How do water effect soil?

Answer 1

Water in soil moves from points where it has a relatively high energy status to points where its energy status is lower. Two factors determine the energy status of water at any given point in a non-saline soil. The first factor is the elevantioal position in the soil relative to a reference level. The higher an object is located above the reference level, the higher is its gravitational energy. This is true also of any given quantity of water in soil: the higher the water is located in the soil profile, the higher is its gravitational energy (g). Gravitational energy is expressed as the number of centimeters (or inches) above or below an arbitrarily chosen reference level.

The second factor determining the energy status of water is the water's pressure head (h) , as discussed in part 2. Pressure heads are negative in unsaturated soil where not all the pores are water-filled. Those that are water- filled act in a manner similar to capillaries and exert suction on water. On the other hand, pressure head can be positive, as occurs in the saturated zone below the surface of the water in soil (the "water table"). There, all or nearly all (allowing for some trapped air) pores are filled with water. Pressure head is equal to zero (h =0) at the water table. It becomes progressively higher (more positive) with increasing distance below the water table. Pressure head becomes progressively lower (more negative) with increasing distance above the water table.

The hydraulic head (H) at a given point in the soil is equal to the sum of the gravitational and pressure heads, at that point, as illustrated schematically in Figure 1 for selected conditions.