BGS karst report series : J3. Karst in the Jurassic Great and Inferior Oolite Groups of southern England

Maurice, L.D.; Farrant, A.R.; Mathewson, E.. 2023 BGS karst report series : J3. Karst in the Jurassic Great and Inferior Oolite Groups of southern England. Nottingham, UK, British Geological Survey, 71pp. (OR/23/002) (Unpublished)

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This report documents the evidence for karst and rapid groundwater flow in the Great and Inferior Oolite group aquifers of southern England. It is part of the BGS karst report series on those karst aquifers in England in which cave development is limited – principally the Upper Cretaceous Chalk and the Jurassic and Permian limestones. The term “karst” applies to rocks that are soluble. In classic karst there are extensive caves and large-scale surface karst landforms such as dolines, shafts, stream/river sinks, and springs. In the past, the Chalk and the Jurassic and Permian limestones of England were not considered karstic because they have limited cave development, and because karst features are usually small and have not been well documented. These reports provide data and information on karst in each area. Karst data are compiled from the British Geological Survey databases on karst, springs, and transmissivity; reports and peer reviewed papers; from geological mapping; and through knowledge exchange with the Environment Agency, universities, water companies, consultants and cavers. This report shows that there is considerable evidence that the Inferior and Great Oolite group aquifers of southern England are karstic, but with substantial differences to the classical karst of the Carboniferous limestones where karst is much more obvious. Dissolution pipes appear to be absent or rare, perhaps due to the limited unconsolidated cover in the J3 area. There are records of dolines, but the dataset is incomplete and there has been little work on dolines in this area. There is little evidence of cave development, although some short caves have been observed in the Inferior Oolite Group. Smaller conduits (~10 to 30 cm) have been observed in underground stone quarries and at spring outlets. Information on karstic conduits from boreholes and outcrops have not been collated for this report, and it is unclear how commonly they occur. Hydrogeological studies of the area suggest that solutional fissures are very common. Small stream sinks are also common in some areas, and may be present in others as there has been no systematic survey. Rivers have highly karstic characteristics, with some big losses as they pass over the Great and Inferior Oolite group aquifers, sometimes via distinctive “swallow holes”. Many are fed by large springs and commonly exhibit karstic bourne behaviour. More than 5000 springs have been recorded in the Great and Inferior Oolite group limestones. Discharge data are sparse. Many appear to be small with maximum flows of ~ 1 l/s but there are also 32 with large recorded flows of > 10 or > 100 l/s, and it is likely that there are many more large springs, and also that flows in the natural spring outlets have been greatly reduced by the exploitation of groundwater for supply. Tracer tests by Smart (1977a,b) in the By Brook catchment have demonstrated very rapid groundwater flow over distances of several kilometres, with velocities based on first arrival of tracer of up to 10 km/day, and velocities based on peak tracer concentrations ranging from 0.2 to 5.2 km/day (mean of 2.03 km/day). Tracer recoveries were high (5 to 95%), but breakthrough curves had extensive tailing suggesting attenuation and dilution along the flow paths. Other evidence of karst includes: some high transmissivities, some high borehole yields, rapid aquifer responses to rainfall, and responses to pumping over long distances. The Great and Inferior Oolite group aquifers appear to comprise extensive networks of solutional fissures and conduits, with many flow paths enlarged to a small degree, rather than a small number enlarged to form cave networks. Further investigation of karst (e.g. dolines, stream sinks, spring discharges, tracer tests, water quality indicators of rapid flow) would enable improved conceptualisation of the Inferior and Great Oolite group aquifers, and would be useful to assist with the protection and sustainable management of groundwater resources.

Item Type: Publication - Report
Funders/Sponsors: British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed, but not externally peer-reviewed.
Additional Keywords: Groundwater, GroundwaterBGS
Date made live: 04 Sep 2023 12:14 +0 (UTC)

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