Macroporous drainage of unsaturated swelling soil

A general procedure for modeling one-dimensional unsteady water flow throug h unsaturated swelling soil has been developed. The generalized equation is based on Richards' [1931] equation for unsaturated flow. The developed equ ation and its numerical solution used in the procedure can be applied to th e study of soil drainage and redistribution where the flux of water is down ward toward the water table. In this case the water content at each point i n the profile decreases with time. The derivation of the relationship betwe en volume changes and corresponding water losses reflects the effect of dif ferent shrinkage phases for a clayey soil. The model partitions the soil in to two domains: macropores and micropores. To verify the model, results are compared with two other models. The model is then applied, using Regina cl ay as a media, to demonstrate the effect of volume change on moisture profi les during drainage. The results demonstrate that errors will occur if the classical theory of water movement in a nonswelling soil is employed to des cribe water flow in an unsaturated soil that exhibits volume change during wetting and drying.