GSI Groundwater Recharge Mapping

Theme: Science
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The national Groundwater Recharge Map depicts estimated recharge to the deep groundwater system, i.e. groundwater that can be tapped as the sustainable resource.

The main hydrogeological controls on groundwater recharge include subsoil permeability, subsoil thickness, saturated soils, and the ability of the underlying aquifer to accept percolating waters. Estimated groundwater recharge is lowest in areas overlain by thick, low permeability clay. Where lower productivity aquifers underlie the land surface, a recharge cap is applied to simulate rejected recharge, even where subsoils are thin. This reflects the limited ability of these aquifers to accept and transmit recharging waters.

The map is derived from existing hydrogeological and meteorological data layers: annual rainfall, annual estimated actual evapotranspiration (AE), soil drainage, subsoil permeability, groundwater vulnerability, peat, sand/gravel aquifer, bedrock aquifer class.

The layers are overlain and interpreted using the guidelines (GW 5) outlined by the Irish Working Group on Groundwater (WGGW, 2005), subsequently revised in Hunter Williams et al (2011) and Hunter Williams et al (2013). The combination of hydrogeological layers gives a particular hydrogeological scenario that is related to a recharge coefficient. The recharge coefficient is the proportion of effective rainfall that can potentially become recharge. The map of recharge coefficients is combined with the effective rainfall map and the recharge cap to produce the groundwater recharge map.

Utilities of the map include: aquifer water balance assessments using simple lumped models or distributed numerical groundwater models; assessment of the impact of groundwater abstractions as required under the European Water Framework Directive; and delineation of source protection zones.

Outer and inner ranges for the groundwater recharge coefficients are defined, to be used depending on the hydrogeology of the study area. Users should be aware that the map uses the central value of the inner recharge coefficient range, and the 30 year average effective rainfall (1971-2000, Met Eireann). Thus, groundwater recharge may be over- or under-estimated, depending on local conditions

Users should also be aware that the recharge cap applied to poorly productive aquifers may need further examination for particular studies; that karst aquifer resources may be overestimated due to low storage within these aquifers; that only diffuse recharge is modelled and point and allogenic recharge are not accounted for in the groundwater recharge map; that the influence of the water table depth and ground slope are not accounted for.

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Theme Science
Date dataset released 2012-01-17
Date dataset updated 2016-11-18
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 license conditions apply', '', 'license', '', 'license']
Update frequency Annual
Language English
Landing Page
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) TM75 / Irish Grid (EPSG:29903)
Vertical Extent {"maxVerticalExtent": "1041", "verticalDomainName": "sea level", "minVerticalExtent": "0"}
Provenance information Application of the data: Local details are generalised to fit the original mapping and interpretation scale of 1:50,000. Evaluation of specific sites and circumstances will normally require further and more detailed assessments, and will often require site investigations. Sources of Information: Teagasc/EPA 1:40,000 Subsoil Map + Teagasc/EPA soils 1:40,000 GSI 1:50,000 Subsoil Permeability Map from county GWPSs and NDP-funded national mapping programme GSI 1:50,000 groundwater vulnerability map. GSI 1:100,000 Bedrock Aquifer map GSI 1:50,000 Sand and Gravel Aquifer map Met Eireann 1971-2000 Rainfall + AE Groundwater Recharge map creation technique: Created using tools built though ArcGIS model builder. On a county by county basis. In order for the Recharge map to be created, the recharge coefficient has to be calculated. This calculation depends on a large combination of conditions that are worked out from overlaying the following layers through a combination of unioning, intersecting, adding fields and calculating fields: 1. Teagasc Soils: For indicating areas of Peat and whether soil is wet or dry. 2. Teagasc Subsoils: For indicating sand and gravel soils. 3. Permeability 4. Vulnerability 5. Sand & Gravel Aquifers 6. National Aquifer dataset 7. Effective Rainfall (Met Eireann) The Recharge Map Creation tool goes through several different geoprocessing tasks. For each county: 1. Selecting the county: Union the Teagasc soil, sub-soil, Permeability and Vulnerability layers. 2. Unioning and intersecting with Fixed layers: -Intersecting Sand and Gravel Aquifer: This data will be included for analysis along with the Sand and Gravel soils from the Teagasc subsoils layer. -Intersecting National Aquifer: This layer will be used to calculate what cap (if any) will be applied to the potential recharge mm amount. -Aquifers of type LL, PU and PL will entail a capping on this final recharge figure. (100 or 200 mm/yr) 3. A hydrological Category is applied according to combination of values for each record. A recharge Coefficient is then calculated. 4.The final recharge value is calculated as Effective Rain amount x the %Recharge Coefficient. For further Information got to
Period of time covered (begin) 2009-01-13
Period of time covered (end) 2012-01-09