A method for computing and comparing upward flow of water in soils from a water table using the flux/unsaturated conductivity ratio

Abstract

A new method, based on an analysis of the k-h curves in relation to their use in the flow equation, is proposed for the study of steady-state upward flow of water in soils from a water table and for the computation of the pressure head profiles. This method utilizes the flux/unsaturated conductivity ratio to provide a simplified but accurate means of computing pressure head profiles, using an algebraic equation for any given rate of upward flow, between specific values of pressure heads. The values of the parameters to be used in solving this equation can be read directly from the k-h curves. In many soils, upward flow can be characterized by two parameters, namely, the slope of the k-h curve and the upper limit h,, of the critical pressure head range, thus giving a basis for direct comparison. This method can be applied to k-h curves with any integer or non-integer value of slope. Equations are also derived from which the maximum depth to water table for any rate of upward flow can be read directly from the k-h curves of certain soils. The flux/unsaturated conductivity ratio is also used to define the critical range of unsaturated conductivity, and the corresponding critical pressure head range within which the absolute values of conductivity significantly affect the shape of the pressure head profile. The use of the flux/unsaturated conductivity method, and the critical ranges for analysing k-h curves in order to predict and compare upward flow in homogeneous and layered soils, are discussed.