ABSTRACT
Unsaturated flow of water is a more commonly prevailing condition in the field than saturated flow. An unsaturated soil zone, or vadose zone, provides a continuum of waterunsaturated subsurface porous media connecting the soil/atmospheric interface and underlying saturated groundwater zone. It has several functions including (i) storage of water and nutrients, and (ii) transmission of water and other substances. The storage of water and nutrients is vital to the biosphere, and the water transmission is important for replenishing the aquifers. Unsaturated flow conditions are more complex and very often do not have direct solutions. Instead indirect methods, approximations, and numerical methods are more commonly used in the solution of unsaturated flow problems. This chapter describes the various laws governing the unsaturated flow through porous soil system.
