The Chalk Aquifer of the North Downs
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The Chalk aquifer of the North Downs Research Report RR/08/02 BRITISH GEOLOGICAL SURVEY The National Grid and other Ordnance Survey data are used with the permission of the RESEARCH REPORT RR/08/02 Controller of Her Majesty’s Stationery Office. Licence No: 100017897/2008. Key words Hydrogeology, Chalk, hydro- chemistry, groundwater management, North Downs. Front cover View south-east from the Middle The Chalk aquifer of the Chalk of the North Downs scarp face at Albury Downs, Surrey (P212885). North Downs Bibliographic reference AD A MS , B (editor). 2008. 1 The Chalk aquifer of the B Adams (editor) North Downs. British Geological Survey Research Report, RR/08/02. 60pp. Contributors Your use of any information 2 1 1 1 1 provided by the British K Baxter, D Buckley, J Cunningham, P Hopson, B Ó Dochartaigh, Geological Survey (BGS) is at M Packman,3 V Robinson,4 R Sage,5 P Smedley,1 P Shaw,6 P Waring,7 your own risk. Neither BGS nor G Warren,7 S Watson8 the Natural Environment Research Council gives any warranty, condition or representation as to the quality, accuracy or completeness of the information or its suitability for any use or purpose. All implied conditions relating to the quality or suitability of the information, 1 2 3 4 British Geological Survey, Thames Water, Southern Water, (formerly) and all liabilities arising from the 5 6 supply of the information Environment Agency (Thames Region), Veolia Water, Environment Agency (including any liability arising in (Southern Region), 7 (formerly) Environment Agency (Southern Region), negligence) are excluded to the 8 fullest extent permitted by law. (formerly) University College London Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail [email protected]. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract. Maps and diagrams in this book use topography based on Ordnance Survey mapping. Some features of figures 1.1, 1.3, 1.4, 1.5 and 1.6 are based on spatial data licensed from the Centre for Ecology and Hydrology. ISBN 978 0 85272 571 9 © NERC 2008. All rights reserved. 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It also undertakes programmes of technical aid in geology in developing countries. Columbus House, Greenmeadow Springs, Tongwynlais, Cardiff CF15 7NE The British Geological Survey is a component body of the Tel 029 2052 1962 Fax 029 2052 1963 Natural Environment Research Council. Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB Tel 01491 838800 Fax 01491 692345 Geological Survey of Northern Ireland, Colby House, Stranmillis Court, Belfast BT9 5BF Tel 028 9038 8462 Fax 028 9038 8461 www.bgs.ac.uk/gsni/ Parent Body Natural Environment Research Council, Polaris House, North Star Avenue, Swindon, Wiltshire SN2 1EU Tel 01793 411500 Fax 01793 411501 www.nerc.ac.uk Website: www.bgs.ac.uk Shop online at: www.geologyshop.com Preface This report is a product of the National Groundwater available knowledge. Members of the advisory panel Survey (NGS), a component part of the British also contributed much valuable information and acted as Geological Survey’s (BGS) Groundwater Management reviewers. Thus, this report brings together information Programme. The NGS aims to provide strategic scientific from published and unpublished sources written by, and underpinning for groundwater resources management reviewed by hydrogeologists with extensive experience and protection. The survey is carried out through studies of development and management of the aquifer, from of major aquifer blocks, which focus on describing and quantity, quality and groundwater protection perspectives. quantifying the occurrence of groundwater in British The editor also acknowledges the reviews and comments aquifers, its movement and natural quality as well as the of other Environment Agency staff which provided processes controlling solute and contaminant transport updates on several of the models and management projects and degradation. These descriptions are based on review discussed in this report. It therefore aims to summarise the of existing knowledge and data, supported by collection current understanding of the hydrogeology of the Chalk and interpretation of new data as well as undertaking aquifer of the North Downs and provide a foundation on relevant research of generic or regional significance. which further work can be based. Advisory panels at both the national and regional levels The report is in a series providing comprehensive have been established to ensure that the development of descriptions of major blocks of the Chalk aquifer in the UK. the programme, within the overall objectives, reflects the The relevance of this work has been brought into sharper needs of the user community. focus recently by the need to characterise groundwater This study of the Chalk aquifer of the North Downs bodies in order to meet the requirements of the European was carried out in collaboration with Environment Water Framework Directive. In addition the series will Agency (Thames and Southern Regions), Southern Water, provide a starting point for improving our understanding Thames Water, Mid Kent Water, Folkestone and Dover of this and other blocks of aquifer as changing Water Services and Sutton and East Surrey Water. An demands are made on resources, storage capacity and advisory panel involving members of these organisations environmental needs in response to societal and climatic ensured that the work is relevant and is based on best change. iii Acknowledgements This study could not have been completed without the active cooperation of the Project Advisory Board, which comprised the following: K Baxter (Thames Water) M Packman (Southern Water) V Robinson (formerly Environment Agency) R Sage (Veolia Water) P Shaw (Environment Agency) P Waring (Environment Agency) G Warren (formerly Environment Agency) S Watson (University College London) Typesetting was prepared by Pauline Sapey. Illustrations were prepared by Pauline Sapey and Paul Lappage. iv Contents Preface iii 2.1 Stratigraphy of the Chalk of southern England 7 2.2 Lithofacies within the Thanet Sand Formation and Acknowledgements iv Lambeth Group (after Ellison, 1983) 8 2.3 Schematic cross-section showing the relationship Executive summary vii between the Palaeogene, Neogene and clay-with- flints in east and west Kent 10 1 Introduction 1 2.4 Small-scale structures within the Chalk and 1.1 Location and description of the North Palaeogene (after Wooldridge and Linton, 1955; Downs 1 and Lake, 1975) 11 1.2 Topography and geomorphology 1 3.1 Hydrogeological sections across the North Downs 1.3 Climate 3 (after Day et al., 1970) 13 1.4 Drainage 3 3.2 The limits of the Anglian and Devensian ice 1.5 Land use 4 sheets in southern Britain (after Boulton, 1992) 14 2 Geology and structure 5 3.3 Dry valley occurrence in the Dover–Deal 2.1 Introduction 5 area 19 2.2 Geological sequence in the North Downs 5 3.4 The density of solution features on the outcrop of 2.3 Structural setting 10 the Chalk per 100 km2 (after Edmonds, 1983) 21 3.5 Groundwater level hydrographs for three 3 Hydrogeology 13 observation wells in the North Downs Chalk 22 3.1 The Chalk aquifer of the North Downs 13 3.6 Typical resistivity log profiles for the Chalk from 3.2 Evolution of the Chalk aquifer of the North the South Downs and the North Downs, from Downs 14 south to north 24 3.3 The unsaturated zone, recharge and influence 3.7 Composite plot of geophysical logs from the of overlying deposits 15 Reculver Borehole 1 25 3.4 The saturated zone 18 3.8 Geological structure and fluid entry levels 3.5 Lithological and structural control on identified from geophysical logs, north Kent 26 groundwater flow 22 3.9 Fluid logs of selected boreholes adjacent to the 3.6 The regional water balances 27 Thames estuary 27 3.7 A conceptual model of groundwater circulation 3.10 Buried channels offshore of north Kent (after in the Chalk 30 Bridgland and d’Olier, 1995) 28 3.11 Generalised potentiometric