A numerical model for the simulation of unsaturated vertical flow of moisture in soils

Abstract This paper describes a digital model for the simulation of non-steady unsaturated vertical flow of moisture in soils. By using an integrated formula for flow velocity errors due to averaging two conductivity values are avoided. This confines the applicability to situations in which the soil is not too dry. The model also simulates the drainage process. So it produces the depth of the groundwater table and the discharge data. Other output data are pool depth, runoff, flow velocity at every depth, moisture content and tension for every layer. A discussion is given on the errors caused by averaging conductivity values in models. A chapter is dealing with oscillations caused by too large time steps. The time steps must be chosen in such a way that errors will not be amplified but reduced. The last chapter gives the costs of computation. For soils with low permeability the model seems to be very cheap to run. A digital model as the one described is fit for short runs with many soils. For long runs with one soil an analogous model is more appropriate.