3.5  Volumetric Moisture Content

William W. Woessner; Eileen P. Poeter

3.5 Volumetric Moisture Content

Another term used to describe the amount of water held in a porous material is the volumetric moisture content, θ. The volumetric moisture content is equal to the ratio of the volume of water, V_W, to the total volume, V_T, and is reported as either a decimal fraction or a percent. The moisture content of a sample will differ from the effective porosity if the pores are partially filled with water and partially filled with air as occurs in the vadose zone (Equation 9).

$\displaystyle \theta=\frac{V_W}{V_T}$

(9)

where:

θ	=	moisture content (dimensionless)
V_W	=	volume of water in the pore space (L³)

When earth materials are not fully saturated then only some of the connected pores are filled with water and θ < n_e. When the material is fully saturated, all connected pores are filled with water and θ = n_e. The degree of saturation is described by the ratio of the moisture content to the interconnected porosity as shown in Equation 10.

Degree of Saturation = $\displaystyle \frac{\theta}{n_e}$

(10)

The volumetric moisture content is generally used when discussing water conditions in the vadose zone because, by definition, the vadose zone is not fully saturated and the ease with which water moves through a material varies with the degree of saturation.

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