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.
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 Geology layer (version 5) 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 |
|---|---|
High | Highly productive fissured aquifers |
| High | Highly productive aquifers with intergranular flow |
Moderate | Locally important fissured aquifers |
| Moderate | Locally important aquifers with intergranular flow |
Very low | Areas underlain by impermeable rocks, generally without groundwater except at shallow depth |
Mixed | Concealed aquifers; aquifers with limited or local potential |
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 5) 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 |
|---|---|
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 low permeability | CLAY-WITH-FLINTS |
Generally low permeability | LACUSTRINE DEPOSITS (UNDIFFERENTIATED) |
Generally low permeability | PEAT |
Mixed permeability | BRICKEARTH |
Mixed permeability | TILL |
Mixed permeability | ALLUVIUM |
Mixed permeability | LANDSLIP |
