Measured and Approximate Flux‐Concentration Relations for Absorption of Water by Soil

Abstract The flux‐concentration relation of Philip (1973) is calculated using moisture profiles measured during absorption of water by a fine sand when water was supplied at both constant hydraulic potential and constant rate. The general behavior of the measured flux‐concentration relations was found to be consistent with those of the model soils calculated by Philip. Within the accuracy of the measurements, no significant time‐dependence of the relation was found for the constant flux boundary condition over a large time span. Measurements of the time‐averaged flux‐concentration relation, however, suggest some significant time‐dependence for short times. Simple approximations for the flux‐concentration relation, based on these observations, are suggested. These approximations enable easily evaluated predictions to be made of the salient features of constant rate application of water to soil, which are sufficiently accurate for most practical purposes.