In the design of drainage and irrigation systems, engineers (with rare exception) have made simplifying assumptions that soil is either completely saturated with water or is completely unsaturated and that resistance to flow of air (associated with the movement of water into and out of soil ) is negligible.  Such assumptions are in most cases far from realistic.   In real cases, there exist functional relationships among the saturation, the pressure difference between air and water, and the permeabilities of air and water.    A one-dimensional flow model is developed for predicting vertical flow in the unsaturated zone of the homogenous soils.   The model is developed based on the pressure head form of Richards (1931) equation.   This form is chosen to couple the unsaturated flow model with saturated flow models. The analytical solution describes the development of the moisture content profile during constant infiltration and capable of predicting the time dependence of both soil moisture content and soil moisture potential.  

U G C-CA S   in Fluid Mechanics, Department of Mathematics, Bangalore University, Central College Campus, Bangalore – 560 001.

*Faculty of Engineering – Civil, Jnanabharathi, Bangalore University, Bangalore-560 056. Karnataka. India.  
E-mail: granganna @ yahoo.com