Geology

Catchment geological maps and statistics were derived from British Geological Survey (BGS) datasets at 1:625000 scale.

Users should note that values for stations which are inside Northern Ireland but for which the catchment extends into the Republic of Ireland are likely inaccurate because the input geological data does not extend into the Republic of Ireland. This is indicated in catchment comments where appropriate.

Layers illustrating permeability can be displayed on each station details page. In collaboration with the British Geological Survey, a bespoke key has been agreed which emphasises the influence of hydrogeology on river flow behaviour (distinguishing, in particular, between permeable/impermeable bedrock). Catchment proportions of different aquifer types and permeability classes are available.

Hydrogeology

Proportions of the catchment underlain by rock formations of as defined in the BGS 1:625000 UK Hydrogeology Map (version 5) aquifer characterization and shown in the table below. Information from this layer should be preferred over the Bedrock layer mentioned below.

NRFA Hydrogeology Class
BGS Aquifer Characterisation
High
Highly productive aquifer
Low
Low productivity aquifer
Moderate
Moderately productive aquifer
Rock
Rocks with essentially no groundwater

Bedrock

Proportions of the catchment underlain by rock formations of high, moderate, very low, or mixed permeability based on classification of the BGS 1:625000 Bedrock layer (version 4) as indicated in the table below.

While statistics derived from the Bedrock geology dataset are provided for continuity, the statistics derived from the UK Hydrogeology map should be preferred when information about bedrock permeability is needed.

NRFA Bedrock Permeability Class
BGS Type
BGS Description
High
Extensive and highly productive aquifers
Aquifers in which flow is dominantly in fissures and other discontinuities
High
Extensive and highly productive aquifers
Aquifers in which intergranular flow is significant
High
Highly productive aquifers (not extensive)
Aquifers in which intergranular flow is significant
High
Highly productive aquifers (not extensive)
Aquifers in which flow is dominantly in fissures and other discontinuities
Moderate
Locally important aquifers
Aquifers in which intergranular flow is significant
Moderate
Locally important aquifers
Aquifers in which flow is dominantly in fissures and other discontinuities
Very low
Regions underlain by impermeable rocks, generally without groundwater except at shallow depth
Concealed aquifers, aquifers of limited potential, regions without significant groundwater
Mixed
Concealed aquifers; aquifers with limited or local potential
Concealed aquifers, aquifers of limited potential, regions without significant groundwater

Superficial Deposits

Proportions of the catchment covered by superficial deposits of generally high, generally low and mixed permeability based on classification of the BGS 1:625000 Superficial Deposits layer (version 4) as indicated in the table below. Superficial deposits generally have much more spatially variable permeability than bedrock. Superficial deposits vary greatly in their extent across the UK, some catchments having very extensive cover whilst others have negligible cover. Therefore, the percentages in each category do not sum to 100% in most catchments.

NRFA Superficial Deposits Permeability Class
BGS Lexicon Entry
Unmapped or Unsuitable
 
CRAG GROUP
Unmapped or Unsuitable
DRIFT GEOLOGY NOT MAPPED [FOR DIGITAL MAP USE ONLY]
Generally high permeability
BLOWN SAND
Generally high permeability
GLACIAL SAND AND GRAVEL
Generally high permeability
RAISED MARINE DEPOSITS (UNDIFFERENTIATED)
Generally high permeability
RIVER TERRACE DEPOSITS (UNDIFFERENTIATED)
Generally high permeability
SAND AND GRAVEL OF UNCERTAIN AGE AND ORIGIN
Generally high permeability
CLAY-WITH-FLINTS
Generally high permeability
LACUSTRINE DEPOSITS (UNDIFFERENTIATED)
Generally high permeability
PEAT
Mixed permeability
BRICKEARTH
Mixed permeability
TILL
Mixed permeability
ALLUVIUM
Mixed permeability
LANDSLIP