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Letter to the Editor |
Institute of Geological Sciences (Hydrogeological Department), , Exhibition Road, LONDON SW7 2DE.
I read the work on the Chalk groundwater of the Horndean-Havant area with interest. I entirely agree with the authors' claim that their tracer investigations provide unequivocal evidence of the existence of highly-localised, very rapid, probably turbulent, conduit flow of Chalk groundwater, at least at that location.
Part of their discussion and conclusions however, namely the suggestion that similar near-karstic features are generally responsible for the widespread existence of zones of high transmissivity, is distorted and likely to lead to the results being quoted out-of-context by non-groundwater specialists. Comparable conditions are only likely to be found at occasional locations mainly along the margin of the Tertiary outcrop where Chalk solution has been accelerated by concentrated run-off or recharge of low pH; certain examples are known from the London Basin (Water Resources Board 1972). Subaerial weathering on the Tertiary erosion surface will also have contributed to the development of secondary permeability. Indeed, is it not possible that the main conduits of the flow system described in the paper are developed along the Cretaceous-Tertiary unconformity?
Now high fissure transmissivity is one thing but near-karstic conduits (in which transmissivity is a meaningless concept and for which the basic laws of porous media hydraulics do not even approximately apply) are another. It is fair to say that high fissure transmissivities (over 500 m2/d and often over 1000 m2/d) are developed over wide areas of the Chalk outcrop intake area. It is such areas that are of greatest volumetric importance and most topical interest in
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This article has been cited by other articles:
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  M. Price Fluid flow in the Chalk of England Geological Society, London, Special Publications, 1987; 34: 141 - 156. [Abstract] [PDF]
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