Correlations between rock and water characteristics of the Inferior Oolite aquifer, central Cotswolds, UK

Abstract

This study documents the results of an intensive sampling campaign of Jurassic Lower Inferior Oolite limestone and spring water along the lower River Frome valley, near Stroud, in the Cotswold Hills, UK. Our dataset includes discharge measurements from 25 small springs (ranging from 0.04 to 0.71Ls−1), and evaluations of water pH and hardness (dissolved CaCO3) at 15 of these springs. Where possible, samples of in situ limestone were extracted from the spring outcrops, resulting in 30 measurements of local porosity, permeability, and hydraulic conductivity, which were conducted in the laboratory. There exist striking positive correlations between spring discharge and local limestone porosity, and between discharge and water hardness. X-ray diffraction and thin section analyses revealed the important role of rock mineralogy and texture, which may influence the porosity and permeability of the limestones. Samples taken from the eastern side of the valley showed greater degrees of secondary diagenesis, the products of which reduce effective porosity, providing a possible explanation for the depressed values of spring discharge there. In the study area, springs with higher discharges correlated strongly with higher spring water hardness and bedrock porosity. This suggests that water from the limestone matrix may contribute to the springs.