A simple analytic model is proposed which predicts the unsaturated hydraulic conductivity curves by using the moisture content-capillary head curve and the measured value of the hydraulic conductivity at saturation. It is similar to the Childs and Coilis-George (1950) model but uses a modified assumption concerning the hydraulic conductivity of the pore sequence in order to take into'account the effect of the larger pore' section. A computational method is derived for the determination of the residual water content and for the extrapolation of the water content-capillary head curve as measured in a limited range. The proposed model is compared with the existing practical models of Averjanov (1950), Wyllie and Gardner (1958), and Millington and Quirk (1961) on the basis of the measured data of 45 soils. It seems that the new model is in better agreement with observations.

A conceptual model of the capillary hysteresis phenomenon is suggested. The advantage of this model is that all scanning curves are derived with the aid of simple functions from the main drying curve and the main wetting curves solely. Like the generalized approach of Enderby (1955) the present model takes into account a reversible part of the process. A simple method of predicting the first drying curve and the scanning curves branched out of the first drying curve is also proposed. Results based on this model are compared with laboratory measurements and the general Néel‐Everett independent domain model. The comparison shows that the present model is often in more satisfactory agreement with measurements for cases in which the prediction based on the Néel‐Everett model is poor. The suggested method can be used for solving problems in which hysteresis plays a significant role, the difficulties associated with laboratory determination of the ψ‐θ relationships in the whole domain thus being avoided.

A conceptual model is proposed for the prediction of the electrical conductivity of bulk soil in saturated and in unsaturated states. The model is based on the hypothesis that the tortuosity factor affecting the bulk soil electrical conductivity is identical to that defined for prediction of the soil hydraulic conductivity. Simple mathematical functions are derived to forecast the soil electrical conductivity as a function of the water content. Experimental results of seven previous studies carried out on 26 soils were used for validation tests. The model's efficiency as a predictive tool, in cases where limited experimental data are available, is found to be generally good.

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We present herein a Simplified approach to the capillary hysteresis phenomenon. This approach is based on a similarity hypothesis resembling that of Philip (1964), but different basic assumptions lead to a quite simple and handy method of predicting the relationships between the capillary held and the water content within the hysteretic loop. Only the boundary curves of the main loop are required in order to derive analytically the scanning curves. The reliability of the proposed modified model is demonstrated by a comparison of the predicted scanning curves with the measured ones. The computed results are often in more satisfactory agreement with experiments than those obtained with the use of the general N•el-Everett model.