Volume of Water

on . Posted in Geotechnical Engineering

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Volume of water, abbreviated as \(V_w\), is the amount of water that a given volume of soil can hold or retain.  This property is often expressed as soil moisture content and is an essential factor in agriculture, horticulture, and environmental science.  Soil moisture content is typically measured as a percentage, representing the ratio of the volume of water present in the soil to the total volume of the soil.  Soil moisture content can vary depending on several factors, including soil type, texture, porosity, and environmental conditions.  Soils with larger particles and greater pore spaces, like sandy soils, may have a lower moisture retention capacity compared to finer textured soils, such as clay soils.

Soil moisture content methods and instruments used

  • Gravimetric Method  -  This involves weighing a soil sample before and after drying it in an oven to determine the moisture content by the difference in weight.
  • Tensiometers  -  These instruments measure the soil's water potential, which can indirectly indicate the soil moisture content.
  • Time Domain Reflectometry (TDR) and Frequency Domain Reflectometry (FDR)  -  These electronic methods use sensors to measure the dielectric constant of the soil, which is related to its moisture content.
  • Neutron Probe  -  This method involves the use of a neutron source and detector to measure soil moisture content based on the number of neutrons scattered by water in the soil.
  • Soil Moisture Sensors  -  Various types of sensors, such as capacitance sensors and resistance sensors, can directly measure the moisture content of the soil.

Understanding the soil volume of water is crucial for agriculture to determine when and how much to irrigate crops, as well as for environmental studies to assess water availability and the potential for groundwater recharge.  It can also impact construction and engineering projects, as soil moisture content can affect soil stability and compaction.


Volume of water formula

\( V_w =  k \; i \; A_c \; t   \)     (Volume of Water)

\( k =   V_w \;/\; i \; A_c \; t \)

\( i =  V_w \;/\; k \; A_c \; t \)

\( A_c =  V_w \;/\; k \; i \; t \)

\( t =  V_w \;/\; k \; i \; A_c  \)

Symbol English Metric
\( V_w \) = volume of water \(ft^3\) \(m^3\)
\( k \) = permeability coefficient \(ft \;/\; sec\) \(m \;/\; s\)
\( i \) = hydraulic gradient \(dimensionless\)
\( A_c \) = area cross-section \(ft^2\) \(m^2\)
\( t  \) = duration of time for collection of water \(sec\) \(s\)


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Tags: Volume Water Soil