Dynamic simulatin of unsteady flow of water in unsaturated soils and its application to subirrigation system design

Abstract

Unsteady vertical flow of water in unsaturated soils was simulated utilizing S/360 CSMP (Continuous System Modeling Program), a recently developed language specially designed for digital simulation of transient phenomena that can be represented by differential equations. The principles of conservation of mass and of Darcy's law, which lead to the derivation of the unsaturated flow equation, were directly applied to specify the flow system. The boundary conditions described a no-flow situation across the top surface and an impermeable layer across the bottom of the soil mass considered. The initial condition specified a uniform pressure potential, corresponding to a water content uniform with depth. Two computer programs were developed. One simulated vertical unsteady infiltration through the surface into a homogeneous unsaturated soil. Simulation results were obtained for three different soils -- Yolo light clay, Adelanto loam, and Pachappa loam. The results for Yolo light clay compared favorably with the available numerical solutions of Philip for the same soil and for identical boundary and initial conditions. The solutions for the other two soils demonstrated the workability of the model for soils having different hydraulic characteristics. ...