This report documents the evidence for karst and rapid groundwater flow in the Chalk of East Anglia. 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.
This report shows that there is a surprising amount of evidence for karst in East Anglia, despite the extensive and often thick superficial deposits that cover much of the Chalk following the Anglian glaciation. Paleokarstic features provide evidence of karstification prior to the Anglian glaciation, and post Anglian karst development is also occurring. Although there are only a few studies of karst specifically, considering the different strands of evidence, it is clear that karst processes impact the Chalk throughout the area.
A small karst cave is present in the Chalk at one location on the north coast, and other small caves may be present beneath the superficial cover. Karst networks in the area are likely to comprise fissures and conduits, and the extent to which some of these are enlarged to form small caves is difficult to assess given the limited outcrops and exposures. Dissolution pipes are common, many are large, and some provide evidence of paleokarst that pre-dates the Anglian glaciation. Extremely high densities of surface depressions occur, and it is often difficult to determine if they are of periglacial, anthropogenic, or karstic origin. However, it is clear that many are anthropogenic and that some are likely to be karst dolines. Stream sinks occur, with some classic chalk karst stream sinks in the south of the area associated with the Chalk-Paleogene boundary. Many stream sinks are associated with the Chalk-glacial till boundary, and although these are small scale features, collectively they may be important for recharge in some areas. Some streams on the Chalk (and where there is thin permeable cover) have losing sections and/or exhibit bourne behaviour.
Karstic recharge is unlikely over large parts of East Anglia where there are thick deposits of glacial till overlying the Chalk. Nevertheless, there are areas where some karstic flow in the unsaturated zone is likely. This is most likely where there are stream sinks or river losses to the Chalk, and may also occur in a more limited way in association with dissolution pipes/dolines where there is thin cover, and also in areas of outcrop Chalk if there are vertical solutional fissures with no surface expression. Further assessment of surface karst features and consideration of water quality indicators of rapid flow at springs and abstractions would provide insights into unsaturated zone karst in East Anglia.
There is more widespread evidence for saturated zone karst. A small number of tracer tests from monitoring boreholes to abstraction boreholes or springs have demonstrated rapid groundwater flows of 14 to >3800 m/day over distances of 44 to 1650 m. Extensive networks of solutional fissures and conduits are also indicated by the many groundwater abstraction sites with high transmissivity (> 1000 m2/day) which are distributed throughout East Anglia. There are also many springs, some of which are reported to be (or have been) large, including some with measured discharges of > 200 l/s.
Saturated zone karst networks may occur due to mixing corrosion or due to the development of current/past stream sink to spring connections. Whilst the exact locations and extent of the saturated zone solutional networks are difficult to determine, karstic solutional development in this area appears to occur more in river valleys than interfluves; and there is often a strong geological control, with flows focused on inception horizons (that in this area include the Totternhoe Stone, the Plenus Marls, the Chalk Rock and the Top Rock).
Although there is evidence for karst throughout East Anglia, there is more evidence for karst in the south and west of the area, and in river valleys and where superficial cover is thin. Some areas with particular evidence for karst include: the Beane and Upper Cam catchments, the Gipping valley, the Cambridge-Newmarket area, the Thetford area, and the Burn and Bure catchments in the north.
Karst is clearly an important aspect of the hydrogeology of East Anglia. Further work would be useful to improve datasets on dissolution pipes, dolines, stream sinks and springs which are generally very incomplete in this area; and further studies of these features would also be useful to determine their characteristics and their hydrogeological role. Further tracer testing and further consideration of pumping test data in the context of karst would also be useful
