Combined Brooks-Corey/Burdine and van Genuchten/Mualem Closed-Form Model for Improving Prediction of Unsaturated Conductivity

The performance of the widely used conventional closed-form models of Brooks and Corey and van Genuchten is restricted to soils characterized by a specific shape form of the water retention curve. Hence, the van Genuchten model more accurately describes “S”-shaped retention curves characterizing finer-textured soils, whereas the Brooks-Corey model is much better adapted for “J”-shaped retention curves characterizing relatively coarse-textured soils. In this work, a new closed-form soil hydraulic model is proposed. The suggested continuous-form function accurately describes soil retention curves irrespective of their specific shape form. New algebraic expressions based on Mualem’s statistical model and another new model that is a combination of the Mualem and Burdine theories were derived for the prediction of the unsaturated hydraulic conductivity function. Comparisons of ten soils known from international bibliography were performed. It is concluded that the proposed water retention curve expression as well as the hydraulic conductivity predictions showed significant improvement over the conventional van Genuchten and Brooks-Corey closed-form models, particularly for conductivity values near the residual water content and saturation.