Drip Irrigation System:
Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, fruit, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 (completely dry) to the value of the materials' porosity at saturation.
It can be given on a volumetric or mass (gravimetric) basis. Volumetric water content, θ, is defined mathematically as: where is the volume of water and is the total volume (that is soil volume + water volume + air space). Gravimetric water content [1] is expressed by mass (weight) as follows: where is the mass of water and is the bulk mass. The bulk mass is taken as the total mass, except for geotechnical and soil science applications where oven-dried soil (,see the diagram) is conventionally used as .
To convert gravimetric water content to volumetric water, multiply the gravimetric water content by the bulk specific gravity of the material. In soil mechanics and petroleum engineering , the term water saturation or degree of saturation, is used, defined as where is the porosity and is the volume of void or pore space. Values of Sw can range from 0 (dry) to 1 (saturated). In reality, Sw never reaches 0 or 1 - these areidealizations for engineering use.
The normalized water content, , (also called effective saturation or ) is a dimensionless value defined by van Genuchten [2] as: where is the volumetric water content; is the residual water content, defined as the water content for which the gradient becomes zero; and, is the saturated watercontent, which is equivalent to porosity, .