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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