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The puzzle of high heads beneath the West Cumbrian coast, UK: a possible solution

The puzzle of high heads beneath the West Cumbrian coast, UK: a possible solution
The puzzle of high heads beneath the West Cumbrian coast, UK: a possible solution
A region of high heads within the Borrowdale Volcanic Group (BVG; a fractured crystalline rock) beneath the coastal plain of West Cumbria, England (UK), is identified as a possible relic left over by the Late Devensian ice sheet. It was found during investigations in the 1990s. Contemporary modelling work failed to produce a satisfactory explanation of the high heads compatible with the ‘cold recharge’ isotopic signature of the groundwater. This study has reassessed the original hydraulic testing results. By plotting density-adjusted heads versus their depth below the water table in the immediate vicinity of the borehole in which they were measured, a depth profile resembling a ‘wave’ was revealed with a peak value located at 1,100 m depth. The possibility that this wave represents relic heads from the last major ice sheet has been assessed using one-dimensional mathematical analysis based on a poroelastic approach. It is found that a wet-based ice sheet above the West Cumbrian coast was probably thick enough and sufficiently long-lasting to leave such relic heads providing that the hydraulic diffusivity of the BVG is in the order of 10?6 m s?1. Initial assessment 20 years ago of the long-interval slug tests suggested that such low values are not likely. More recent interpretation argues for such low values of hydraulic diffusivity. It is concluded that ice sheet recharge is the most likely cause of the raised heads, that the BVG contains significant patches of very low conductivity rock, and that long-interval single-hole tests should be avoided in fractured crystalline rock.
1431-2174
439-457
Black, J.H.
4ce17ff5-6851-4504-99fa-5bc3909bc292
Barker, J.A.
33bf9dec-cc9b-451c-8192-46099e316b6d
Black, J.H.
4ce17ff5-6851-4504-99fa-5bc3909bc292
Barker, J.A.
33bf9dec-cc9b-451c-8192-46099e316b6d

Black, J.H. and Barker, J.A. (2016) The puzzle of high heads beneath the West Cumbrian coast, UK: a possible solution. Hydrogeology Journal, 24 (2), 439-457. (doi:10.1007/s10040-015-1340-4).

Record type: Article

Abstract

A region of high heads within the Borrowdale Volcanic Group (BVG; a fractured crystalline rock) beneath the coastal plain of West Cumbria, England (UK), is identified as a possible relic left over by the Late Devensian ice sheet. It was found during investigations in the 1990s. Contemporary modelling work failed to produce a satisfactory explanation of the high heads compatible with the ‘cold recharge’ isotopic signature of the groundwater. This study has reassessed the original hydraulic testing results. By plotting density-adjusted heads versus their depth below the water table in the immediate vicinity of the borehole in which they were measured, a depth profile resembling a ‘wave’ was revealed with a peak value located at 1,100 m depth. The possibility that this wave represents relic heads from the last major ice sheet has been assessed using one-dimensional mathematical analysis based on a poroelastic approach. It is found that a wet-based ice sheet above the West Cumbrian coast was probably thick enough and sufficiently long-lasting to leave such relic heads providing that the hydraulic diffusivity of the BVG is in the order of 10?6 m s?1. Initial assessment 20 years ago of the long-interval slug tests suggested that such low values are not likely. More recent interpretation argues for such low values of hydraulic diffusivity. It is concluded that ice sheet recharge is the most likely cause of the raised heads, that the BVG contains significant patches of very low conductivity rock, and that long-interval single-hole tests should be avoided in fractured crystalline rock.

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More information

Accepted/In Press date: 2 November 2015
e-pub ahead of print date: 1 December 2015
Published date: March 2016
Organisations: Infrastructure Group

Identifiers

Local EPrints ID: 397677
URI: https://eprints.soton.ac.uk/id/eprint/397677
ISSN: 1431-2174
PURE UUID: 2cf5532b-f247-4286-985a-33491eae19ad

Catalogue record

Date deposited: 05 Jul 2016 08:54
Last modified: 15 Jul 2019 20:18

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