On some apparent paradoxes in water spreading,hydrology and seepage

In water spreading and underground hydrology, one should beware of pitfalls. This is illustrated by several examples of vertical downflow and upflow. Drainage by overcharging: When a fine-grained soil overlies a coarse-grained soil, a certain amount of water can be suspended in the interzone. Adding water may cause excessive drainage. Cavitation in soils: When water flows from an upper less pervious layer to a more pervious layer, the pressure head in the interzone may become negative, the gases dissolved are released in the form of bubbles which render the soil temporarily impervious. At the initial instant of seepage of water from a pond into a dry soil, inertial forces and kinetic energy cannot be neglected. At the interface of two anisotropic media, the angle of refraction of a streamline depends on the tangential hydraulic conductivity only, whereas that of a gradient line depends on the normal component only. Impossibility of steady-state evaporation from a deep water table: It is shown that the water concentration may become negative, which is physically impossible. Two modes of downflow: In insaturated downflow there exists a critical water concentration c such that the corresponding hydraulic conductivity K(c) is equal to the descending specific flux. The moisture distribution is radically different in the subcritical and supercritical zones.