Aquifer properties of the Chalk of England

Abstract

Aquifer properties data from 2100 pumping tests carried out in the Chalk aquifer have been collated as part of a joint British Geological Survey/Environment Agency project. The dataset is highly biased: most pumping tests have been undertaken in valley areas where the yield of the Chalk is highest. Transmissivity values from measured sites give the appearance of log-normality, but are not truly log-normal. The median of available data is 540 m 2 /d and the 25th and 75th percentiles 190 m 2 /d and 1500 m 2 /d respectively. Estimates of storage coefficient from unconfined tests have a median of 0.008 and from confined tests, 0.0006. The data indicate several trends and relationships in Chalk aquifer properties. Transmissivity is highest in the harder Chalk of Yorkshire and Lincolnshire (median 1800 m 2 /d). Throughout much of the Chalk aquifer a direct relation is observed between transmissivity and storage coefficient, reflecting the importance of fractures in governing both storage and transmissivity. Pumping tests undertaken in unconfined conditions give consistently higher measurements of transmissivity than in confined areas, probably as a result of increased dissolution enhancement of fractures in unconfined areas. At a catchment scale the data illustrate a relation between transmissivity and winter flowing streams.