Development of soil water characteristic equations for various soil texture classes

Abstract

The investigation of unsaturated soil through numerical modeling requires the prior information on soil properties including Soil Water Characteristic (SWC) equation. Acquiring these data for different soil texture classes is laborious and time-consuming. Consequently, there is a need for predefined dataset numerical modeling of unsaturated zone in different soil texture classes. In this study, 32 soil samples were collected from different locations, and soil physical properties like particle size distribution, particle density, bulk density, porosity, and saturated hydraulic conductivity were determined. Six different soil texture classes have been found in this study and average properties were computed for each soil texture class. SWC curves were developed for all soil samples using pressure plate apparatus. Based on average SWC curves, optimal parameters of four different SWC equations (Brooks and Corey, Campbell, Van Genuchten, and Fredlund and Xing models) were determined using non-linear regression with the Trust Region Optimization algorithm with R 2 and RMSE values ranging from 0.9650 to 0.9983 and from 0.0018 to 0.0219 cm3/cm3, respectively. All the four SWC models were compared using Taylor diagrams, which show that Fredlund and Xing models are the best models among the four. Further, the performance of developed SWC equations was compared with the moisture content of UNSODA datasets and results were satisfactory as RMSE ranges from 0.0381 to 0.1265 cm3/cm3. Thus, this study provides a reliable SWC equation for different soils in Bihar.