Determination And Prediction Of Soil Water Characteristic Curve In Unsaturated Zone

Unsaturated zone is also called the vadose zone, which is the connection of surface water, soil water and groundwater, in which the flow of gas and liquid as well as the transfer and transform processes of various material components have been happened. Due to the water exchange between atmosphere and deep aquifer cannot lack of the transition zone, as a result, the moisture movement within the unsaturated zone plays an vital role in the whole water cycle activities. Soil water characteristic curve(SWCC) is a curve describes the relationship between soil suction and water content in unsaturated zone, which can reflect the relationship between soil water quantity and energy, and plays a significant role in researching water flow and solute transport in the unsaturated zone. Soil water characteristic curve is a highly nonlinear function, the relationship between them is complicated and difficult to deduce the exact relationship theory, therefore, measuring and projections for soil water characteristic curve is of great significance.In support of the project called ‘Hydrogeological parameters survey about large basin in Northwest, this paper has in-depth researched the determination and prediction of soil water characteristic curve. The main content of the research are obtained as follows:1. Using the Ku-pF apparatus to measure the six kinds of sample’s soil water characteristic curve, and comparatively analysing the variation of soil water characteristic curve under different particle sizes. The results indicated that particle size influence on soil water characteristic curve is through to reflect the influence on the soil porosity. The pore structure became dense with the decrease of the soil particle size, the medium and small pores of soil increased and the pore connectivity became poor, indicating that the soil has a high air entry value and relatively large water resistance.2. Using five different empirical models to fit the measured soil water characteristic curve and discuss the differences of fitting results with different particle sizes. Combining with the physical background of fitting parameters to evaluate the different models. The results showed that the coefficient of determination of Van Genuchten model were reached above 0.95 and the fitting parameter values were also in accordance with its actual physical background, which was the optimal model to describe the soil water characteristic curve.3. On the basis of the basic physical properties of soil, using two physico-empirical method, which named Arya-Paris(AP) model and Non-similar midia concept(NSMC) model, to indirectly predict the soil water characteristic curve, and comprehensively evaluate the prediction precision of the two methods. The results showed that the AP model was superior to NSMC model on prediction precision,and more suited to predict silty sand and silt, those soils with medium texture. While using Arya-Paris method, the scaling parameter, α, should be discussed. It was found that the AP model with non-linear α was the best method to estimate SWCC, but AP model with constant α was the worst.