ABSTRACT
The two properties of a rock or soil which are most important in controlling the behaviour of subsurface water are how much water the rock or soil can hold in empty spaces within it, and how easily and rapidly the water can flow through and out of it. Flow of water through a soil or rock is described empirically by Darcy's Law, and the relative ease of flow by the hydraulic conductivity. The chapter discusses the relationships between hydraulic conductivity, permeability and water-yielding capacity. Rocks must have voids, in order to have permeability and hydraulic conductivity, but the relationship between porosity and permeability depends mainly on the size of the voids rather than on their frequency. The chapter describes the relevance of the laboratory experiment to natural phenomena, particularly the flow of groundwater and the pressure of pore water. Groundwater normally contains impurities such as carbonates and sulphates, which were dissolved from the rocks with which it came in contact.
