Groundwater — storage coefficient of a compressible confined aquifer For a confined aquifer with finite compressibility, on what parameters does the storage coefficient (S) primarily depend?

Introduction / Context:
The storage coefficient S of a confined aquifer quantifies the volume of water released from storage per unit plan area per unit decline in hydraulic head. In confined systems, water is released primarily due to elastic compression of the aquifer skeleton and expansion of the pore water, not by gravity drainage (which dominates in unconfined aquifers via specific yield).

Given Data / Assumptions:

• Confined aquifer with thickness b.
• Compressibility of aquifer matrix (α) and water (β) are finite.
• Water unit weight γ_w relates head change to pressure change.

Concept / Approach:
The specific storage Ss (per unit thickness) is given conceptually by Ss = γ_w * (α + n * β), where n is porosity. The storage coefficient is S = Ss * b, indicating dependence on γ_w, aquifer thickness b, aquifer compressibility α, and water compressibility β (weighted by porosity). Permeability and transmissibility govern flow rates, not elastic storage in a confined setting.

Step-by-Step Solution:
Identify elastic contributors: matrix compression (α) and water expansion (β).Relate pressure change to head via γ_w; include thickness b for total storage per area.Conclude S depends on γ_w, b, α, and β (with porosity influence via n in Ss).

Verification / Alternative check:
Textbook derivations consistently show S = γ_w * b * (α + nβ), confirming the listed dependencies and excluding permeability/transmissibility.

Why Other Options Are Wrong:
Options involving permeability or transmissibility confuse hydraulic conductivity (flow capacity) with storage; specific yield pertains to unconfined aquifers.

Common Pitfalls:

• Assuming specific yield controls confined aquifer storage.
• Mixing up transmissibility (T = K*b) with storage parameters.

Final Answer:
Specific weight of water, aquifer thickness, compressibility of the aquifer skeleton, and compressibility of water