For an unconfined water-table aquifer of total porosity $n$, specific yield $S_y$, and specific retention $S_r$, which exact relationship holds universally?
Options:
(A) $n = S_y + S_r$
(B) $n = S_y - S_r$
(C) $n = S_y \times S_r$
(D) $S_y = n + S_r$
Answer Key:
A
Step-by-Step Solution & Explanation
Total porosity $n$ represents the total volume fraction of voids. When an unconfined aquifer is drained by gravity, the fraction drained is the specific yield ($S_y$) and the fraction retained against gravity by molecular and surface tension forces is specific retention ($S_r$). By conservation of pore volume, $n = S_y + S_r$. Option A is correct.