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The physical properties of major aquifers in England and Wales

By D.J. Allen, L.J. Brewerton, L.M. Coleby, B.R. Gibbs, M.A. Lewis, A.M. MacDonald, S.J. Wagstaff and A.T. Williams

Abstract

This report is the result of a three-year collaborative project\ud between the British Geological Survey and the National\ud Rivers Authority (now the Environment Agency). The\ud aim of the project has been to collect, collate and present\ud information concerning the physical hydraulic properties\ud of the major aquifers in England and Wales. The properties\ud addressed are those which are substantially invariant with\ud time; permeability and porosity, transmissivity and storage\ud coefficient. These properties have been investigated for the\ud six main aquifers; the Chalk, the Lower Greensand, the\ud Jurassic limestones, the Permo-Triassic sandstones, the\ud Magnesian Limestone and the Carboniferous Limestone.\ud Although the parameters studied were limited in number,\ud the study has proven to be both broad and complex for\ud several reasons. Firstly the aquifers themselves are\ud hydraulically complicated. They are in the main\ud heterogeneous, fractured\ud bodies of rock, sometimes with\ud indeterminate boundaries. This presents a double problem;\ud hydraulic tests on such materials often violate the classic\ud assumptions used in the test analysis, and the complexity\ud of the aquifers makes interpolation between data points\ud difficult. Secondly the physical properties of the aquifers\ud are often scale dependent, so that the value of a parameter\ud at one scale may not be appropriate for use at a larger or\ud smaller scale. Thirdly there are problems of data quality and\ud quantity. The quality of the pumping tests is variable and\ud many results are from pumping tests of short duration which\ud are designed more to assess the yields of boreholes than to\ud examine the properties of the aquifer. Also, data obtained\ud from boreholes tend to be clustered\ud in high yielding areas,\ud making an assessment of the true variation of hydraulic\ud properties across an aquifer difficult.\ud As a result of these difficulties the approach to the project\ud has been to collect both data and knowledge about the\ud aquifers, in order that the report can address not only the\ud magnitudes and variability of the aquifer parameters, but\ud also to provide some insight into factors controlling the\ud properties.\ud To this end project resources were used in two\ud distinct ways. Initially the main effort of the project was\ud put into data collection. This involved a detailed search\ud principally through the records of the former NRA, with\ud additional information from BGS, industry and published\ud and unpublished literature. Most of the data obtained were\ud from pumping tests, and these were digitised and stored\ud in a database designed for the project. The database was\ud linked with the BGS Core Analysis Database to form a\ud large set of basic data for the aquifers under consideration.\ud The second main strand of the project was the collection\ud of knowledge about the aquifers. This took the form both\ud of collecting reports of hydrogeological studies carried out\ud on the aquifers and of canvassing expert opinion (a vital\ud source of information which is not often published).\ud The results of these two approaches are synthesised in\ud this report. After the introductory sections each chapter\ud takes the form of a detailed review of the physical\ud properties of one aquifer (subdivided as necessary). The\ud purpose of the review is to present the magnitudes and\ud variability of the data (mainly from the database, but with\ud other examples) in the context of current understanding\ud of the controls\ud on the data. To that end the review\ud encompasses appropriate aspects of the geological,\ud geographical and physical hydrogeological nature of the\ud aquifers. Summaries of data from the database are also\ud presented in the form of appendices on an accompanying\ud CD-ROM.\ud The intention of the report is therefore not only to\ud acquaint the reader with the aquifer properties data values\ud which characterise the aquifers, but also to show the\ud perceived complexity of their hydraulic structure and the\ud physical controls on the data — there is therefore an overt\ud intention to dissuade the reader from taking raw values out\ud of context. A further purpose of the report is to provide a\ud comprehensive\ud set of references by which the reader can\ud obtain more detailed information about particular areas of\ud interest in an aquifer.\ud As a result of the collection and review of information\ud about the physical properties of the aquifers it is apparent\ud that there are many areas in which knowledge is inadequate.\ud For example the scale dependence of aquifer properties in\ud the Permo-Triassic sandstones, and in particular the effects\ud of fractures, are perceived to be important but are poorly\ud understood. In the Chalk the extent to which the aquifer\ud may be considered to be karstic, in the sense of allowing\ud rapid flow to occur in discrete zones of high permeability,\ud is an often debated issue on which there has been little\ud research. Many other areas of uncertainty are apparent in\ud the information presented in this report; however\ud this is\ud an important function of the study, for by summarising the\ud extent of available knowledge its inadequacies will be more\ud readily seen

Publisher: British Geological Survey
Year: 1997
OAI identifier: oai:nora.nerc.ac.uk:13137

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  1. (1993). 10 m below top Chalk 10 –30 m below top Chalk >30 m below top Chalk Sy Ss (m -1 ) Sy Ss (m -1 ) Sy Ss (m -1 ) RWL above top of
  2. 15 Cumulative Frequency (%)
  3. (1973). 99 Figure 4.2.19 Geophysical logging at Chitterne; fractures are present to a depth of 100 m but 90% of the flow comes from above 47 m, with the most productive fractures above 35 m (after Avon and Dorset River Authority,
  4. (1981). A cave system has been identified and examined within the Chalk at Beachy Head (Reeve,
  5. (1976). A conceptual model of how transmissivity is developed within the Chalk has been suggested for the Kennet
  6. (1992). A groundwater model was also constructed for Wallop Brook, a tributary catchment of the River Test (Mott MacDonald,
  7. (1972). A method of calculating storage from recession curves has been applied to the Chalk, the results of which are of wide spread importance to the estimation of storage through out the Chalk (Headworth,
  8. (1993). A model has recently been developed for the Alre and Cheriton catchments (Irving,
  9. (1979). A series of springs issue from the foot of the Chalk escarp ment. Their location is largely controlled by the under lying geology and therefore gives some information on the hydraulic properties of the various units within the Chalk (Morel,
  10. (1974). A similar scenario was observed at the Havant and Bedhampton springs in Hampshire where tracer tests indicated flow velocities of 2 km/d
  11. (1984). A statistical study of specific capacities of boreholes in the Chalk of East Anglia and their use in predicting borehole yields.
  12. (1986). A statistical study of specific capacities of boreholes in the Sherwood Sandstone Group around Birmingham and Wolverhampton.
  13. (1974). An extensive adit system was built within the Chalk aquifer during the second half of the nineteenth century and early part of the twentieth century (Mustchin,
  14. (1991). Applied Groundwater Modelling.
  15. (1993). As part of a project calculating the volume of groundwater stored in the Chalk aquifer, BGS
  16. (1992). As part of an investigation into the effects of groundwater abstraction on river flows a numerical model was made covering the whole of the Salisbury Plain (Halcrow,
  17. (1978). b) Gradual increase in drawdown (Figure 4.1.18b) A gradual increase in drawdown is often observed if a pumping test borehole is located within a
  18. (1992). Boreholes within the Chalk of the South Downs have been pumping sand (Southern Science,
  19. (1987). Comparison of geostatistical methods for estimating transmissivity using data on transmissivity and specific capacity.
  20. (1994). consistent with geological literature (see Bloomfield,
  21. (1978). d ) 0. 01 0. 02 0. 03 97 96 95 94 S t o r a g e C o e f f i c i e n t 97
  22. (1991). Data from the Chilgrove Borehole in the South Downs (Institute of Hydrology/British Geological Survey,
  23. (1972). deposited in East Anglia by the Anglian glaciation confines the Chalk in places, restricting the circulation of groundwater (Bonell,
  24. (1994). Different water levels are recorded in boreholes in close proximity. Pumping can have a very rapid effect on water levels in a borehole or spring several kilometres away from the pumping borehole, for example Swanbourne Lake, South Downs (Southern Science,
  25. (1986). During the Anglian glaciation the geomorphology of East Anglia was modified significantly, changing the landscape from a series of north-east sloping river terraces to a glacial terrain composed of till with a radial drainage pattern (Bowen et al.,
  26. (1973). Eocene deposits are found on many of the interfluves in the south-east of the area (Figure 4.1.15). Clay-withflints deposits are common on the summits of the Upper Chalk ridges, but are also found further down the slopes (Jarvis,
  27. (1974). Extensive adit systems were built in different parts of the Chalk aquifer during the second half of the 19th and early part of the 20th century (e.g. Mustchin,
  28. (1983). Figure 4.1.11 The density of solution features on the outcrop of the Chalk per 100 km 2 (after Edmonds,
  29. (1993). Figure 4.1.12 Characteristic patterns of winterbourne recession observed in the southern Chalk — the shaded area indicates flow (data from NRA, Southwest Region,
  30. (1992). Figure 4.1.3 The limits of the Anglian and Devensian ice sheets in southern Britain (after Boulton,
  31. (1972). Figure 4.1.8 Correlation between matrix porosity and horizontal hydaulic conductivity for samples from the Chalk. Porosity (%)
  32. (1977). Figure 4.2.10 The distribution of solution features in the Chalk of the Dorset Heathlands, illustrating the association with the younger strata (after Sperling
  33. (1989). Figure 4.3.10 Vertical distribution of transmissivity used in a transient groundwater flow model of the Kennet Valley (after
  34. (1986). Flint occurs predominately in layers parallel to bedding, either in tabular layers or as scattered discrete nodules
  35. (1958). Geomorphological evidence of karst characteristics are wide spread
  36. (1993). H y draulic Conductivit y (m/d)
  37. (1968). Harder nodular chalks, referred to as hardgrounds or Grade I chalks
  38. (1989). Hydraulic continuity between the Chalk and the Upper Greensand is thought to be limited over much of the Kennet Valley due to the clayey nature of the Lower Chalk. An exception to this is around Woodsend (Rushton et al.,
  39. (1978). In addition to the logging evidence, pumping tests also implied the importance of shallow fractures (Connorton and Reed,
  40. (1982). In parallel with the river augmentation project, the Institute of Geological Sciences (now BGS) carried out permeability tests using a variety of different techniques (Price et al., 1977; Price et al.,
  41. (1981). Laboratory work has illustrated that highly folded chalk has lower porosity and intergranular permeability than undisturbed chalk (Alexander,
  42. (1968). Many authors have illustrated that classical pumping test analysis is possible in fractured rocks subject to several basic conditions (e.g. Snow,
  43. median of 0.0018 and 0.0022 respectively. The 25 percentile is 6.1
  44. (1985). Modelling of the aquifer system reinforces the nonlinear vertical distribution of transmissivity
  45. (1992). modelling work undertaken in the Wallop Brook catchment included discussions of vertical variations in permeability (Mott MacDonald,
  46. (1993). Packer testing in the Chichester Block at three inland locations showed that the aquifer properties were best devel oped within about 40 m of the water table (NRA Southern Region,
  47. (1989). remain open at greater depths than softer chalk. The open fractures allow groundwater to flow through them generating preferential flow paths which may then be enhanced by dissolution.
  48. (1989). S i n g l e d e e p f a s t - f l o w i n g C h a n n e l S h a l l o w A n a b r a n c h C h a n n e l s
  49. (1992). Several factors could account for the high degree of solu tion activity associated with cover: 1. Soils associated with Palaeogene deposits and clay-withflints tend to be quite acidic (Edmunds et al.,
  50. (1990). Solifluction deposits are extensive on the Chalk of southern England and are shown on Geological Survey 22 Outcro p of Chal k Palaeo g ene river s
  51. (1983). Solution pipes and swallow holes are also observed in the South Downs and can have an important effect on the aquifer properties of the Chalk (Mortimore et al., 1990; Edmonds,
  52. (1981). Specific Capacity (m /d/m
  53. (1975). specific yield; Ss = specific storage; RWL = rest water level in Spring
  54. specific yield; Ss = specific storage; RWL = rest water level in Spring 1975. <10 m below top Chalk 10 –30 m below top Chalk >30 m below top Chalk Sy Ss (m -1 ) Sy Ss (m -1 ) Sy Ss (m -1 ) RWL above top of Chalk 0.5
  55. (1976). Speleologists have long recognised and explored the karstic nature of the Chalk (e.g. Reeve,
  56. (1994). Such an event occurred in Chichester during
  57. (1976). sug gested that the matrix was relatively unimportant for storage within the Yorkshire Chalk.
  58. (1993). Tectonic history of the Chalk In north-west Europe the Chalk was deposited in three tectonic settings: (1) above and against massifs of Palaeozoic and older rocks; (2) in basins between massifs; and (3) in fault-bounded troughs within basins (Hancock,
  59. (1974). testing on an interfluve in the Chichester block gave a transmissivity value of only 1 m 2 /d while pumping tests in the Winterbourne valley at Houndean Farm [TQ 397 098] indicated transmissivity values of >1000 m 2 /d (Sussex River Authority,
  60. (1978). The Chalk Group of the northern province was divided on lithological grounds into four formations in Yorkshire and Humberside by Wood and Smith
  61. (1987). The Chalk is often referred to as possessing dual porosity (Price,
  62. (1990). The common methods of pumping test analysis used on Chalk boreholes
  63. (1975). The detailed investigations of the Itchen augmentation scheme have given further information on the variation of aquifer properties with depth. From individual pumping tests carried out at different rest water levels
  64. (1975). The distribution of aquifer properties is slightly complicated by the presence of the low permeability Chalk Marl towards the base of the Lower Chalk (Robins
  65. (1988). The effective thickness of the Upper Greensand aquifer is generally 20 –30 m and the hydraulic conductivity approximately 1 m/d (Shaw and Packman,
  66. (1988). The more esoteric nature of the aquifer has been investigated as part of a tracer experiment near
  67. (1989). The role of three-dimensional geographic information systems in subsurface characterization for hydrogeologic applications.
  68. (1992). The uppermost Flamborough Chalk Formation consists of well-bedded flintless chalk with stylolitic surfaces and marl partings
  69. (1990). There are many groundwater mounds throughout Hampshire. These mounds are generally located on the axes of anticlines for example at Ellisfield, Lasham, Medstead and Preshaw in east Hampshire (Giles and Lowings,
  70. (1974). there is evidence that rapid groundwater flow is more likely near to the Eocene cover
  71. (1989). There is little field evidence to describe the vertical distribution of the aquifer properties high up on the interfluves. The recent groundwater model, however, requires the same non-linear behaviour as is observed in the valleys (Rushton et al.,
  72. (1993). There is some evidence that chalks are not simply the result of a gentle accumulation of debris. In some areas resedi mentation has taken place in the form of slide sheets, slump deposits, turbidites, debris flows and laminated chalks
  73. (1978). Thirty-three abstraction boreholes were drilled as part of the scheme. Each of these was subjected to numerous tests and the aquifer response measured using purpose built observation boreholes (Owen et al.,
  74. (1973). This horizon is well cemented and has low permeability. The Chalk Marl at the base of the Lower Chalk has low permeability
  75. (1996). Three basic types of fracture can be recognised in the Chalk, faults, bedding plane fractures and joints
  76. (1960). Throughout most of the outcrop of the Kennet Valley the Chalk dips gently to the south-east and passes under Eocene deposits. The total thickness of the Chalk is prob ably about 220 m (Institute of Geological Sciences,
  77. (1993). Two principal periods of tectonic activity affected the Chalk. The first, in Late Cretaceous time influenced the deposition and the second, during early Oligocene to early Miocene time led to gentle folding and faulting
  78. (1979). Upper Chalk underlies most of Hampshire (Figure 4.2.22). At outcrop it is commonly 80 – 150 m thick but can be as thick as 400 m where uneroded and confined by Palaeogene deposits (Institute of Geological Sciences and Southern Water Authority,
  79. with horizontal adits extending laterally for up to 1000 m. In Victorian times the drilling rig superseded the well diggers, allowing exploitation to increase rapidly. Within the London Basin itself the Chalk is confined by Palaeo gene deposits.

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