approach There are relatively simple and inexpensive laboratory tests that may be run to determine the hydraulic conductivity of a soil: constant-head method and falling-head method. Laboratory methods Constant-head method The constant-head method is typically used on granular soil. This procedure allows water to move through the soil under a steady state head condition while the volume of water flowing through the soil specimen is measured over a period of time. By knowing the volume of water measured in a time , over a specimen of length and cross-sectional area , as well as the head , the hydraulic conductivity () can be derived by simply rearranging Darcy's law: Proof: Darcy's law states that the volumetric flow depends on the pressure differential between the two sides of the sample, the permeability and the viscosity as: In a constant head experiment, the head (difference between two heights) defines an excess water mass, , where is the density of water. This mass weighs down on the side it is on, creating a pressure differential of , where is the gravitational acceleration. Plugging this directly into the above gives If the hydraulic conductivity is defined to be related to the hydraulic permeability as this gives the result. Falling-head method In the falling-head method, the soil sample is first saturated under a specific head condition. The water is then allowed to flow through the soil without adding any water, so the pressure head declines as water passes through the specimen. The advantage to the falling-head method is that it can be used for both fine-grained and coarse-grained soils. . If the head drops from to in a time , then the hydraulic conductivity is equal to Proof: As above, Darcy's law reads The decrease in volume is related to the falling head by . Plugging this relationship into the above, and taking the limit as , the differential equation has the solution Plugging in and rearranging gives the result. In-situ (field) methods In compare to laboratory method, field methods gives the most reliable information about the permeability of soil with minimum disturbances. In laboratory methods, the degree of disturbances affect the reliability of value of permeability of the soil. Pumping Test Pumping test is the most reliable method to calculate the coefficient of permeability of a soil. This test is further classified into Pumping in test and pumping out test. Augerhole method There are