Subtopic: Storativity and specific yield of aquifers
Question Statement:
Which of the following statements regarding aquifer storage properties is/are TRUE?
Options:
(A) For an unconfined aquifer, storativity ($S$) is practically equal to the specific yield ($S_y$), typically ranging from $0.10$ to $0.30$
(B) For a confined aquifer, storativity is governed by elastic expansion of water and compaction of aquifer skeleton, typically ranging from $10^{-5}$ to $10^{-3}$
(C) Porosity of an unconfined aquifer equals the sum of specific yield and specific retention ($n = S_y + S_r$)
(D) Confined aquifers release water primarily by gravity dewatering of pore spaces
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. In water table aquifers, water release is by actual gravity pore drainage, so $S \approx S_y \approx 0.1-0.3$ (A is true).
2. In confined aquifers, pores remain $100\%$ saturated; water yield is driven by compressibility, giving low $S = 10^{-5} - 10^{-3}$ (B is true).
3. Total volume of voids partitions into drained water ($S_y$) plus capillary held water ($S_r$): $n = S_y + S_r$ (C is true).
4. Confined aquifers release water via pressure decompression and matrix compressibility, never gravity dewatering (D is false).