Groundwater is the water that soaks into the ground from rain and is stored beneath the ground. An aquifer is a body of rock and/or sediment that holds groundwater. The process of rain filling up an aquifer is called ‘recharge’.

The Groundwater Recharge map shows the amount of rainfall which reaches the stores of groundwater (the ‘aquifers’) across Ireland. The amount of recharge was calculated over the period 1981-2010 and then averaged to give a yearly amount.

Geological information is interpreted by hydrogeologists to create the map includes soil drainage, subsoil type, subsoil permeability, subsoil thickness, groundwater vulnerability and aquifers. The amount of rain falling on the land minus how much of that rain is taken up by plants is also a factor that determines how much groundwater recharge there is at a particular location. This is known as the ‘effective rainfall’.

Different combinations of the geological factors give 24 hydrogeological scenarios. There is a ‘recharge coefficient’ for each scenario, which is the percentage of the ‘effective rainfall’ that may become groundwater recharge. Using ArcGIS software, the data are merged to create areas on a map to show the recharge. Please read the lineage for more detail.

This map is to the scale 1:40,000. This means it should be viewed at that scale. When printed at that scale 1cm on the map relates to a distance of 400m.

It is a vector dataset. Vector data portray the world using points, lines, and polygons (areas). The recharge data is shown as polygons. Each polygon holds information on:

Average Recharge (mm/yr) - average annual recharge to the groundwater aquifer across that polygon

Recharge Coefficient (%) – the proportion of effective rainfall that becomes groundwater

Effective Rainfall (mm/yr) – the rainwater remaining after plants have taken up some of the rainfall

Recharge Pre Cap (mm/yr) - effective rainfall x recharge coefficient, not limited by maximum recharge capacities

Recharge Cap Apply – is there a maximum amount of recharge that the aquifer can accept? (Yes/ No)

Recharge Maximum Capacity (mm/yr) – the maximum amount of recharge the aquifer can accept. Only applies to bedrock aquifers of category Ll, Pl, or Pu.

Average Recharge Range (mm/yr) - Annual Recharge (mm) categorised into a range of values used to style the map.

Hydrogeological Setting Code - determined by the combinations of different geological layers

Hydrogeological Setting Description – the description of the main geological layers that combine to let different amounts of rainfall through to become groundwater

Vulnerability Category – the code for the groundwater vulnerability

Vulnerability Description – the groundwater vulnerability description

Soil Drainage – whether the soil is well drained or poorly drained

Subsoil Type (Quaternary Sediment Code) – the code for the subsoil type

Subsoil Description (Quaternary Sediment Description) – description of the subsoil type

Sand/Gravel Subsoil – whether the subsoil is sand/gravel or not

Subsoil Permeability Code - the code for the permeability of the subsoil

Subsoil Permeability Description – description of the subsoil permeability

Sinking Stream – indicates the presence of a stream that sinks fully or partially into the ground. Derived from the Groundwater Vulnerability 40K mapping.

Sand and Gravel Aquifer Category –Sand and Gravel Aquifer Category from Groundwater Resources (Aquifers) 40K mapping

Sand and Gravel Aquifer Description –Sand and Gravel Aquifer Description from Groundwater Resources (Aquifers) 40K mapping

Bedrock Aquifer Category –Bedrock Aquifer Category from Groundwater Resources (Aquifers) 100K mapping

Bedrock Aquifer Description –Bedrock Aquifer Description from Groundwater Resources (Aquifers) 100K mapping

Hydrostratigraphic Rock Unit Group Name– Rock Unit Groups that have hydrogeological significance

County – Irish County