NEW MODELS FOR UNSATURATED SOIL HYDRAULIC-PROPERTIES

Two relatively simple models are proposed for describing the soil wate r retention curve. The expressions define sigmoidal or bimodal type re tention functions with four or five parameters, respectively. The sigm oidal retention model may be combined with predictive pore-size distri bution theories to yield closed-form equations for the unsaturated hyd raulic conductivity. Parameters in the proposed hydraulic functions we re estimated from observed retention data using a nonlinear least-squa res optimization process. The models were tested on hydraulic data for more than 20 soils. Good agreement between predicted values and measu red retention and conductivity data was found for most of the soils. T he soil hydraulic models can be effectively utilized as inputs for num erical models of water flow and solute transport.