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A strategic programme for NERC Lowland catchment research
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Towards a methodology for determining the pattern and magnitude of recharge through drift deposits

Title

Recharge through drift.

Overview of project

This project's goal has been to improve the current understanding of the relationship between glacial drift structure and recharge, for groundwater sustainability and vulnerability assessments. Researchers gatherd data to describe the physical and hydraulic conditions at different scales of measurement. Identifying and comparing alternative strategies to aquire data was as important as gathering data itself. This project improved the description of the processes governing recharge and enhanced our understanding of the pathways and rates of migration through the shallow subsurface.

Aims

The primary objective was to gain greater insight into the hydraulic properties and processes of the main glacial formations overlying the Permo-Triassic sandstone aquifer that control the patterns and magnitudes of recharge to the underlying aquifer. A related and key objective was to seek a general method for estimating recharge patterns through drift based on the identification of an appropriate strategy for the collection of field measurements at the catchment scale.

Main findings

The lodgement till hydraulic properties are significantly controlled by vertical desiccation cracks that permit significant rapid vertical flow through the otherwise low permeability tills.

The spacing and depth of the desiccation cracks are highly organised, indicating that they were generated concurrently. They are essentially uniform over the region, therefore, estimates of recharge do not require extensive mapping of these features.

While the till hydraulic properties would suggest that there is little recharge taking place through the tills, lateral flows above the tills to the till edge and subsequent recharge by deep infiltration along the till edge provides significant enhancement of the overall recharge from the tills.

Previous mapping identifies the correct overall area of the tills but does not delineate adequately either the shapes of the till bodies, the depth to the top of the till upper surface or the length and position of the till edges. These are the significant properties of the till structure governing the determination of enhanced recharge.

The distribution of the lodgement tills can be identified using geophysical methods with some ground truth data. Two dimensional surveying of resistivity provided the most reliable data on geometry of the drift formations during the project.

Project outputs

  • Improved glacial drift mapping and characterisation to enable estimation of recharge using a combination of low density surface geophysics and targeted sampling methods.
  • Completion of a 3D conceptual hydrogeological model of the glacial deposits spanning all field scales from local to catchment. The model is quantified using geostatistical simulation approaches to investigate both the magnitude and timing of recharge and the uncertainty in its estimation.
  • Experimental studies of the small-scale flow patterns and recharge rates at two sites have demonstrated the importance of two new elements of the conceptual hydraulic model for the low permeability lodgement tills:
    • the impact of the self-organised dessication cracks observed in the till to depths of more than six metres; and
    • the depth to the upper till surface and the proximity of the till edge that govern the lateral transport of water to the underlying Sandstone aquifer.

Areas of application

The primary application areas for the research are climate change prediction, contaminated land and pollutant risk assessment, and performance assessment for the geological disposal of nuclear waste. Those organisations with requirements for the knowledge gained from this study will be primarily involved in environmental decision making and risk assessment.

Future climate change will need to address the long-term changes to the available resources, including groundwater. Understanding future changes to the long-term recharge rate, depends on a good description of the processes governing recharge. The issues of contaminated land and the fate and transport of pollutants from contamination require a good understanding of the pathways and rates of migration through the shallow subsurface. Finally, the nuclear waste industry requires assessments of the risk to the biosphere from radionuclide releases. Understanding the impact of shallow ground conditions on the transmission of radionuclides beneath the soil zone forms an important contribution to such assessments.

Researchers' details

Principal Investigator:

Co-investigators:

Researcher:

Publications

All publications from this and other LOCAR projects are listed in the publications database.

Refereed Journal Papers

Cuthbert M O, Mackay R, & Tellam J H, submitted 2008. The use of electrical resistivity tomography in deriving local scale models of recharge through superficial deposits, Quarterly Journal of Engineering Geology and Hydrogeology.

Mackay R, Cuthbert M O, Ash H & Tellam J H, 2006. Numerical upscaling to quantify aquifer recharge through glacial drift deposits, Shropshire, UK. In Bierkens, M. F. P., Gejrels, J. C., and KOvar, K. (eds) Calibration and reliability in groundwater modelling: from uncertainty to decision making, IAHS Publication 304, 52-57.

PhD theses

Cuthbert M O 2006. Hydraulic processes controlling recharge through glacial drift. Unpublished PhD Thesis, University of Birmingham.

Thatcher K E (due submission May 2008). Hydraulic and Geostatistical Modelling of Glacial Drift to determine groundwater recharge in the Tern Catchment , Unpublished PhD thesis, University of Birmingham.

MSc theses

Garrick H 2003. The Impact of Groundwater Abstraction on the Potford and Platt Surface Water Catchment, Tern Catchment, Shropshire. MSc Thesis, Earth Sciences, University of Birmingham.

Luck J 2003. Investigation of the relationships between borehole resistivity, colour and hydraulic properties of Glacial Tills in the Tern Catchment. . MSc Thesis, Earth Sciences, University of Birmingham.

Refereed conference and discussion papers

Cuthbert M O, Russell E J F, Barker, R D & Mackay, R 2004. The effect of seasonal temperature variations on the resistivity of glacial till. Proceedings of 10th Annual Meeting of Environmental and Engineering Geophysics, Utrecht, P032, 1-4. (ISBN 90-73781-37-X)

Cuthbert M O, Mackay, R, Tellam J H. and Humpage, A J 2004. Local and regional scale controls on recharge in a drift covered catchment. In Groundwater Flow Understanding: from local to regional scales, Proceedings of XXXIII IAH Congress and 7th ALHSUD Congress, Zacatecas, Mexico, T5-13, 1-4. (ISBN 970-32-1749-4)

Mackay R, Cuthbert M O, Ash H & Tellam J H, 2005. Towards an up-scaled model of aquifer recharge through glacial drift deposits, Shropshire, UK. Model Care 2005 Conference Proceedings, The Hague, The Netherlands.

Conference abstracts

Cuthbert M O, Mackay, R, Lawrence, A R & Peach D 2003. Understanding regional and local scale hydraulic processes controlling recharge through drift. Geophysical Research Abstracts Volume 5, EGS-AGU-EUG Joint Assembly 2003, EAE03-A-12910.

Cuthbert M O, Mackay, R, & Barker R D 2004. The use of electrical resistivity tomography (ERT) in deriving recharge models for a drift covered catchment. Geophysical Research Abstracts Volume 6, EGU General Assembly 2004, EGU04-A-05080.

Thatcher K E, Mackay, R, & Priestly A 2006. Modelling unsaturated flow through heterogeneous drift using ECLIPSE. Geophysical Research Abstracts Volume 8 EGU06-A-06039Poster presented at EGU General Assembly, April 2006 .

Thatcher K E & Mackay, R 2006. Assessing uncertainty in recharge estimates through glacial drift. Geophysical Research Abstracts Volume 8, EGU06-A-06009.Poster presented at EGU General Assembly, April 2006

Thatcher K E & Mackay, R 2007. Combining Electrical Techniques to map a Till Aquitard for Quantifying Lateral Flows and Improved Recharge Estimation, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract H42B-05; Paper presented at the AGU Fall Meeting, San Francisco , December 2007.

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