Introduction

• Knowledge of water flow under saturated conditions is important to engineers, soil scientists, and agronomists.
• The data on volume and rate of flow of water in soil are needed for managing soils and plant growth.
• The water movement through a soil system influences aeration, nutrient availability to the plants, and soil temperature. Important applications of saturated flow in farmlands involve design of a surface and subsurface or tile, drainage system in a watershed. Most drainage designs are based on steady flow under saturated conditions.
• In saturated soils, the entire soil pores (micro and macro pores) are filled with water. In this case, the volumetric water content is equal to the total porosity and air-filled porosity is equal to the zero.
• The movement of water through a porous system occurs whenever there is a difference in potential energy of water within the porous matrix. The water content and water flow in a saturated soil system do not change with time during flow which is called steady state flow and only positive potentials are the driving force during the water transport.
• Saturated flow is determined by hydraulic force or hydraulic gradient and hydraulic conductivity of soil i.e. ease with which soil pores permit water movement.
• Water movement is always described in terms of potentials. The total potential of soil water is the sum of the gravitational, pressure, and osmotic potentials.
• The difference in potential energy of water builds a force in the system, which forces the water to move from a position of greater potential (energy) to smaller potential (energy).
• In most of the water movement, osmotic potential is neglected and hydraulic potential considered which involves pressure potential (Hp) and gravitational potential (Hz).