Comparative Survey of Four Unsaturated Soil Flow Equations

Abstract

Four equations for water flow in unsaturated porous media are compared with the results of several years of data collected in the field. The equations consist of one attributed to Darcy and three developed by Klute, Morel-Seytoux, and Gelhar. The equations require different input parameters, but limiting the input variables to data collectable in a typical soil survey has been attempted. The field data (not collected by the writers) consist of monitoring the downward movement of tritiated water in a research watershed to a depth of 310 in. (787 cm). Soil moisture characteristic curves for the various soil types within the monitored depth are developed by a computer program developed by the writers. Results show that the four equations predict the rate of downward water flow with varying accuracies depending on the soil type within the profile and moisture conditions of the soil. The results are summarized in graphical and tabular form, and conclusions are drawn from the results.