Definitions
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 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 are idealizations for engineering use.
The normalized water content, (also called effective saturation or ) is a dimensionless value defined by van Genuchten 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 water content, which is equivalent to porosity, .
Read more about this topic: Water Content
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