Redistribution of soil water after infiltration

Abstract

The one-dimensional vertical redistribution of water is studied following infiltration into deep homogeneous soil with an initially uniform moisture content. There is assumed to be no loss of water by evaporation or transpiration during the redistribution. Assuming two factors to be constants, a first-order ordinary differential equation is derived which can be integrated numerically to compute the mean moisture content in the surface zone of draining soil as a function of the redistribution time. The depth of the draining zone increases with time, and this can be calculated too. That these factors are relatively constant is indicated by analysis of data for several soils and wetting depths over a wide range of redistribution times. Using mean values of the factors for several soils, and only wetting values of the diffusivity and conductivity functions, predicted redistribution behaviour agrees well with experimental data in four of six soils. In the remaining cases calculation of the factors for the particular soils, using an approximate method which includes hysteresis data, gives better results. The model is applied to predict the redistribution behaviour of different soils under identical treatments, and of a single soil for various infiltration quantities and initial moisture contents.