تعیین هدایت و پخشیدگی هیدرولیکی در خاک غیر اشباع با استفاده از دستگاه صفحات فشاری و انتخاب مناسب‌ترین مدل شبیه‌ساز

Hydraulic coefficients of a porous media such as hydraulic conductivity K(θ) and diffusivity D(θ) have a controlling role in the evaluation of groundwater flow and pollutant transport behavior. Therefore, successful porous media flow evaluation depends on the accurate determination of its hydraulic coefficients. But it is hard and time consuming to measure. Values for these coefficients accurately as measurements usually task place at a moisture range close to saturation. This situation justifies the preference for prediction models to be used. One method for evaluation of K(θ) and D(θ) coefficients is to use models which take measured soil moisture characteristic curve data into consideration. For the purposes of the present study, pressure plates apparatus measured the required data to develop soil moisture characteristic curve for nine various soil textures. The volume of instantaneous outgoing water was measured with respect to time and the total volume of water released at the end of each experiment was measured for a given pressure (0.1 to 1.5 Mpa) imposed on undisturbed soil samples. A simple equation based on Richard’s equation is provided for the estimation of K(θ) and D(θ). Application of Mualem, van Genuchten et. al, Burdine, Green and Corey, and Gardner models for estimation of the K(θ) and D(θ) values at a variety of nine varied soil textures under experiment showed a wide range of variation. Therefore, it is hard to simulate the accurate hydraulic conductivity behavior for the given varied soil textures by means of the models available. However, if the minimum and maximum simulated values obtained from the models at respective soil moisture contents are considered to be a permitted range, one may state that the results of the estimated hydraulic coefficients by the proposed method in this study lie within the permitted range or agree with the results of other models considered. Therefore, the proposed method for determination of K(θ) and D(θ) is capable of selecting the best simulation model to estimate hydraulic coefficient values.