Dynamic Simulation of Vertical Infiltration into Unsaturated Soils

Abstract

A dynamic simulation language (S/360 CSMP) was used to develop a computer model that simulated the vertical infiltration of water into unsaturated soil. The modeling concept consisted primarily of dividing the soil into a large number of layers of equal thickness. The net flux of water through each layer at any particular time was established by using the principles of conservation of mass and Darcy's law. The ensuing water content was then calculated by integrating the net flux by means of the fourth order Runge‐Kutta method with suitable error criteria. The cumulative infiltration was calculated from the instantaneous infiltration rates by using the same integration technique. Water content profiles with time were obtained for three different soils: (1) Yolo light clay, (2) Adelanto loam, and (3) Pachappa loam. The infiltration rate and cumulative amount were also calculated with time, a complete picture of the water intake characteristics of the soil thus being given. Our simulation results for Yolo light clay were compared with those obtained by Philip under identical boundary and initial conditions. The principal advantage of the numerical procedure is its complete generality and the ease with which numerical data on the hydraulic characteristics of the soil may be used without arbitrary assumptions or function‐fitting procedures. Also, soil inhomogeneity and special boundary conditions can easily be specified in refinements of the present program.