water supplies, group schemes), or give good yields (100-400 m3/d). In the bedrock aquifers, groundwater predominantly flows through fractures, fissures, joints or conduits. Locally important sand/gravel aquifers are typically >1 km2, and groundwater flows between the sand and gravel grains. This group is subdivided into the following types: • Lm Locally Important Bedrock Aquifer, Generally Moderately Productive • Ll Locally Important Bedrock Aquifer, Moderately Productive only in Local Zones • Lk Locally Important Karstified Bedrock Aquifer Poor Aquifers: are capable of sustaining small abstractions (e.g. domestic supplies, small group schemes), or moderate to low yields (<100 m3/d). Groundwater predominantly flows through a limited and poorly-connected network of fractures, fissures and joints. This group is subdivided into the following types: • Pl Poor Bedrock Aquifer, Generally Unproductive except in Local Zones • Pu Poor Bedrock Aquifer, Generally Unproductive All work on the data was carried out in ArcGIS. In 2021, the data structure was reviewed and a new database was created in ArcGIS Enterprise. Using ArcGIS Pro 2.6.3, the dataset was renamed as part of a GSI data standardisation process. A standardised dataset alias was added. A unique id field was added. A new unique identifier was added for each record using an attribute rule. Most fields were renamed and an alias added. Domains were created for relevant fields to ensure attribute integrity for those fields. The attribute values can only be added from pre-defined GSI tables in the form of drop-down values. Attribute rules were set up to automatically insert certain values eg unique identifier. The data was cleaned using a GSI notebook. This checked the attribute values contained valid domain values and a spell check was carried out. Some manual cleaning of obvious errors was also carried out. Metadata was updated to new GSI standard. Aquifer Geological Lines 1:100,000 Ireland (ROI) Originally, the lines were hand drawn on paper maps. All bedrock 100k map sheets (21) are available in paper copy accompanied by a geological report. Phase 1: The 21 paper maps covering Ireland were digitised. Each map was manually digitised using AutoCAD 12.0 software. Several layers of data were created for each map sheet: Stratigraphy, Lithology, Igneous, Diagenetic, Dynamic, Thermal, Linework and Point symbols and stored in .dwg format. The data was registered to the OSi 1:100,000 digital rasters. The data was clipped to the OSi coastline (high water mark). Water bodies such as lakes were also clipped. Irish National Grid (IG) projection. Phase 2: Data was converted to ArcInfo coverages (1994-2003) IG AutoCAD layers were converted to .dxf format and imported into ArcInfo 7.x. Coding was used to attach attribute information to the data layers from the bedrock lexicon table. A legend was generated. The ArcInfo coverages were converted to shapefiles. Phase 3: Borders and overlaps between map sheets were removed. IG. ArcGIS 8.x and Microsoft Access were used. Access was used to join additional attributes to the data layers including a unique code called NEWCODE. ArcGIS 8.x was used to manually remove borders and overlaps and to fill gaps. Work was carried out by GIS staff in close collaboration with bedrock geologists. The final product was quality checked by bedrock geologists. A stylefile was generated. Shapefiles produced were: 1) Final100kunion.shp - A polygon shapefile that contains bedrock geological information on Stratigraphy, Igneous, Lithology and Diagentic codes, their unit names and descriptions, 2) Index100Map.shp – A polygon index of 1:100,000 scale map sheets to allow sheet number identification at 100,000 scale. 3) Final100kstruc.shp (Structural Linework) - A line shapefile that contains structural geological linework codes and descriptions. 4) Final100kstra.shp (Stratigraphic Linework) - A line shapefile that contains stratigraphic geological line codes and descriptions. 5) Cross100ksection (Cross sections) - A line shapefile that contains map sheet cross sections as per paper printed maps and provides links to the cross sections in image format. 6) Final100kmin.shp - A point shapefile containing selected mineral and quarry descriptions from Bedrock 1:100,000 map series. In 2021, the data structure was reviewed and a new database was created in ArcGIS Enterprise. Using ArcGIS Pro 2.6.3, the dataset was renamed as part of a GSI data standardisation process. A standardised dataset alias was added. A unique id field was added. A new unique identifier was added for each record using an attribute rule. Most fields were renamed and an alias added. Domains were created for relevant fields to ensure attribute integrity for those fields. The attribute values can only be added from pre-defined GSI tables in the form of drop-down values. Attribute rules were set up to automatically insert certain values eg unique identifier. The data was cleaned using a GSI notebook. This checked the attribute values contained valid domain values and a spell check was carried out. Some manual cleaning of obvious errors was also carried out. Metadata was updated to new GSI standard.
Period of time covered (begin) 2005-01-07
Period of time covered (end) 2019-09-11