The capacity of a material to allow fluids to pass through it, expressed as the volume flow rate of water through a cross-sectional area of a porous medium (see porosity; permeability) under the influence of a hydraulic gradient of unity at a specified temperature. This depends on properties of the fluid and the medium. It is measured in units of metres per second or metres per day and varies with temperature. Typical values range from 10−6 m/day for clay to 103 m/day for coarse gravel.
http://www.connectedwater.gov.au/framework/hydrometric_k.php. Measuring hydraulic conductivity explained.
Subjects: Ecology and Conservation.