MODELS TO PREDICT UNSATURATED HYDRAULIC CONDUCTIVITY WITH THE USE OF RETC CODE

The soil hydraulic characteristics , the soil water content and unsaturated hydraulic conductivity are essential to many agriculture and environmental applications. There are many important methods to estimate the soil water content and unsaturated hydraulic conductivity (K), and used this technique to predict the equation parameters (theta r ,theta s , alpha ,m ,n). Three models (van Genuchten - Mualem m= 1-1/n , van Genuchten - Burdine m=1-2/n and Brooks & Corey n ->infinity) were fitted with soil moisture retention data using RETC Code .The RETC code was developed at US salinity laboratory and it used world -wide in many papers at now. Method this program allows to compare three models from the input of moisture retention curve data. In this study , calculated three relationship water content vs pressure head, relative unsaturated hydraulic conductivity with water content and pressure head respectively. And, used various closed - form analytical models for predicting the hydraulic conductivity. Van - Genuchten derived equation Mualem (1976) with a new model for predicting from the soil water retention curve . Equation Mualem's derivation leads to a simple integral formula for predicting the unsaturated hydraulic conductivity. The three model gave an excellent description of soil moisture data with van Genuchten, Mualem model (m=1-1/n) being superior over the other models having the highest coefficient of determination R2 =0.9843 and lowest sum of squares of residual SSQ = 0.0031.