Searches User Guide: Hydrogeology & hydrology

Superficial hydrogeology

Aquifers within Superficial aquifer

Provides details of aquifer status of groundwater held within superficial geology. The data is based on 1:50,000 scale geology.

The aquifer maps display the following aquifer designations:

Aquifer designation	Description
Principal	These are layers of rock or drift deposits that have high intergranular and/or fracture permeability - meaning they usually provide a high level of water storage. They may support water supply and/or river base flow on a strategic scale. In most cases, principal aquifers are aquifers previously designated as major aquifer.
Secondary A	Permeable layers capable of supporting water supplies at a local rather than strategic scale, and in some cases forming an important source of base flow to rivers. These are generally aquifers formerly classified as minor aquifers.
Secondary B	Predominantly lower permeability layers which may store and yield limited amounts of groundwater due to localised features such as fissures, thin permeable horizons and weathering. These are generally the water-bearing parts of the former non-aquifers.
Secondary undifferentiated	Has been assigned in cases where it has not been possible to attribute either category A or B to a rock type. In most cases, this means that the layer in question has previously been designated as both minor and non-aquifer in different locations due to the variable characteristics of the rock type.
Unproductive strata	These are rock layers or drift deposits with low permeability that have negligible significance for water supply or river base flow.

Data source: British Geological Survey, the Environment Agency and Natural Resources Wales
Data update schedule: Quarterly

Superficial geology

Superficial geological deposits at 1:50,000 scale. Superficial deposits (formerly known as ‘drift’ by the BGS) are the youngest geological deposits formed during the most recent period of geological time, the Quaternary, which extends back about 2.6 million years from the present.

Data source: British Geological Survey
Data update schedule: Quarterly

Bedrock hydrogeology

Aquifers within bedrock geology

Provides details of aquifer status of groundwater held within bedrock geology. The data is based on 1:50,000 scale geology.

The aquifer maps display the following aquifer designations:

Aquifer designation	Description
Principal	These are layers of rock or drift deposits that have high intergranular and/or fracture permeability - meaning they usually provide a high level of water storage. They may support water supply and/or river base flow on a strategic scale. In most cases, principal aquifers are aquifers previously designated as major aquifer.
Secondary A	Permeable layers capable of supporting water supplies at a local rather than strategic scale, and in some cases forming an important source of base flow to rivers. These are generally aquifers formerly classified as minor aquifers.
Secondary B	Predominantly lower permeability layers which may store and yield limited amounts of groundwater due to localised features such as fissures, thin permeable horizons and weathering. These are generally the water-bearing parts of the former non-aquifers.
Secondary undifferentiated	Has been assigned in cases where it has not been possible to attribute either category A or B to a rock type. In most cases, this means that the layer in question has previously been designated as both minor and non-aquifer in different locations due to the variable characteristics of the rock type.
Unproductive strata	These are rock layers or drift deposits with low permeability that have negligible significance for water supply or river base flow.

Data source: British Geological Survey, Environment Agency and Natural Resources Wales
Data update schedule: Quarterly

Groundwater abstraction licences

These are records of licences for groundwater abstractions from the aquifers in the area. Abstractions of groundwater can be for uses such as an industrial process that requires large amounts of water, irrigation and drinking water. For national security purposes, the locational accuracy of some abstraction licences may be degraded.

Data source: Environment Agency and Natural Resources Wales
Data update schedule: Quarterly

Bedrock geology

Bedrock geology at 1:50,000 scale. Bedrock geology (formerly known as ‘solid’ geology by the BGS) is a term used for the main mass of rocks forming the Earth and present everywhere, whether exposed at the surface in outcrops or concealed beneath superficial deposits or water. The bedrock has formed over vast lengths of geological time ranging from ancient and highly altered rocks of the Proterozoic, some 2500 million years ago, or older, up to the relatively young Pliocene, 2.6 million years ago.

Data source: British Geological Survey
Data update schedule: Quarterly

Source protection zones and drinking water abstractions

Source protection zones

Source Protection Zones (SPZs) define the sensitivity of an area around a potable abstraction site to contamination.

The purpose of SPZs is to provide additional protection to safeguard drinking water quality through constraining the proximity of an activity that may impact upon a drinking water abstraction.

Zones around location sites are defined by groundwater travel time to an abstraction. This is determined through applying Environment Agency groundwater flow models run at the location of abstractions, inputting parameters such as flow direction, geology type, rainfall and hydrological boundaries.

The SPZ maps are produced at 1:50,000 scale.

SPZ type	Description
Zone 1 (inner protection zone)	This zone is defined by a travel time of 50 days or less from any point within the zone at, or below, the water table. Additionally, the zone has a minimum of a 50m radius. It is based principally on biological decay criteria and is designed to protect against the transmission of toxic chemicals and water-borne disease. In geological settings where a confining layer is present, this is indicated as Zone 1c.
Zone 2 (outer protection zone)	This zone is defined by the 400 day travel time from a point below the water table. Additionally this zone has a minimum radius of 250 or 500m, depending on the size of the abstraction. The travel time is derived from consideration of the minimum time required to provide delay, dilution and attenuation of slowly degrading pollutants. In geological settings where a confining layer is present, this is indicated as Zone 2c.
Zone 3 (total catchment)	This zone is defined as the total area needed to support the abstraction or discharge from the protected groundwater source. In geological settings where a confining layer is present, this is indicated as Zone 3c.
Zone 4 (zone of special interest)	Zone of special interest was previously defined for some groundwater sources. These zones highlighted areas (mainly on non-aquifers) where known local conditions meant that potentially polluting activities could impact on a groundwater source even though the area is outside the normal catchment of that source. In future this zone will be incorporated into one of the other zones (1, 2 or 3) whichever is appropriate in the particular case.

Data source: Environment Agency and Natural Resources Wales
Data update schedule: Quarterly

Source protection zones in confined aquifer

Source Protection Zones in the confined aquifer define the sensitivity around a deep groundwater abstraction to contamination. A confined aquifer would normally be protected from contamination by overlying geology and is only considered a sensitive resource if deep excavation/drilling is taking place.

Please refer to the table presented above for full descriptions of SPZ type.

Data source: Environment Agency and Natural Resources Wales
Data update schedule: Quarterly

Drinking water abstraction licences

These are records of licences for groundwater abstractions for drinking water. For national security purposes, the locational accuracy of some abstraction licences may be degraded.

Data source: Environment Agency and Natural Resources Wales
Data update schedule: Quarterly

Hydrology

Water courses from Ordnance Survey

Detailed water network data showing the flow and precise course of every river, stream, lake and canal. This dataset provides a detailed centre line following the curve of the waterway precisely.

Data source: Ordnance Survey
Data update schedule: Quarterly

Surface water abstractions

These are records of licences for water abstractions from the surface water features in the area. Abstractions of surface water can be for uses such as an industrial process that requires large amounts of water, irrigation and in some cases for drinking water. For national security purposes, the locational accuracy of some abstraction licences may be degraded.

Data source: Environment Agency and Natural Resources Wales
Data update schedule: Quarterly