A measure of a material's ability to transmit water under a hydraulic gradient. It depends on both the properties of the porous medium and the fluid flowing through it.
Hydraulic conductivity (K) is a quantitative measure of the ease with which water can move through a porous medium such as soil, sediment, or rock under a hydraulic gradient. It is defined as the volume of water that flows through a unit cross-sectional area per unit time under a unit hydraulic gradient. Unlike intrinsic permeability, which depends only on the porous medium, hydraulic conductivity also depends on the properties of the fluid, specifically its density and viscosity. Values of K span many orders of magnitude, from less than 10^-12 m/s for unfractured ignite rocks to greater than 10^-2 m/s for clean gravels. Hydraulic conductivity can be measured in the laboratory using permeameter tests or estimated in the field through pumping tests, slug tests, and tracer tests. It may vary spatially (heterogeneity) and directionally (anisotropy) within a geological formation, significantly affecting groundwater flow patterns. Accurate determination of hydraulic conductivity is essential for groundwater flow modeling, contaminant transport prediction, and aquifer characterization.