A note on estimating finite difference interblock hydraulic conductivity values for transient unsaturated flow problems

Nine different methods of weighting interblock hydraulic conductivity values used for modeling one‐dimensional water transfer in homogeneous unsaturated soil are tested for their influence upon the accuracy of the finite difference solution. On the basis of these results the most suitable weighting relation is selected. In a first stage the numerical results obtained by the models using the various conductivity weighting formulas are compared with the quasi‐analytical solution developed by Philip for a clay soil. In a second stage the models are used to simulate a laboratory experiment carried out on a sandy soil. In both cases, rather drastic boundary conditions are applied. It appears clearly from these tests that the weighting errors are of critical influence on the accuracy of solution. As proposed in this note, the geometric mean taken over two adjacent hydraulic conductivity values is the only weighting method that generates little weighting error. The latter weighting relation is found to be preferable in terms of flexibility, precision, and feasibility.