An Analysis of the Vertical Infiltration of Water into Soil Columns

Abstract

An experimental investigation is reported for vertical infiltration of water into a sandy loam and silt loam soil material. Water was allowed to enter air‐dry columns of soil at a small constant suction, and its subsequent distribution was followed with a gamma radiation attenuation device. An analytic expression of water content as a function of depth and time was obtained by multiple regression analysis, from which it was possible to determine the instantaneous flux and the water concentration gradient at given water contents.The relation between the flux and gradient was linear only during the early stages of infiltration. Nonlinearity at low water gradient was evidenced for both soils throughout a wide range of water contents. The magnitude and direction of the departure from linearity were similar for both soils.A new empirical flow equation, capable of fitting the data closely, was obtained by modifying the diffusivity equation for unsaturated flow. The modification consisted of raising the water‐content gradient to a power greater than unity. Under this modification, the parameter analogous to soil‐water diffusivity becomes a function of both water content and water‐content gradient.