ارزيابي مدل هاي شبيه سازي منحني مشخصه آب خاك بر اساس توزيع دانه بندي ذرات خاك

Evaluation of soil moisture charachteristic curve simulating models based on particle size distribution in nine soil texture class

Soil moisture characteristic curve (SMC) is an important hydraulic characteristics of soil in design of irrigation and drainage systems, determination of hydraulic conductivity, and contaminants transport study in porous media. Direct method in the derivation of SMC is often costly and time consuming. Hense, physical and empirical models are widely used to simulate SMC. The main objectives of the present study were to compare the actual SMC with those predicted from Arya and Paris (1981), Arya et. al. (1999), and Tyler and Wheatcratt (1989) models and to modify the simulated results with scaling parameter (a) applicable for different types of soils. The input data for these models ara particl-size distribution and a parameter. In this study, nine different soil series from Urumie and Salinas regions representing wide range of soil texture class from loamy sand to clay were examined. Results indicated that the simulated SMC without modifying a parameter for particle sire distribution are significantly different from the measured SMC, and the deviation in a for each type of soils is the major factor in the discrepancies. Hence, the scaling parameter a plays a major role in the simulation process. The parameter a is generally evaluated by a relationship in the form of alphai = (a+blog (Wi /Ri^3))/logn;. in the present study, empirical coefficients a and b were determined for nine soil texture classes. Results indicated that with a= log (314 PiPs)) and b=1.01 6 e- ^0.953 , a could be calculated regardless of soil texture. thereby. the simulation of SMC could he accurately possible. Simulated SMC were in good agreements with the experimental ones, and the relative error was in the order of 0.79% indicating a great accuracy in SMC prediction.