GATE AG 2017 • Q19 MCQ • 1 Mark

Section 4: Soil and Water Conservation Engineering

Hydrology

Subtopic: Runoff estimation

Question Statement:

The sum of ‘specific yield’ and ‘specific retention’ for an unconsolidated geologic formation is equal to its

Options:

  • (A) effective porosity
  • (B) total porosity
  • (C) micro-porosity
  • (D) macro-porosity

Official Answer Key:

B

Step-by-Step Solution & Explanation

• Total porosity of an aquifer material is partitioned into (i) specific yield — the water that drains freely under gravity, and (ii) specific retention — the water held back by molecular/surface-tension forces against gravity drainage. • By definition, Specific yield + Specific retention = Total porosity. • Final Answer: (B) total porosity

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