II-2-Application of RETC Software Program in Estimation of Soil Hydraulic Parameters in Lokapavani Catchment.

Abstract

Interest in the unsaturated (vadose) zone has dramatically increased in the recent years because of growing evidence and public concern that the quality of subsurface enviorenment is being adversely affected by industrial, municipal and agricultural activities. While a large number of laboratory and field methods have been developed over the years to measure the soil hydraulic functions, most methods are relatively costly and difficult to implement. Accurate in situ measurement of the unsaturated hydraulic conductivity has remained especially cumbersome and time consuming. Water retention curve q(h) and hydraulic conductivity function k(q) of the unsaturated soils are the key parameters in any quantitative description of water flow into and through the unsaturated zone. The RETC (RETention Curve) software uses the parametric models of van Genuchten and Brooks-Corey to represent the soil water retention curve and theoretical pore size distribution models of Mualem and Burdine to predict the unsaturated hydraulic conductivity function from observed water retention data. For this study, disturbed and undisturbed soil samples were collected at 17 locations in the Lokapavani catchment under K.R. Sagar command in Mandya district of Karnataka state. From disturbed soil samples, grain size distribution and soil moisture retention data were obtained and from undisturbed soil samples, saturated hydraulic conductivity was measured in the laboratory. Using these data as input to the RETC software, Brooks-Corey parameters (a, n) were determined to derive the retention characteristic and unsaturated hydraulic conductivity. The values of a and n parameters for Brooks-Corey model were found to vary from 0.01936 to 0.22560 and 0.24647 to 0.82137 respectively. These results (as necessary input for unsaturated zone modeling) will be helpful for prediction of soil moisture flow and groundwater recharge in Lokapavani catchment.