In science and engineering, hydraulic conductivity (, in SI units of meters per second), is a property of porous materials, soils and rocks, that describes the ease with which a fluid (usually water) can move through the pore space, or fractures network. It depends on the intrinsic permeability (, unit: m) of the material, the degree of saturation, and on the density and viscosity of the fluid. Saturated hydraulic conductivity, , describes water movement through saturated media. By definition, hydraulic conductivity is the ratio of volume flux to hydraulic gradient yielding a quantitative measure of a saturated soil's ability to transmit water when subjected to a hydraulic gradient. Methods of determination There are two broad categories of determining hydraulic conductivity: Empirical approach by which the hydraulic conductivity is correlated to soil properties like pore size and particle size (grain size) distributions, and soil texture Experimental approach by which the hydraulic conductivity is determined from hydraulic experiments using Darcy's law The experimental approach is broadly classified into: Laboratory tests using soil samples subjected to hydraulic experiments Field tests (on site, in situ) that are differentiated into: small scale field tests, using observations of the water level in cavities in the soil large scale field tests, like pump tests in wells or by observing the functioning of existing horizontal drainage systems. The small scale field tests are further subdivided into: infiltration tests in cavities above the water table slug tests in cavities below the water table The methods of determination of hydraulic conductivity and other related issues are investigated by several researchers and include more empirical approaches. Estimation by empirical approach Estimation from grain size Allen Hazen derived an empirical formula for approximating hydraulic conductivity from grain size analyses: where Hazen's empirical coefficient, which takes a value between 0.0 and 1.5 (depending on literatures), with an average value of 1.0. A.F. Salarashayeri & M. Siosemarde give C as usually taken between 1.0 and 1.5, with D in mm and K in cm/s. is the diameter of the 10 percentile grain size of the material Pedotransfer function A pedotransfer function (PTF) is a specialized empirical estimation method, used primarily in the soil sciences, however has increasing use in hydrogeology. There are many different PTF methods, however, they all attempt to determine soil properties, such as hydraulic conductivity, given several measured soil properties, such as soil particle size, and bulk density. Determination by experimental