Planning and Interpreting Soil Permeability Measurements

Field techniques for measuring soil hydraulic conductivity (below the water table as well as above, or in the absence of, a water table) are considered, in selecting a technique for a given situation, care should be taken that the soil region and dominant flow direction in the system to be analyzed or predicted are as closely duplicated by the technique as possible. If the soil region covered by an individual measurement is small compared to that of the actual system, measurements at different depths and locations are necessary. The resulting values will seldom if ever be uniform and simplification to manageable media may be required. The average hydraulic conductivity of a randomly heterogeneous medium must lie between the harmonic and the arithmetic mean. Studies with a resistance network analog show that this average hydraulic conductivity is best estimated by the geometric mean.