What term is defined as the ratio of the volume of water drained due to gravity to the total volume?

• A. Porosity
• B. Hydraulic Conductivity
• C. Specific Yield
• D. Specific Retention

Answer: (C)

The concept being tested is the portion of water that can drain from a porous medium under gravity relative to the medium’s total volume. This is specific yield. It’s defined as the volume of water that drains due to gravity divided by the total volume of the sample. It differs from porosity, which is just the fraction of void space, and from specific retention, which is the water retained by capillary forces after drainage. In many soils, total porosity equals the water that can drain (specific yield) plus the water that remains due to capillary forces (specific retention), with coarser materials generally having higher specific yield than finer ones.